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Sample records for qcd coulomb gauge

  1. Two-dimensional QCD in the Coulomb gauge

    International Nuclear Information System (INIS)

    Kalashnikova, Yu.S.; Nefed'ev, A.V.

    2002-01-01

    Various aspects of the 't Hooft model for two-dimensional QCD in the limit of infinite number of colours in the Coulomb gauge are discussed. The properties of mesonic excitations are studied, with special emphasis on the pion. Attention is paid to the dual role of the pion. which, while a genuine qq-bar state, is a Goldstone boson of two-dimensional QCD as well. In particular, the validity of the soft-pion theorems is demonstrated. It is shown that the Coulomb gauge is the most suitable choice for the study of hadronic observables involving pions [ru

  2. Infrared behavior of the Faddeev-Popov operator in Coulomb gauge QCD

    International Nuclear Information System (INIS)

    Nakagawa, Y.; Saito, T.; Toki, H.; Nakamura, A.

    2007-01-01

    We calculate the eigenvalue distribution of the Faddeev-Popov operator in Coulomb gauge QCD using quenched SU(3) lattice simulation. In the confinement phase, the density of the low-lying eigenvalues increases with lattice volume, and the confinement criterion is satisfied. Moreover, even in the deconfinement phase, the behavior of the FP eigenvalue density is qualitatively the same as in the confinement phase. This is consistent with the fact that the color-Coulomb potential is not screened in the deconfined phase

  3. Perturbative ambiguities in Coulomb gauge QCD

    International Nuclear Information System (INIS)

    Doust, P.

    1987-01-01

    The naive Coulomb gauge Feynman rules in non-abelian gauge theory give rise to ambiguous integrals, in addition to the usual ultraviolet divergences. Generalizing the work of Cheng and Tsai, these ambiguities are resolved to all orders in perturbation theory, by defining a gauge that interpolates smoothly between the Feynman gauge and the Coulomb gauge. The extra terms V 1 +V 2 of Christ and Lee are identified with certain two-loop ambiguous terms. However, there still seem to be unsolved problems connected with renormalisation. copyright 1987 Academic Press, Inc

  4. Hamiltonian approach to QCD in Coulomb gauge at zero and finite temperature

    Directory of Open Access Journals (Sweden)

    Reinhardt H.

    2017-01-01

    Full Text Available I report on recent results obtained within the Hamiltonian approach to QCD in Coulomb gauge. By relating the Gribov confinement scenario to the center vortex picture of confinement it is shown that the Coulomb string tension is tied to the spatial string tension. For the quark sector a vacuum wave functional is used which results in variational equations which are free of ultraviolet divergences. The variational approach is extended to finite temperatures by compactifying a spatial dimension. For the chiral and deconfinement phase transition pseudo-critical temperatures of 170MeV and 198 MeV, respectively, are obtained.

  5. Chiral-symmetry restoration at finite densities in Coulomb-gauge QCD

    International Nuclear Information System (INIS)

    Kocic, A.

    1986-01-01

    Using the Schwinger-Dyson equation in the Hartree-Fock approximation, we show that, within a potential model motivated by the QCD Hamiltonian in the Coulomb gauge, chiral symmetry is restored at finite densities. Two cases are studied: a delta-function potential and a linear confining potential. For the former case the phase diagram is obtained analytically, whereas for the latter case numerical techniques are used. The values of physical quantities calculated for the linear confining model are consistently smaller than the experimental ones indicating that a potential with additional short-range attraction is needed to describe the quark interaction in the high-density regime

  6. Hamiltonian approach to QCD in Coulomb gauge: From the vacuum to finite temperatures

    Directory of Open Access Journals (Sweden)

    Reinhardt H.

    2016-01-01

    Full Text Available The variational Hamiltonian approach to QCD in Coulomb gauge is reviewedand the essential results obtained in recent years are summarized. First the results for thevacuum sector are discussed, with a special emphasis on the mechansim of confinementand chiral symmetry breaking. Then the deconfinement phase transition is described byintroducing temperature in the Hamiltonian approach via compactification of one spatialdimension. The effective action for the Polyakov loop is calculated and the order of thephase transition as well as the critical temperatures are obtained for the color group SU(2 and SU(3. In both cases, our predictions are in good agreement with lattice calculations.

  7. Aspects of confinement in a functional approach to coulomb gauge QCD

    International Nuclear Information System (INIS)

    Lichtenegger, K. G.

    2010-01-01

    The topic of this thesis are aspects of the confinement phenomenon in Coulomb gauge Quantum Chromodynamics.First we investigated the quark gap equation with an infrared-divergent Coulomb gluon propagator D00. As an extension to studies performed so far, some forms of an infrared-divergent spatial quark-gluon vertex have been tested, but the results remain inconclusive. There is, however, considerable evidence that some infrared dressing is required in order to obtain quantitatively reliable results. The numerical studies performed in this thesis indicate that neither the vertex form derived from the approximate Abelian Ward-Takahashi identity nor a globally divergent vertex is fit for this purpose.In addition, finite-temperature studies of pure gauge theory have been performed: On the one hand the Gribov-Zwanziger approach has been extended to the deconfined phase of Yang-Mills theory. The resulting equation has been solved numerically, which yields the Gribov mass. From this, the free energy, the interaction measure and the bulk viscosity have been determined. On the other hand, the asymptotic infrared behaviour of Dyson-Schwinger equations in Coulomb gauge have been analyzed. They yield a more than linearly rising potential for three spatial dimensions. A result which has yet to be understood.Apart from the two main topics, this thesis contains a pedagogic presentation of some peculiarities of non-Abelian gauge theories and several smaller conjectures and findings: This includes a proposal to systematize the set of gauges by introduction of an approriate metric, a discussion of the role of interpolating gauges and the use of to non-integrable potentials as well as a general expression for the number of components in the tensor decomposition of arbitrary Green functions. (author) [de

  8. Renormalizable Non-Covariant Gauges and Coulomb Gauge Limit

    CERN Document Server

    Baulieu, L

    1999-01-01

    To study ``physical'' gauges such as the Coulomb, light-cone, axial or temporal gauge, we consider ``interpolating'' gauges which interpolate linearly between a covariant gauge, such as the Feynman or Landau gauge, and a physical gauge. Lorentz breaking by the gauge-fixing term of interpolating gauges is controlled by extending the BRST method to include not only the local gauge group, but also the global Lorentz group. We enumerate the possible divergences of interpolating gauges, and show that they are renormalizable, and we show that the expectation value of physical observables is the same as in a covariant gauge. In the second part of the article we study the Coulomb-gauge as the singular limit of the Landau-Coulomb interpolating gauge. We find that unrenormalized and renormalized correlation functions are finite in this limit. We also find that there are finite two-loop diagrams of ``unphysical'' particles that are not present in formal canonical quantization in the Coulomb gauge. We verify that in the ...

  9. Many-Body Coulomb Gauge Exotic and Charmed Hybrids

    OpenAIRE

    Llanes-Estrada, Felipe J.; Cotanch, Stephen R.

    2000-01-01

    Utilizing a QCD Coulomb gauge Hamiltonian with linear confinement specified by lattice, we report a relativistic many-body calculation for the light exotic and charmed hybrid mesons. The Hamiltonian successfully describes both quark and gluon sectors, with vacuum and quasiparticle properties generated by a BCS transformation and more elaborate TDA and RPA diagonalizations for the meson ($q\\bar{q}$) and glueball ($gg$) masses. Hybrids entail a computationally intense relativistic three quasipa...

  10. Adventures in Coulomb Gauge

    International Nuclear Information System (INIS)

    Greensite, J.; Olejnik, S.

    2003-01-01

    We study the phase structure of SU(2) gauge theories at zero and high temperature, with and without scalar matter fields, in terms of the symmetric/broken realization of the remnant gauge symmetry which exists after fixing to Coulomb gauge. The symmetric realization is associated with a linearly rising color Coulomb potential (which we compute numerically), and is a necessary but not sufficient condition for confinement.

  11. Non-perturbative RPA-method implemented in the Coulomb gauge QCD Hamiltonian: From quarks and gluons to baryons and mesons

    Science.gov (United States)

    Yepez-Martinez, Tochtli; Civitarese, Osvaldo; Hess, Peter O.

    2018-02-01

    Starting from an algebraic model based on the QCD-Hamiltonian and previously applied to study meson states, we have developed an extension of it in order to explore the structure of baryon states. In developing our approach we have adapted concepts taken from group theory and non-perturbative many-body methods to describe states built from effective quarks and anti-quarks degrees of freedom. As a Hamiltonian we have used the QCD Hamiltonian written in the Coulomb Gauge, and expressed it in terms of effective quark-antiquark, di-quarks and di-antiquark excitations. To gain some insights about the relevant interactions of quarks in hadronic states, the Hamiltonian was approximately diagonalized by mapping quark-antiquark pairs and di-quarks (di-antiquarks) onto phonon states. In dealing with the structure of the vacuum of the theory, color-scalar and color-vector states are introduced to account for ground-state correlations. While the use of a purely color-scalar ground state is an obvious choice, so that colorless hadrons contain at least three quarks, the presence of coupled color-vector pairs in the ground state allows for colorless excitations resulting from the action of color objects upon it.

  12. Asymptotic freedom in the axial and Coulomb gauges

    International Nuclear Information System (INIS)

    Frenkel, J.; Taylor, J.C.

    1976-01-01

    The sources of the negative contribution to the charge renormalization factor gsup(B)/g-1 in Yang-Mills theories are investigated in the axial and Coulomb gauges. In the axial gauge, a Kaellen dispersion relation exists but the spectral function is not positive definite because of the prescription that is used to integrate the singular polarization vectors. In the Coulomb gauge, the negative contributions are (to the lowest order) isolated in the Coulomb self-energy corrections to the Coulomb field. (Auth.)

  13. Hidden QCD in Chiral Gauge Theories

    DEFF Research Database (Denmark)

    Ryttov, Thomas; Sannino, Francesco

    2005-01-01

    The 't Hooft and Corrigan-Ramond limits of massless one-flavor QCD consider the two Weyl fermions to be respectively in the fundamental representation or the two index antisymmetric representation of the gauge group. We introduce a limit in which one of the two Weyl fermions is in the fundamental...... representation and the other in the two index antisymmetric representation of a generic SU(N) gauge group. This theory is chiral and to avoid gauge anomalies a more complicated chiral theory is needed. This is the generalized Georgi-Glashow model with one vector like fermion. We show that there is an interesting...... phase in which the considered chiral gauge theory, for any N, Higgses via a bilinear condensate: The gauge interactions break spontaneously to ordinary massless one-flavor SU(3) QCD. The additional elementary fermionic matter is uncharged under this SU(3) gauge theory. It is also seen that when...

  14. Dimensional regularization and renormalization of Coulomb gauge quantum electrodynamics

    International Nuclear Information System (INIS)

    Heckathorn, D.

    1979-01-01

    Quantum electrodynamics is renormalized in the Coulomb gauge with covariant counter terms and without momentum-dependent wave-function renormalization constants. It is shown how to dimensionally regularize non-covariant integrals occurring in this guage, and prove that the 'minimal' subtraction prescription excludes non-covariant counter terms. Motivated by the need for a renormalized Coulomb gauge formalism in certain practical calculations, the author introduces a convenient prescription with physical parameters. The renormalization group equations for the Coulomb gauge are derived. (Auth.)

  15. Vacuum structure of the SU(3) gauge field theory in the Coulomb gauge

    International Nuclear Information System (INIS)

    Yee, J.H.; Viswanathan, K.S.

    1978-01-01

    The SU(3) gauge field is studied in the Coulomb gauge. The Gribov ambiguities arising in the Coulomb gauge are analysed. Restricting to a class of spherically symmetric vacua it is shown that there exist non-trivial vacua characterized by a topological number eta=0, +-1/2, and +-2. This must be contrasted with the spherically symmetric SU(2) vacua which are characterized by eta=0, +-1/2. (Auth.)

  16. Gauge orbits and the Coulomb potential

    International Nuclear Information System (INIS)

    Greensite, J.

    2009-01-01

    If the color Coulomb potential is confining, then the Coulomb field energy of an isolated color charge is infinite on an infinite lattice, even if the usual UV divergence is lattice regulated. A simple criterion for Coulomb confinement is that the expectation value of timelike link variables vanishes in the Coulomb gauge, but it is unclear how this criterion is related to the spectrum of the corresponding Faddeev-Popov operator, which can be used to formulate a quite different criterion for Coulomb confinement. The purpose of this article is to connect the two seemingly different Coulomb confinement criteria, and explain the geometrical basis of the connection.

  17. Yang-Mills theory in Coulomb gauge; Yang-Mills-theorie in Coulombeichung

    Energy Technology Data Exchange (ETDEWEB)

    Feuchter, C.

    2006-07-01

    In this thesis we study the Yang-Mills vacuum structure by using the functional Schroedinger picture in Coulomb gauge. In particular we discuss the scenario of colour confinement, which was originally formulated by Gribov. After a short introduction, we recall some basic aspects of Yang-Mills theories, its canonical quantization in the Weyl gauge and the functional Schroedinger picture. We then consider the minimal Coulomb gauge and the Gribov problem of the gauge theory. The gauge fixing of the Coulomb gauge is done by using the Faddeev-Popov method, which enables the resolution of the Gauss law - the constraint on physical states. In the third chapter, we variationally solve the stationary Yang-Mills Schroedinger equation in Coulomb gauge for the vacuum state. Therefor we use a vacuum wave functional, which is strongly peaked at the Gribov horizon. The vacuum energy functional is calculated and minimized resulting in a set of coupled Schwinger-Dyson equations for the gluon energy, the ghost and Coulomb form factors and the curvature in gauge orbit space. Using the angular approximation these integral equations have been solved analytically in both the infrared and the ultraviolet regime. The asymptotic analytic solutions in the infrared and ultraviolet regime are reasonably well reproduced by the full numerical solutions of the coupled Schwinger-Dyson equations. In the fourth chapter, we investigate the dependence of the Yang-Mills wave functional in Coulomb gauge on the Faddeev-Popov determinant. (orig.)

  18. Generalized Coulomb gauge without Gribov ambiguity

    Energy Technology Data Exchange (ETDEWEB)

    Fachin, S.; Parrinello, C. (New York Univ., NY (United States). Physics Dept.)

    1992-05-01

    We discuss a global gauge-fixing prescription that is free of the Gribov problem, preserves reflection positivity and contains as a limiting case the (maximal) Coulomb gauge. In such a formalism it is very easy to check that only color singlet states propagate in Euclidean time, for any value of [beta]. (orig.).

  19. The gauge-independent QCD effective charge

    International Nuclear Information System (INIS)

    Watson, N.J.

    1999-01-01

    It is shown how the QCD concept of a gauge-, scale-and scheme-independent one-loop effective charge can be extended directly at the diagrammatic level to QCD, thus justifying explicitly the 'naive non-abelialization' prescription used in renormalon calculus. It is first argued that, for one-shell external fields and at the strictly one-loop level, the required gluon self-energy-like function is precisely that obtained from S-matrix elements via the pinch technique. The generalization of the pinch technique to explicitly off-shell processes is then introduced. It is shown how, as a result of a fundamental cancellation among conventional perturbation theory diagrams encoded in the QCD Ward identities, the pinch technique one-loop gluon self-energy iΠ μν ab (q) remains gauge-independent and universal regardless of the fact that the 'external' fields in the given process are off-shell. This demonstration involves a simple technique enabling the isolation in a arbitrary gauge, of iΠ μν ab (q) from subclasses of up to several hundreds diagrams at once. Furthermore, it is shown how this one-loop cancellation mechanism iterates for the subclasses of n-loop diagrams containing implicitly the Dyson chains of n-loop self energies iΠ μν ab (q). The gauge cancellation required for the Dyson summation of iΠ μν ab (q) is thus demonstrated explicitly in the class of ghost-free gauges for all orders n. (authors)

  20. Questions of quark confinement and ambiguities in Coulomb gauge of Yang-Mills fields

    International Nuclear Information System (INIS)

    Abarbanel, H.D.I.; Bartels, J.

    1978-01-01

    The ambiguities considered by Gribov in the formulation of Coulomb gauge in non-Abelian gauge theories are discussed and the division of gauge field space into a sector with a unique transverse gauge, a sector with a two-fold ambiguity in transverse gauge, etc. is reviewed. The authors argue in a semi-classical fashion that transitions between these sectors readily occur and discuss the connection with ideas of quark confinement in Coulomb gauge. Because of these transitions it appears that the functional integral formulation of Coulomb gauge will be rather more complicated than expected in the past. (Auth.)

  1. Spectral sum for the color-Coulomb potential in SU(3) Coulomb gauge lattice Yang-Mills theory

    International Nuclear Information System (INIS)

    Nakagawa, Y.; Nakamura, A.; Saito, T.; Toki, H.

    2010-01-01

    We discuss the essential role of the low-lying eigenmodes of the Faddeev-Popov (FP) ghost operator on the confining color-Coulomb potential using SU(3) quenched lattice simulations in the Coulomb gauge. The color-Coulomb potential is expressed as a spectral sum of the FP ghost operator and has been explored by partially summing the FP eigenmodes. We take into account the Gribov copy effects that have a great impact on the FP eigenvalues and the color-Coulomb potential. We observe that the lowest eigenvalue vanishes in the thermodynamic limit much faster than that in the Landau gauge. The color-Coulomb potential at large distances is governed by the near-zero FP eigenmodes; in particular, the lowest one accounts for a substantial portion of the color-Coulomb string tension comparable to the Wilson string tension.

  2. Volume independence in large Nc QCD-like gauge theories

    International Nuclear Information System (INIS)

    Kovtun, Pavel; Uensal, Mithat; Yaffe, Laurence G.

    2007-01-01

    Volume independence in large N c gauge theories may be viewed as a generalized orbifold equivalence. The reduction to zero volume (or Eguchi-Kawai reduction) is a special case of this equivalence. So is temperature independence in confining phases. A natural generalization concerns volume independence in 'theory space' of quiver gauge theories. In pure Yang-Mills theory, the failure of volume independence for sufficiently small volumes (at weak coupling) due to spontaneous breaking of center symmetry, together with its validity above a critical size, nicely illustrate the symmetry realization conditions which are both necessary and sufficient for large N c orbifold equivalence. The existence of a minimal size below which volume independence fails also applies to Yang-Mills theory with antisymmetric representation fermions [QCD(AS)]. However, in Yang-Mills theory with adjoint representation fermions [QCD(Adj)], endowed with periodic boundary conditions, volume independence remains valid down to arbitrarily small size. In sufficiently large volumes, QCD(Adj) and QCD(AS) have a large N c ''orientifold'' equivalence, provided charge conjugation symmetry is unbroken in the latter theory. Therefore, via a combined orbifold-orientifold mapping, a well-defined large N c equivalence exists between QCD(AS) in large, or infinite, volume and QCD(Adj) in arbitrarily small volume. Since asymptotically free gauge theories, such as QCD(Adj), are much easier to study (analytically or numerically) in small volume, this equivalence should allow greater understanding of large N c QCD in infinite volume

  3. Renormalization of Hamiltonian QCD

    International Nuclear Information System (INIS)

    Andrasi, A.; Taylor, John C.

    2009-01-01

    We study to one-loop order the renormalization of QCD in the Coulomb gauge using the Hamiltonian formalism. Divergences occur which might require counter-terms outside the Hamiltonian formalism, but they can be cancelled by a redefinition of the Yang-Mills electric field.

  4. Hamiltonian approach to 1 + 1 dimensional Yang-Mills theory in Coulomb gauge

    International Nuclear Information System (INIS)

    Reinhardt, H.; Schleifenbaum, W.

    2009-01-01

    We study the Hamiltonian approach to 1 + 1 dimensional Yang-Mills theory in Coulomb gauge, considering both the pure Coulomb gauge and the gauge where in addition the remaining constant gauge field is restricted to the Cartan algebra. We evaluate the corresponding Faddeev-Popov determinants, resolve Gauss' law and derive the Hamiltonians, which differ in both gauges due to additional zero modes of the Faddeev-Popov kernel in the pure Coulomb gauge. By Gauss' law the zero modes of the Faddeev-Popov kernel constrain the physical wave functionals to zero colour charge states. We solve the Schroedinger equation in the pure Coulomb gauge and determine the vacuum wave functional. The gluon and ghost propagators and the static colour Coulomb potential are calculated in the first Gribov region as well as in the fundamental modular region, and Gribov copy effects are studied. We explicitly demonstrate that the Dyson-Schwinger equations do not specify the Gribov region while the propagators and vertices do depend on the Gribov region chosen. In this sense, the Dyson-Schwinger equations alone do not provide the full non-abelian quantum gauge theory, but subsidiary conditions must be required. Implications of Gribov copy effects for lattice calculations of the infrared behaviour of gauge-fixed propagators are discussed. We compute the ghost-gluon vertex and provide a sensible truncation of Dyson-Schwinger equations. Approximations of the variational approach to the 3 + 1 dimensional theory are checked by comparison to the 1 + 1 dimensional case

  5. The three-point function in split dimensional regularization in the Coulomb gauge

    CERN Document Server

    Leibbrandt, G

    1998-01-01

    We use a gauge-invariant regularization procedure, called ``split dimensional regularization'', to evaluate the quark self-energy $\\Sigma (p)$ and quark-quark-gluon vertex function $\\Lambda_\\mu (p^\\prime,p)$ in the Coulomb gauge, $\\vec{\\bigtriangledown}\\cdot\\vec{A}^a = 0$. The technique of split dimensional regularization was designed to regulate Coulomb-gauge Feynman integrals in non-Abelian theories. The technique which is based on two complex regulating parameters, $\\omega$ and $\\sigma$, is shown to generate a well-defined set of Coulomb-gauge integrals. A major component of this project deals with the evaluation of four-propagator and five-propagator Coulomb integrals, some of which are nonlocal. It is further argued that the standard one-loop BRST identity relating $\\Sigma$ and $\\Lambda_\\mu$, should by rights be replaced by a more general BRST identity which contains two additional contributions from ghost vertex diagrams. Despite the appearance of nonlocal Coulomb integrals, both $\\Sigma$ and $\\Lambda_\\...

  6. The three-point function in split dimensional regularization in the Coulomb gauge

    International Nuclear Information System (INIS)

    Leibbrandt, G.

    1998-01-01

    We use a gauge-invariant regularization procedure, called split dimensional regularization, to evaluate the quark self-energy Σ(p) and quark-quark-gluon vertex function Λ μ (p',p) in the Coulomb gauge, ∇-vector.A - vectora=0. The technique of split dimensional regularization was designed to regulate Coulomb-gauge Feynman integrals in non-Abelian theories. The technique which is based on two complex regulating parameters, ω and σ, is shown to generate a well-defined set of Coulomb-gauge integrals. A major component of this project deals with the evaluation of four-propagator and five-propagator Coulomb integrals, some of which are non-local. It is further argued that the standard one-loop BRST identity relating Σ and Λ μ , should by rights be replaced by a more general BRST identity which contains two additional contributions from ghost vertex diagrams. Despite the appearance of non-local Coulomb integrals, both Σ and Λ μ are local functions which satisfy the appropriate BRST identity. Application of split dimensional regularization to two-loop energy integrals is briefly discussed. (orig.)

  7. The gauge-independent QCD effective charge

    International Nuclear Information System (INIS)

    Watson, N.J.

    1997-01-01

    It is shown how the QED concept of a gauge-, scale- and scheme-independent one-loop effective charge can be extended directly at the diagrammatic level to QCD, thus justifying explicitly the ''naive non-abelianization'' prescription used in renormalon calculus. It is first argued that, for on-shell external fields and at the strictly one-loop level, the required gluon self-energy-like function is precisely that obtained from S-matrix elements via the pinch technique. The generalization of the pinch technique to explicitly off-shell processes is then introduced. It is shown how, as a result of a fundamental cancellation among conventional perturbation theory diagrams, encoded in the QCD Ward identities, the pinch technique one-loop gluon self-energy iΠ μν ab (q) remains gauge-independent and universal regardless of the fact that the ''external'' fields in the given process are off-shell. This demonstration involves a simple technique enabling the isolation, in an arbitrary gauge, of iΠ μν ab (q) from subclasses of up to several hundred diagrams at once. Furthermore, it is shown how this one-loop cancellation mechanism iterates for the subclasses of n-loop diagrams containing implicitly the Dyson chains of n one-loop self-energies iΠ μν ab (q). The gauge cancellation required for the Dyson summation of iΠ μν ab (q) is thus demonstrated explicitly in a general class of ghost-free gauges for all orders n. (orig.)

  8. Gauge/String Duality, Hot QCD and Heavy Ion Collisions

    CERN Document Server

    Casalderrey-Solana, Jorge; Mateos, David; Rajagopal, Krishna; Wiedemann, Urs Achim

    2011-01-01

    Over the last decade, both experimental and theoretical advances have brought the need for strong coupling techniques in the analysis of deconfined QCD matter and heavy ion collisions to the forefront. As a consequence, a fruitful interplay has developed between analyses of strongly-coupled non-abelian plasmas via the gauge/string duality (also referred to as the AdS/CFT correspondence) and the phenomenology of heavy ion collisions. We review some of the main insights gained from this interplay to date. To establish a common language, we start with an introduction to heavy ion phenomenology and finite-temperature QCD, and a corresponding introduction to important concepts and techniques in the gauge/string duality. These introductory sections are written for nonspecialists, with the goal of bringing readers ranging from beginning graduate students to experienced practitioners of either QCD or gauge/string duality to the point that they understand enough about both fields that they can then appreciate their in...

  9. Factorization in QCD in Feynman gauge

    International Nuclear Information System (INIS)

    Tucci, R.R.

    1985-01-01

    We present a mass divergence power counting technique for QCD in the Feynman gauge. For the process γ/sup */ → qq, we find the leading regions of integration and show that single diagrams are at worst logarithmically divergent. Using the Weyl representation facilities the γ matrix manipulations necessary for power counting and adds much physical insight. We prove Ward type identities which are needed in the proof of factorization of the Drill Yan process. Previous treatments prove them only for an axial gauge, and the proofs are diagrammatic in nature. We, on the other hand, establish the identities for the Feynman gauge and through symmetry considerations at the Lagrangian level. The strategy is to first derive exact results in a background field gauge and then to show that to leading order in the mass divergences the background field gauge results can be used in the Feynman gauge

  10. Confinement in Polyakov gauge and the QCD phase diagram

    Energy Technology Data Exchange (ETDEWEB)

    Marhauser, Marc Florian

    2009-10-14

    We investigate Quantum Chromodynamics (QCD) in the framework of the functional renormalisation group (fRG). Thereby describing the phase transition from the phase with confined quarks into the quark-gluon-plasma phase. We focus on a physical gauge in which the mechanism driving the phase transition is discernible. We find results compatible with lattice QCD data, as well as with functional methods applied in different gauges. The phase transition is of the expected order and we computed critical exponents. Extensions of the model are discussed. When investigating the QCD phase diagram, we compute the effects of dynamical quarks at finite density on the running of the gauge coupling. Additionally, we calculate how these affect the deconfinement phase transition, also, dynamical quarks allow for the inclusion of a finite chemical potential. Concluding the investigation of the phase diagram, we establish a relation between confinement and chiral symmetry breaking, which is tied to the dynamical generation of hadron masses. In the investigations, we often encounter scale dependent fields. We investigate a footing on which these can be dealt with in a uniform way. (orig.)

  11. The Yang-Mills vacuum wave functional in Coulomb gauge

    International Nuclear Information System (INIS)

    Campagnari, Davide R.

    2011-01-01

    Yang-Mills theories are the building blocks of today's Standard Model of elementary particle physics. Besides methods based on a discretization of space-time (lattice gauge theory), also analytic methods are feasible, either in the Lagrangian or in the Hamiltonian formulation of the theory. This thesis focuses on the Hamiltonian approach to Yang-Mills theories in Coulomb gauge. The thesis is presented in cumulative form. After an introduction into the general formulation of Yang-Mills theories, the Hamilton operator in Coulomb gauge is derived. Chap. 1 deals with the heat-kernel expansion of the Faddeev-Popov determinant. In Chapters 2 and 3, the high-energy behaviour of the theory is investigated. To this purpose, perturbative methods are applied, and the results are compared with the ones stemming from functional methods in Coulomb and Landau gauge. Chap. 4 is devoted to the variational approach. Variational ansatzes going beyond the Gaussian form for the vacuum wave functional are considered and treated using Dyson-Schwinger techniques. Equations for the higher-order variational kernels are derived and their effects are estimated. Chap. 5 presents an application of the previously obtained propagators, namely the evaluation of the topological susceptibility, which is related to the mass of the η meson. Finally, a short overview of the perturbative treatment of dynamical fermion fields is presented.

  12. Ice limit of Coulomb gauge Yang-Mills theory

    International Nuclear Information System (INIS)

    Heinzl, T.; Ilderton, A.; Langfeld, K.; Lavelle, M.; McMullan, D.

    2008-01-01

    In this paper we describe gauge invariant multiquark states generalizing the path integral framework developed by Parrinello, Jona-Lasinio, and Zwanziger to amend the Faddeev-Popov approach. This allows us to produce states such that, in a limit which we call the ice limit, fermions are dressed with glue exclusively from the fundamental modular region associated with Coulomb gauge. The limit can be taken analytically without difficulties, avoiding the Gribov problem. This is illustrated by an unambiguous construction of gauge invariant mesonic states for which we simulate the static quark-antiquark potential.

  13. Hamiltonian formulation of QCD in the Schwinger gauge

    International Nuclear Information System (INIS)

    Schutte, D.

    1989-01-01

    The structure of the Hamiltonian related to a regularized non-Abelian gauge field theory is discussed in the light of different choices for gauge-invariant wave functionals (loop space, Coulomb, axial, Schwinger gauge). Arguments are given for the suggestion that the Schwinger gauge offers a specially suited framework for the computation of bound-state (hadron) properties. The most important reasons are the manifest rotation invariance, the lack of a Gribov horizon (giving standard many-body techniques a better chance), and the fact that a regularization analogous to the lattice regularization is easily implementable. Some details of the Schwinger-gauge Hamiltonian theory are discussed

  14. Quasineutral Limit of the Schrödinger-Poisson System in Coulomb Gauge

    OpenAIRE

    Lin, Chi-Kun; Wong, Yau-Shu; Wu, Kung-Chien

    2012-01-01

    The zero Debye length asymptotic of the Schrödinger-Poisson system in Coulomb gauge for ill-prepared initial data is studied. We prove that when the scaled Debye length λ → 0, the current density defined by the solution of the Schrödinger-Poisson system in the Coulomb gauge converges to the solution of the rotating incompressible Euler equation plus a fast singular oscillating gradient vector field.

  15. Leading non-cancelling infra-red divergences in perturbative QCD

    International Nuclear Information System (INIS)

    Carneiro, C.E.; Frenkel, J.; Thomaz, M.T.; Day, M.; Taylor, J.C.

    1980-01-01

    In QCD in perturbative theory, for the inclusive cross-section for the scattering of two coloured particles, graphs which contribute to the general leading order αs(αs/nΛ)(sup n) are identified and these contributions are added (Λ is the IR cut-off). The work is done in the Coulomb gauge; an appendix discusses the Feynman gauge. (Author) [pt

  16. Gravitationally induced zero modes of the Faddeev-Popov operator in the Coulomb gauge for Abelian gauge theories

    Science.gov (United States)

    Canfora, Fabrizio; Giacomini, Alex; Oliva, Julio

    2010-08-01

    It is shown that on curved backgrounds, the Coulomb gauge Faddeev-Popov operator can have zero modes even in the Abelian case. These zero modes cannot be eliminated by restricting the path integral over a certain region in the space of gauge potentials. The conditions for the existence of these zero modes are studied for static spherically symmetric spacetimes in arbitrary dimensions. For this class of metrics, the general analytic expression of the metric components in terms of the zero modes is constructed. Such expression allows one to find the asymptotic behavior of background metrics, which induce zero modes in the Coulomb gauge, an interesting example being the three-dimensional anti-de Sitter spacetime. Some of the implications for quantum field theory on curved spacetimes are discussed.

  17. Maxwell-Chern-Simons theory in covariant and Coulomb gauges

    International Nuclear Information System (INIS)

    Haller, K.; Lim-Lombridas, E.

    1996-01-01

    We quantize quantum electrodynamics in 2 + 1 dimensions coupled to a Chern-Simons (CS) term and a charged spinor field, in covariant gauges and in the Coulomb gauge. The resulting Maxwell-Chern-Simons (MCS) theory describes charged fermions interacting with each other and with topologically massive propagating photons. We impose Gauss's law and the gauge conditions and investigate their effect on the dynamics and on the statistics of n-particle states. We construct charged spinor states that obey Gauss's law and the gauge conditions and transform the theory to representations in which these states constitute a Fock space. We demonstrate that, in these representations, the nonlocal interactions between charges and between charges and transverse currents-along with the interactions between currents and massive propagating photons-are identical in the different gauges we analyze in this and in earlier work. We construct the generators of the Poincare group, show that they implement the Poincare algebra, and explicitly demonstrate the effect of rotations and Lorentz boosts on the particle states. We show that the imposition of Gauss's law does not produce any open-quotes exoticclose quotes fractional statistics. In the case of the covariant gauges, this demonstration makes use of unitary transformations that provide charged particles with the gauge fields required by Gauss's law, but that leave the anticommutator algebra of the spinor fields untransformed. In the Coulomb gauge, we show that the anticommutators of the spinor fields apply to the Dirac-Bergmann constraint surfaces, on which Gauss's law and the gauge conditions obtain. We examine MCS theory in the large CS coupling constant limit, and compare that limiting form with CS theory, in which the Maxwell kinetic energy term is not included in the Larangian. 34 refs

  18. A further pathology of the Coulomb gauge in non-Abelian Yang-Mills theories

    International Nuclear Information System (INIS)

    Ademollo, M.; Napolitano, E.; Sciuto, S.

    1978-01-01

    In the first part the vacuum structure of SU(2) Yang-Mills theories in the Coulomb gauge is discussed. It is proved that the only transverse pure gauge field Asub(μ)(x) = U -1 deltasub(μ)U with U(x) → (as r→infinity) const., is the trivial one Asub(μ)(x) equivalent to 0; the features of other possible vacua with U(x) → (as r→infinity) U(theta, pli) are studied. In the second part, regular Euclidean configurations that connect a vacuum state at x 4 = -infinity to another at x 4 = +infinity are discussed. It is proved, always working in the Coulomb gauge, that the perturbative vacuum Asub(μ)(x) equivalent to 0 cannot tunnel into any other one and that regular configurations with non-vanishing Pontryagin number q cannot affect such a vacuum. Moreover, strong arguments are given to show that many-instanton configurations (mod(q)>=2) cannot be expressed at all in the Coulomb gauge, that is by a regular field Asub(μ) satisfying the transversality condition deltasub(i)Asub(i) (x, x 4 ) = 0. (Auth.)

  19. Monopole operators and Hilbert series of Coulomb branches of 3 d = 4 gauge theories

    Science.gov (United States)

    Cremonesi, Stefano; Hanany, Amihay; Zaffaroni, Alberto

    2014-01-01

    This paper addresses a long standing problem - to identify the chiral ring and moduli space (i.e. as an algebraic variety) on the Coulomb branch of an = 4 superconformal field theory in 2+1 dimensions. Previous techniques involved a computation of the metric on the moduli space and/or mirror symmetry. These methods are limited to sufficiently small moduli spaces, with enough symmetry, or to Higgs branches of sufficiently small gauge theories. We introduce a simple formula for the Hilbert series of the Coulomb branch, which applies to any good or ugly three-dimensional = 4 gauge theory. The formula counts monopole operators which are dressed by classical operators, the Casimir invariants of the residual gauge group that is left unbroken by the magnetic flux. We apply our formula to several classes of gauge theories. Along the way we make various tests of mirror symmetry, successfully comparing the Hilbert series of the Coulomb branch with the Hilbert series of the Higgs branch of the mirror theory.

  20. A preliminary study of the Gribov ambiguity in lattice SU(3) Coulomb gauge

    Energy Technology Data Exchange (ETDEWEB)

    Parrinello, C. (Physics Dept., New York Univ., NY (United States)); Petrarca, S. (Dipt. di Fisica, Rome-1 Univ. (Italy) INFN, Rome (Italy)); Vladikas, A. (Dipt. di Fisica, Rome-2 Univ. (Italy) INFN, Rome (Italy))

    1991-10-10

    We report on simulations of pure SU(3) gauge theory on a 10{sup 3}x20 lattice at {beta}=6.0 in the Coulomb gauge, from which the Gribov ambiguity appears to be maximal, in the sense that the gauge-fixing process is highly unstable with respect to variations of the starting configuration via random gauge transformations. We give a heuristic explanation of the larger number of Gribov copies in such a gauge with respect to the Landau gauge. (orig.).

  1. The ghost propagator in Coulomb gauge

    International Nuclear Information System (INIS)

    Watson, P.; Reinhardt, H.

    2011-01-01

    We present results for a numerical study of the ghost propagator in Coulomb gauge whereby lattice results for the spatial gluon propagator are used as input to solving the ghost Dyson-Schwinger equation. We show that in order to solve completely, the ghost equation must be supplemented by a boundary condition (the value of the inverse ghost propagator dressing function at zero momentum) which determines if the solution is critical (zero value for the boundary condition) or subcritical (finite value). The various solutions exhibit a characteristic behavior where all curves follow the same (critical) solution when going from high to low momenta until 'forced' to freeze out in the infrared to the value of the boundary condition. The boundary condition can be interpreted in terms of the Gribov gauge-fixing ambiguity; we also demonstrate that this is not connected to the renormalization. Further, the connection to the temporal gluon propagator and the infrared slavery picture of confinement is discussed.

  2. Localizing gauge fields on a topological Abelian string and the Coulomb law

    International Nuclear Information System (INIS)

    Torrealba S, Rafael S.

    2010-01-01

    The confinement of electromagnetic field is studied in axial symmetrical, warped, six-dimensional brane world, using a recently proposed topological Abelian string-vortex solution as background. It was found, that the massless gauge field fluctuations follow four-dimensional Maxwell equations in the Lorenz gauge. The massless zero mode is localized when the thickness of the string vortex is less than 5β/4πe 2 v 2 and there are no other localized massless modes. There is also an infinite of nonlocalized massive Fourier modes, that follow four-dimensional Proca equations with a continuous spectrum. To compute the corrections to the Coulomb potential, a radial cutoff was introduced, in order to achieve a discrete mass spectrum. As a main result, a (R o /βR 2 ) correction was found for the four-dimensional effective Coulomb law; the result is in correspondence with the observed behavior of the Coulomb potential at today's measurable distances.

  3. Coulomb branches for rank 2 gauge groups in 3dN=4 gauge theories

    Energy Technology Data Exchange (ETDEWEB)

    Hanany, Amihay [Theoretical Physics Group, Imperial College London,Prince Consort Road, London, SW7 2AZ (United Kingdom); Sperling, Marcus [Institut für Theoretische Physik, Leibniz Universität Hannover,Appelstraße 2, 30167 Hannover (Germany)

    2016-08-02

    The Coulomb branch of 3-dimensional N=4 gauge theories is the space of bare and dressed BPS monopole operators. We utilise the conformal dimension to define a fan which, upon intersection with the weight lattice of a GNO-dual group, gives rise to a collection of semi-groups. It turns out that the unique Hilbert bases of these semi-groups are a sufficient, finite set of monopole operators which generate the entire chiral ring. Moreover, the knowledge of the properties of the minimal generators is enough to compute the Hilbert series explicitly. The techniques of this paper allow an efficient evaluation of the Hilbert series for general rank gauge groups. As an application, we provide various examples for all rank two gauge groups to demonstrate the novel interpretation.

  4. Instanton effects in three-dimensional supersymmetric gauge theories with matter

    NARCIS (Netherlands)

    Dorey, N.; Tong, D.; Vandoren, S.

    1998-01-01

    Using standard field theory techniques we compute perturbative and instanton contributions to the Coulomb branch of three-dimensional supersymmetric QCD with N = 2 and N = 4 supersymmetry and gauge group SU(2). For the N = 4 theory with one massless flavor, we confirm the proposal of Seiberg and

  5. Equivalence of the Weyl, Coulomb, unitary, and covariant gauges in the functional Schrodinger picture

    International Nuclear Information System (INIS)

    Namgung, W.

    1991-01-01

    The well known requirement that physical theories should be gauge independent is not so apparent in the actual calculation of gauge theories, especially in the perturbative approach. In this paper the authors show that the Weyl, Coulomb, and unitary gauges of the scalar QED are manifestly equivalent in the context of the functional Schrodinger picture. Further, the three gauge conditions are shown equivalent to the covariant gauge in the way that they correspond to some specific cases of the latter

  6. Heavy-heavy-light quark potential in SU(3) lattice QCD

    International Nuclear Information System (INIS)

    Yamamoto, Arata; Suganuma, Hideo; Iida, Hideaki

    2008-01-01

    We perform the first study for the heavy-heavy-light quark (QQq) potential in SU(3) quenched lattice QCD with the Coulomb gauge. The calculations are done with the standard gauge and O(a)-improved Wilson fermion action on the 16 4 lattice at β=6.0. We calculate the energy of QQq systems as the function of the distance R between the two heavy quarks, and find that the QQq potential is well described with a Coulomb plus linear potential form up to the intermediate distance R≤0.8 fm. Compared to the static three-quark case, the effective string tension between the heavy quarks is significantly reduced by the finite-mass valence quark effect. This reduction is considered to be a general property for baryons

  7. Instanton Effects in Three-Dimensional Supersymmetric Gauge Theories with Matter

    OpenAIRE

    Dorey, N.; Tong, D.; Vandoren, S.

    1998-01-01

    Using standard field theory techniques we compute perturbative and instanton contributions to the Coulomb branch of three-dimensional supersymmetric QCD with N = 2 and N = 4 supersymmetry and gauge group SU(2). For the N = 4 theory with one massless flavor, we confirm the proposal of Seiberg and Witten that the Coulomb branch is the double-cover of the centered moduli space of two BPS monopoles constructed by Atiyah and Hitchin. Introducing a hypermultiplet mass term, we show that the asympto...

  8. A short proof that the Coulomb-gauge potentials yield the retarded fields

    Energy Technology Data Exchange (ETDEWEB)

    Heras, Jose A, E-mail: herasgomez@gmail.co [Universidad Autonoma Metropolitana, Unidad Azcapotzalco, Av. San Pablo No. 180, Col. Reynosa, Mexico D. F. 02200 (Mexico)

    2011-01-15

    A short demonstration that the potentials in the Coulomb gauge yield the retarded electric and magnetic fields is presented. This demonstration is relatively simple and can be presented in an advanced undergraduate course of electromagnetic theory.

  9. A short proof that the Coulomb-gauge potentials yield the retarded fields

    International Nuclear Information System (INIS)

    Heras, Jose A

    2011-01-01

    A short demonstration that the potentials in the Coulomb gauge yield the retarded electric and magnetic fields is presented. This demonstration is relatively simple and can be presented in an advanced undergraduate course of electromagnetic theory.

  10. Sources, potentials and fields in Lorenz and Coulomb gauge: Cancellation of instantaneous interactions for moving point charges

    International Nuclear Information System (INIS)

    Wundt, B.J.; Jentschura, U.D.

    2012-01-01

    We investigate the coupling of the electromagnetic sources (charge and current densities) to the scalar and vector potentials in classical electrodynamics, using Green function techniques. As is well known, the scalar potential shows an action-at-a-distance behavior in Coulomb gauge. The conundrum generated by the instantaneous interaction has intrigued physicists for a long time. Starting from the differential equations that couple the sources to the potentials, we here show in a concise derivation, using the retarded Green function, how the instantaneous interaction cancels in the calculation of the electric field. The time derivative of a specific additional term in the vector potential, present only in Coulomb gauge, yields a supplementary contribution to the electric field which cancels the gradient of the instantaneous Coulomb gauge scalar potential, as required by gauge invariance. This completely eliminates the contribution of the instantaneous interaction from the electric field. It turns out that a careful formulation of the retarded Green function, inspired by field theory, is required in order to correctly treat boundary terms in partial integrations. Finally, compact integral representations are derived for the Liénard–Wiechert potentials (scalar and vector) in Coulomb gauge which manifestly contain two compensating action-at-a-distance terms. - Highlights: ► We investigate action-at-a-distance effects in electrodynamics in detail. ► We calculate the instantaneous interactions for scalar and vector potentials. ► The cancellation mechanism involves the retarded Green function. ► The mechanism is confirmed on the example of moving point charges. ► The Green function has to be treated with care for nontrivial boundary terms.

  11. Verification of Equivalence of the Axial Gauge to the Coulomb Gauge in QED by Embedding in the Indefinite Metric Hilbert Space : Particles and Fields

    OpenAIRE

    Yuji, NAKAWAKI; Azuma, TANAKA; Kazuhiko, OZAKI; Division of Physics and Mathematics, Faculty of Engineering Setsunan University; Junior College of Osaka Institute of Technology; Faculty of General Education, Osaka Institute of Technology

    1994-01-01

    Gauge Equivalence of the A_3=0 (axial) gauge to the Coulomb gauge is directly verified in QED. For that purpose a pair of conjugate zero-norm fields are introduced. This enables us to construct a canonical formulation in the axial gauge embedded in the indefinite metric Hilbert space in such a way that the Feynman rules are not altered. In the indefinite metric Hilbert space we can implement a gauge transformation, which otherwise has to be carried out only by hand, as main parts of a canonic...

  12. Body fixed frame, rigid gauge rotations and large N random fields in QCD

    International Nuclear Information System (INIS)

    Levit, S.

    1995-01-01

    The ''body fixed frame'' with respect to local gauge transformations is introduced. Rigid gauge ''rotations'' in QCD and their Schroedinger equation are studied for static and dynamic quarks. Possible choices of the rigid gauge field configuration corresponding to a non-vanishing static colormagnetic field in the ''body fixed'' frame are discussed. A gauge invariant variational equation is derived in this frame. For large number N of colors the rigid gauge field configuration is regarded as random with maximally random probability distribution under constraints on macroscopic-like quantities. For the uniform magnetic field the joint probability distribution of the field components is determined by maximizing the appropriate entropy under the area law constraint for the Wilson loop. In the quark sector the gauge invariance requires the rigid gauge field configuration to appear not only as a background but also as inducing an instantaneous quark-quark interaction. Both are random in the large N limit. (orig.)

  13. QCD gauge symmetries through Faddeev-Jackiw symplectic method

    International Nuclear Information System (INIS)

    Abreu, E.M.C.; Mendes, A.C.R.; Neves, C.; Oliveira, W.; Silva, R.C.N.

    2013-01-01

    Full text: The FJ method is an approach that is geometrically motivated. It is based on the symplectic structure of the phase space. The first-order characteristic allows to obtain the Hamiltonian equations of motion from a variational principle. Its geometric structure of the Hamiltonian phase-space will be carried out directly from the equations of motion via the inverse of the so-called symplectic two-form, if the inverse exists. Few years after its publication, the FJ formalism was extended and through the years it has been applied to different systems. Gauge invariance is one of the most well established concepts in theoretical physics and it is one of the main ingredients in Standard Model theory. However, we can ask if it could have an alternative origin connected to another theory or principle. With this motivation in mind we will show in this paper that gauge invariance could be considered an emergent concept having its origin in the algebraic formalism of a well known method that deals with constrained systems, namely, the Faddeev-Jackiw (FJ) technique. Of course the gauge invariance idea is older than FJ's, but the results obtained here will show that the connection between both will prove that SU(3) and SU(3) X SU(2) X U(1) gauge groups, which are fundamental to important theories like QCD and Standard Model, can be obtained through FJ formalism. (author)

  14. Lattice QCD

    International Nuclear Information System (INIS)

    Hasenfratz, P.

    1983-01-01

    The author presents a general introduction to lattice gauge theories and discusses non-perturbative methods in the gauge sector. He then shows how the lattice works in obtaining the string tension in SU(2). Lattice QCD at finite physical temperature is discussed. Universality tests in SU(2) lattice QCD are presented. SU(3) pure gauge theory is briefly dealt with. Finally, fermions on the lattice are considered. (Auth.)

  15. New Applications of Resummation in Non-Abelian Gauge Theories: QED-QCD Exponentiation for LHC Physics, IR-Improved DGLAP Theory and Resummed Quantum Gravity

    International Nuclear Information System (INIS)

    Ward, B.F.L.

    2006-01-01

    We present the elements of three applications of resummation methods in non-Abelian gauge theories: (1), QED-QCD exponentiation and shower/ME matching for LHC physics; (2), IR improvement of DGLAP theory; (3), resummed quantum gravity and the final state of Hawking radiation. In all cases, the extension of the YFS approach, originally introduced for Abelian gauge theory, to non-Abelian gauge theories, QCD and quantum general relativity, leads to new results and solutions which we briefly summarize

  16. Duality and BPS spectra in N = 2 supersymmetric QCD

    Energy Technology Data Exchange (ETDEWEB)

    Ferrari, F. [Ecole Normale Superieure, 75 - Paris (France). Lab. de Physique Theorique

    1997-05-01

    I review, with some pedagogy, two different approaches to the computation of BPS spectra in N = 2 supersymmetric QCD with gauge group SU(2). The first one is semiclassical and has been widely used in the literature. The second one makes use of constraints coming from the non perturbative, global structure of the Coulomb branch of these theories. The second method allows for a description of discontinuities in the BPS spectra at strong coupling, and should lead to accurate test of duality conjectures in N = 2 theories. (orig.).

  17. Duality and BPS spectra in N = 2 supersymmetric QCD

    International Nuclear Information System (INIS)

    Ferrari, F.

    1997-01-01

    I review, with some pedagogy, two different approaches to the computation of BPS spectra in N = 2 supersymmetric QCD with gauge group SU(2). The first one is semiclassical and has been widely used in the literature. The second one makes use of constraints coming from the non perturbative, global structure of the Coulomb branch of these theories. The second method allows for a description of discontinuities in the BPS spectra at strong coupling, and should lead to accurate test of duality conjectures in N = 2 theories. (orig.)

  18. Heavy quark free energy in QCD and in gauge theories with gravity duals

    Science.gov (United States)

    Noronha, Jorge

    2010-09-01

    Recent lattice results in pure glue SU(3) theory at high temperatures have shown that the expectation value of the renormalized Polyakov loop approaches its asymptotic limit at high temperatures from above. We show that this implies that the “heavy quark free energy” obtained from the renormalized loop computed on the lattice does not behave like a true thermodynamic free energy. While this should be expected to occur in asymptotically free gauge theories such as QCD, we use the gauge/string duality to show that in a large class of strongly coupled gauge theories with nontrivial UV fixed points the Polyakov loop reaches its asymptotic value from above only if the dimension of the relevant operator used to deform the conformal field theory is greater than or equal to 3.

  19. QCD Dual

    DEFF Research Database (Denmark)

    Sannino, Francesco

    2009-01-01

    We uncover a novel solution of the 't Hooft anomaly matching conditions for QCD. Interestingly in the perturbative regime the new gauge theory, if interpreted as a possible QCD dual, predicts the critical number of flavors above which QCD in the nonperturbative regime, develops an infrared stable...

  20. Beyond QCD: Why and How

    International Nuclear Information System (INIS)

    Preparata, G.

    1983-01-01

    In this paper the necessity of going beyond Quantum chromodynamics is argued, and a new theory of Isotropic Chromodynamics (ICD) is introduced. The basic theoretical notions behind QCD--quarks, colors, and gauge theory are retained, but the conclusion that QCD must be the theory of hadrions is questioned. Two points of QCD are reviewed, gluons (including glueballs), and asymptotic freedom. It is suggested that much of this theory is wishful thinking. Beyond QCD, aspects which are puzzling in hadrodynamics are well understood in two-dimensional gauge theories (confinement, freedom at short distances etc). Anisotropic chromodynamics is proposed in the attempt to conjugate the basic pillars of hadrodynamics with the peculiar characteristics of two-dimensional gauge dynamics. In order to construct a gauge dynamics for the color field which is isomorphic to a two-dimensional gauge-theory base space must be enlarged to a seven dimension space-time structure, to be called Anisotropic Space-Time (AST). The ideas and present achievements of ICD are then reviewed

  1. Bogoliubov condensation of gluons and spontaneous gauge symmetry breaking in QCD

    International Nuclear Information System (INIS)

    Pervushin, V.N.; Roepke, G.; Volkov, M.K.; Blaschke, D.; Pavel, H.P.; Litvin, A.

    1995-08-01

    The ''squeezed'' representation of commutation relations for gluon fields in QCD is formulated as the mathematical tool for the description of the gluon condensate. We first consider λφ 4 theory and show that the ''squeezed'' Bogoliubov condensate can lead to the spontaneous appearance of a mass. Using the ''squeezed'' representation, we show that in the non-Abelian theory spontaneous gauge symmetry breaking (SGSB) and the appearance of a constituent mass of gluons can be described. We construct a projector onto the oscillator - like variables, for which the ''squeezed'' representation is valid, by using the formal solution of the Gauss equation instead of fixing a gauge. We discuss the effects of the SGSB and present as an application of the approach the calculation of the gluon mass from the difference of the η' and the η - meson masses. (author). 27 refs

  2. Metastable vacuum decay and θ dependence in gauge theory. Deformed QCD as a toy model

    Energy Technology Data Exchange (ETDEWEB)

    Bhoonah, Amit; Thomas, Evan, E-mail: zucchini@phas.ubc.ca; Zhitnitsky, Ariel R., E-mail: arz@phas.ubc.ca

    2015-01-15

    We study a number of different ingredients related to the θ dependence, metastable excited vacuum states and other related subjects using a simplified version of QCD, the so-called “deformed QCD”. This model is a weakly coupled gauge theory, which, however, preserves all the relevant essential elements allowing us to study hard and nontrivial features which are known to be present in real strongly coupled QCD. Our main focus in this work is to test the ideas related to the metastable vacuum states (which are known to be present in strongly coupled QCD in large N limit) in a theoretically controllable manner using the “deformed QCD” as a toy model. We explicitly show how the metastable states emerge in the system, why their lifetime is large, and why these metastable states must be present in the system for the self-consistency of the entire picture of the QCD vacuum. We also speculate on possible relevance of the metastable vacuum states in explanation of the violation of local P and CP symmetries in heavy ion collisions.

  3. Metastable vacuum decay and θ dependence in gauge theory. Deformed QCD as a toy model

    International Nuclear Information System (INIS)

    Bhoonah, Amit; Thomas, Evan; Zhitnitsky, Ariel R.

    2015-01-01

    We study a number of different ingredients related to the θ dependence, metastable excited vacuum states and other related subjects using a simplified version of QCD, the so-called “deformed QCD”. This model is a weakly coupled gauge theory, which, however, preserves all the relevant essential elements allowing us to study hard and nontrivial features which are known to be present in real strongly coupled QCD. Our main focus in this work is to test the ideas related to the metastable vacuum states (which are known to be present in strongly coupled QCD in large N limit) in a theoretically controllable manner using the “deformed QCD” as a toy model. We explicitly show how the metastable states emerge in the system, why their lifetime is large, and why these metastable states must be present in the system for the self-consistency of the entire picture of the QCD vacuum. We also speculate on possible relevance of the metastable vacuum states in explanation of the violation of local P and CP symmetries in heavy ion collisions

  4. QCD inspired bag model of quarkonium

    International Nuclear Information System (INIS)

    Hasenfratz, P.; Horgan, R.R.; Kuti, J.; Richard, J.M.

    1981-01-01

    The QCD motivated bag model is applied to heavy quark-antiquark systems. The effect of colored glue in the model is shown to explain the rapid cross-over of the static QQ potential from the asymptotically free Coulomb region into the linear confinement regime. The spin-dependent force between static quarks is derived in Coulomb gauge from the exchange of a confined transverse gluon. The dimensional bag parameter Λ/sub B/ = 235 MeV and the quark-gluon coupling constant α = 0.38 as defined at r/sub QQ/approx.0.2 fermi are determined from a good fit of the cc-bar and bb-bar spectra. The fit is in serious disagreement with the widely accepted MIT parameters. As an important test of our model, we calculate the rich spectrum of QQ glue states. In UPSILON particle spectroscopy we predict a narrow QQ glue state with exotic quantum numbers J/sup PC/ = 1 -+ below the BB threshold. Its experimental confirmation would be the first direct evidence for colored glue in the hadron spectrum

  5. QCD inspired bag model of quarkonium

    CERN Document Server

    Hasenfratz, Peter; Kuti, Julius; Richard, J M

    1981-01-01

    The QCD motivated bag model is applied to heavy quark-antiquark systems. The effect of colored glue in the model is shown to explain the rapid cross-over of the static QQ potential from the asymptotically free Coulomb region into the linear confinement regime. The spin-dependent force between static quarks is derived in Coulomb gauge from the exchange of a confined transverse gluon. The dimensional bag parameter Lambda /sub B/=235 MeV and the quark-gluon coupling constant alpha =0.38 as defined at r/sub QQ/ approximately 0.2 fermi are determined from a good fit of the cc and bb spectra. The fit is in serious disagreement with the widely accepted MIT parameters. As an important test of their model, the authors calculate the rich spectrum of QQ glue states. In Upsilon particle spectroscopy they predict a narrow QQglue state with exotic quantum numbers J/sup PC/=1/sup -+/ below the BB threshold. Its experimental confirmation would be the first direct evidence for colored glue in the hadron spectrum. (3 refs).

  6. The infrared behavior of lattice QCD Green's functions. A numerical study of lattice QCD in Landau gauge

    International Nuclear Information System (INIS)

    Sternbeck, A.

    2006-01-01

    Within the framework of lattice QCD we investigate different aspects of QCD in Landau gauge using Monte Carlo simulations. In particular, we focus on the low momentum behavior of gluon and ghost propagators. The gauge group is SU(3). Different systematic effects on the gluon and ghost propagators are studied. We demonstrate the ghost dressing function to systematically depend on the choice of Gribov copies at low momentum, while the influence on the gluon dressing function is not resolvable. Also the eigenvalue distribution of the Faddeev-Popov operator is sensitive to Gribov copies. We show that the influence of dynamical Wilson fermions on the ghost propagator is negligible at the momenta available to us. On the contrary, fermions affect the gluon propagator at large and intermediate momenta. In addition, we analyze data for both propagators obtained on asymmetric lattices and compare these results with data obtained on symmetric lattices. We compare our data with results from studies of Dyson-Schwinger equations for the gluon and ghost propagators. We demonstrate that the infrared behavior of both propagators, as found in this thesis, is consistent with different criteria for confinement. However, the running coupling constant, given as a renormalization-group-invariant combination of the gluon and ghost dressing functions, does not expose a finite infrared fixed point. Rather the data are in favor of an infrared vanishing coupling constant. We also report on a first nonperturbative computation of the SU(3) ghost-gluon-vertex renormalization constant. We present results of an investigation of the spectral properties of the Faddeev-Popov operator. For this we have calculated the low-lying eigenvalues and eigenmodes of the Faddeev-Popov operator. (orig.)

  7. Infrared Behavior of Gluon and Ghost Propagators in Landau Gauge QCD

    International Nuclear Information System (INIS)

    von Smekal, L.; Hauck, A.; Alkofer, R.

    1997-01-01

    A truncation scheme for the Dyson-Schwinger equations of Euclidean QCD in Landau gauge is presented. It implements the Slavnov-Taylor identities for the three-gluon and ghost-gluon vertices, whereas irreducible four-gluon couplings as well as the gluon-ghost and ghost-ghost scattering kernels are neglected. The infrared behavior of gluon and ghost propagators is obtained analytically: The gluon propagator vanishes for small momenta, whereas the ghost propagator diverges strongly. The numerical solutions are compared with recent lattice results. The running coupling approaches a fixed point, α c ≅9.5 , in the infrared. copyright 1997 The American Physical Society

  8. Coulomb branches with complex singularities

    Science.gov (United States)

    Argyres, Philip C.; Martone, Mario

    2018-06-01

    We construct 4d superconformal field theories (SCFTs) whose Coulomb branches have singular complex structures. This implies, in particular, that their Coulomb branch coordinate rings are not freely generated. Our construction also gives examples of distinct SCFTs which have identical moduli space (Coulomb, Higgs, and mixed branch) geometries. These SCFTs thus provide an interesting arena in which to test the relationship between moduli space geometries and conformal field theory data. We construct these SCFTs by gauging certain discrete global symmetries of N = 4 superYang-Mills (sYM) theories. In the simplest cases, these discrete symmetries are outer automorphisms of the sYM gauge group, and so these theories have lagrangian descriptions as N = 4 sYM theories with disconnected gauge groups.

  9. Relevant energy scale of color confinement from lattice QCD

    International Nuclear Information System (INIS)

    Yamamoto, Arata; Suganuma, Hideo

    2009-01-01

    We propose a new lattice framework to extract the relevant gluonic energy scale of QCD phenomena which is based on a 'cut' on link variables in momentum space. This framework is expected to be broadly applicable to all lattice QCD calculations. Using this framework, we quantitatively determine the relevant energy scale of color confinement, through the analyses of the quark-antiquark potential and meson masses. The relevant energy scale of color confinement is found to be below 1.5 GeV in the Landau gauge. In fact, the string tension is almost unchanged even after cutting off the high-momentum gluon component above 1.5 GeV. When the relevant low-energy region is cut, the quark-antiquark potential is approximately reduced to a Coulomb-like potential, and each meson becomes a quasifree quark pair. As an analytical model calculation, we also investigate the dependence of the Richardson potential on the cut, and find the consistent behavior with the lattice result.

  10. Monte Carlo evidence for the gluon-chain model of QCD string formation

    International Nuclear Information System (INIS)

    Greensite, J.; San Francisco State Univ., CA

    1988-08-01

    The Monte Carlo method is used to calculate the overlaps string vertical stroken gluons>, where Ψ string [A] is the Yang-Mills wavefunctional due to a static quark-antiquark pair, and vertical stroken gluons > are orthogonal trial states containing n=0, 1, or 2 gluon operators multiplying the true ground state. The calculation is carried out for SU(2) lattice gauge theory in Coulomb gauge, in D=4 dimensions. It is found that the string state is dominated, at small qanti q separations, by the vacuum ('no-gluon') state, at larger separations by the 1-gluon state, and, at the largest separations attempted, the 2-gluon state begins to dominate. This behavior is in qualitative agreement with the gluon-chain model, which is a large-N colors motivated theory of QCD string formation. (orig.)

  11. Nonperturbative determination of the QCD potential at O(1/m)

    International Nuclear Information System (INIS)

    Koma, Y.; Koma, M.; Wittig, H.

    2006-07-01

    The relativistic correction to the QCD static inter-quark potential at O(1/m) is investigated nonperturbatively for the first time by using lattice Monte Carlo QCD simulations. The correction is found to be comparable with the Coulombic term of the static potential when applied to charmonium, and amounts to 26% of the Coulombic term for bottomonium. (Orig.)

  12. Coulomb string tension, asymptotic string tension, and the gluon chain

    OpenAIRE

    Greensite, Jeff; Szczepaniak, Adam P.

    2014-01-01

    We compute, via numerical simulations, the non-perturbative Coulomb potential of pure SU(3) gauge theory in Coulomb gauge. We find that that the Coulomb potential scales nicely in accordance with asymptotic freedom, that the Coulomb potential is linear in the infrared, and that the Coulomb string tension is about four times larger than the asymptotic string tension. We explain how it is possible that the asymptotic string tension can be lower than the Coulomb string tension by a factor of four.

  13. The Bayesian reconstruction of the in-medium heavy quark potential from lattice QCD and its stability

    Science.gov (United States)

    Burnier, Yannis; Kaczmarek, Olaf; Rothkopf, Alexander

    2016-01-01

    We report recent results of a non-perturbative determination of the static heavy-quark potential in quenched and dynamical lattice QCD at finite temperature. The real and imaginary part of this complex quantity are extracted from the spectral function of Wilson line correlators in Coulomb gauge. To obtain spectral information from Euclidean time numerical data, our study relies on a novel Bayesian prescription that differs from the Maximum Entropy Method. We perform simulations on quenched 323 × Nτ (β = 7.0, ξ = 3.5) lattices with Nτ = 24, …, 96, which cover 839MeV ≥ T ≥ 210MeV. To investigate the potential in a quark-gluon plasma with light u,d and s quarks we utilize Nf = 2 + 1 ASQTAD lattices with ml = ms/20 by the HotQCD collaboration, giving access to temperatures between 286MeV ≥ T ≥ 148MeV. The real part of the potential exhibits a clean transition from a linear, confining behavior in the hadronic phase to a Debye screened form above deconfinement. Interestingly its values lie close to the color singlet free energies in Coulomb gauge at all temperatures. We estimate the imaginary part on quenched lattices and find that it is of the same order of magnitude as in hard-thermal loop perturbation theory. From among all the systematic checks carried out in our study, we discuss explicitly the dependence of the result on the default model and the number of datapoints.

  14. Lattice calculations in gauge theory

    International Nuclear Information System (INIS)

    Rebbi, C.

    1985-01-01

    The lattice formulation of quantum gauge theories is discussed as a viable technique for quantitative studies of nonperturbative effects in QCD. Evidence is presented to ascertain that whole classes of lattice actions produce a universal continuum limit. Discrepancies between numerical results from Monto Carlo simulations for the pure gauge system and for the system with gauge and quark fields are discussed. Numerical calculations for QCD require very substantial computational resources. The use of powerful vector processors of special purpose machines, in extending the scope and magnitude or the calculations is considered, and one may reasonably expect that in the near future good quantitative predictions will be obtained for QCD

  15. The infrared behavior of lattice QCD Green's functions. A numerical study of lattice QCD in Landau gauge

    Energy Technology Data Exchange (ETDEWEB)

    Sternbeck, A.

    2006-07-18

    Within the framework of lattice QCD we investigate different aspects of QCD in Landau gauge using Monte Carlo simulations. In particular, we focus on the low momentum behavior of gluon and ghost propagators. The gauge group is SU(3). Different systematic effects on the gluon and ghost propagators are studied. We demonstrate the ghost dressing function to systematically depend on the choice of Gribov copies at low momentum, while the influence on the gluon dressing function is not resolvable. Also the eigenvalue distribution of the Faddeev-Popov operator is sensitive to Gribov copies. We show that the influence of dynamical Wilson fermions on the ghost propagator is negligible at the momenta available to us. On the contrary, fermions affect the gluon propagator at large and intermediate momenta. In addition, we analyze data for both propagators obtained on asymmetric lattices and compare these results with data obtained on symmetric lattices. We compare our data with results from studies of Dyson-Schwinger equations for the gluon and ghost propagators. We demonstrate that the infrared behavior of both propagators, as found in this thesis, is consistent with different criteria for confinement. However, the running coupling constant, given as a renormalization-group-invariant combination of the gluon and ghost dressing functions, does not expose a finite infrared fixed point. Rather the data are in favor of an infrared vanishing coupling constant. We also report on a first nonperturbative computation of the SU(3) ghost-gluon-vertex renormalization constant. We present results of an investigation of the spectral properties of the Faddeev-Popov operator. For this we have calculated the low-lying eigenvalues and eigenmodes of the Faddeev-Popov operator. (orig.)

  16. Gauge cooling for the singular-drift problem in the complex Langevin method — a test in Random Matrix Theory for finite density QCD

    Energy Technology Data Exchange (ETDEWEB)

    Nagata, Keitaro [KEK Theory Center, High Energy Accelerator Research Organization,1-1 Oho, Tsukuba 305-0801 (Japan); Nishimura, Jun [KEK Theory Center, High Energy Accelerator Research Organization,1-1 Oho, Tsukuba 305-0801 (Japan); Department of Particle and Nuclear Physics, School of High Energy Accelerator Science,Graduate University for Advanced Studies (SOKENDAI), 1-1 Oho, Tsukuba 305-0801 (Japan); Shimasaki, Shinji [KEK Theory Center, High Energy Accelerator Research Organization,1-1 Oho, Tsukuba 305-0801 (Japan); Research and Education Center for Natural Sciences, Keio University,Hiyoshi 4-1-1, Yokohama, Kanagawa 223-8521 (Japan)

    2016-07-14

    Recently, the complex Langevin method has been applied successfully to finite density QCD either in the deconfinement phase or in the heavy dense limit with the aid of a new technique called the gauge cooling. In the confinement phase with light quarks, however, convergence to wrong limits occurs due to the singularity in the drift term caused by small eigenvalues of the Dirac operator including the mass term. We propose that this singular-drift problem should also be overcome by the gauge cooling with different criteria for choosing the complexified gauge transformation. The idea is tested in chiral Random Matrix Theory for finite density QCD, where exact results are reproduced at zero temperature with light quarks. It is shown that the gauge cooling indeed changes drastically the eigenvalue distribution of the Dirac operator measured during the Langevin process. Despite its non-holomorphic nature, this eigenvalue distribution has a universal diverging behavior at the origin in the chiral limit due to a generalized Banks-Casher relation as we confirm explicitly.

  17. Construction of the dual Ginzburg-Landau theory from the lattice QCD

    International Nuclear Information System (INIS)

    Suganuma, H.; Amemiya, K.; Ichie, H.; Koma, Y.

    2002-01-01

    We roughly review the QCD physics and then introduce recent topics on the confinement physics. In the maximally abelian (MA) gauge, the low-energy QCD is abelianized owing to the effective off-diagonal gluon mass M off ≅ 1.2 GeV induced by the MA gauge fixing. We demonstrate the construction of the dual Ginzburg-Landau (DGL) theory from the low-energy QCD in the MA gauge in terms of the lattice QCD evidences on infrared abelian dominance and infrared monopole condensation. (author)

  18. Interquark potential with finite quark mass from lattice QCD.

    Science.gov (United States)

    Kawanai, Taichi; Sasaki, Shoichi

    2011-08-26

    We present an investigation of the interquark potential determined from the q ̄q Bethe-Salpeter (BS) amplitude for heavy quarkonia in lattice QCD. The q ̄q potential at finite quark mass m(q) can be calculated from the equal-time and Coulomb gauge BS amplitude through the effective Schrödinger equation. The definition of the potential itself requires information about a kinetic mass of the quark. We then propose a self-consistent determination of the quark kinetic mass on the same footing. To verify the proposed method, we perform quenched lattice QCD simulations with a relativistic heavy-quark action at a lattice cutoff of 1/a≈2.1  GeV in a range 1.0≤m(q)≤3.6 GeV. Our numerical results show that the q ̄q potential in the m(q)→∞ limit is fairly consistent with the conventional one obtained from Wilson loops. The quark-mass dependence of the q ̄q potential and the spin-spin potential are also examined. © 2011 American Physical Society

  19. Academic Training Lectures - QCD for Postgraduates

    CERN Multimedia

    Maureen Prola-Tessaur

    2010-01-01

    by Giulia Zanderighi (University of Oxford) Monday 12 to Friday 16 April 2010 From 11:00 to 12:00 - Main Auditorium, Bldg. 500-1-001 Monday 12 - Modern QCD - Lecture 1 Starting from the QCD Lagrangian we will revisit some basic QCD concepts and derive fundamental properties like gauge invariance and isospin symmetry and will discuss the Feynman rules of the theory. We will then focus on the gauge group of QCD and derive the Casimirs CF and CA and some useful color identities. Tuesday 13 - Modern QCD - Lecture 2 We will start discussing the matter content of the theory and revisit the experimental measurements that led to the discovery of quarks. We will then consider a classic QCD observable, the R-ratio, and use it to illustrate the appearance of UV divergences and the need to renormalize the coupling constant of QCD. We will then discuss asymptotic freedom and confinement. Finally, we will examine a case where soft and collinear infrared divergences appear, will discuss the soft approximation in QCD ...

  20. Gauge theories

    International Nuclear Information System (INIS)

    Lee, B.W.

    1976-01-01

    Some introductory remarks to Yang-Mills fields are given and the problem of the Coulomb gauge is considered. The perturbation expansion for quantized gauge theories is discussed and a survey of renormalization schemes is made. The role of Ward-Takahashi identities in gauge theories is discussed. The author then discusses the renormalization of pure gauge theories and theories with spontaneously broken symmetry. (B.R.H.)

  1. Observation of a Coulomb flux tube

    Science.gov (United States)

    Greensite, Jeff; Chung, Kristian

    2018-03-01

    In Coulomb gauge there is a longitudinal color electric field associated with a static quark-antiquark pair. We have measured the spatial distribution of this field, and find that it falls off exponentially with transverse distance from a line joining the two quarks. In other words there is a Coulomb flux tube, with a width that is somewhat smaller than that of the minimal energy flux tube associated with the asymptotic string tension. A confinement criterion for gauge theories with matter fields is also proposed.

  2. Light-front QCD. II. Two-component theory

    International Nuclear Information System (INIS)

    Zhang, W.; Harindranath, A.

    1993-01-01

    The light-front gauge A a + =0 is known to be a convenient gauge in practical QCD calculations for short-distance behavior, but there are persistent concerns about its use because of its ''singular'' nature. The study of nonperturbative field theory quantizing on a light-front plane for hadronic bound states requires one to gain a priori systematic control of such gauge singularities. In the second paper of this series we study the two-component old-fashioned perturbation theory and various severe infrared divergences occurring in old-fashioned light-front Hamiltonian calculations for QCD. We also analyze the ultraviolet divergences associated with a large transverse momentum and examine three currently used regulators: an explicit transverse cutoff, transverse dimensional regularization, and a global cutoff. We discuss possible difficulties caused by the light-front gauge singularity in the applications of light-front QCD to both old-fashioned perturbative calculations for short-distance physics and upcoming nonperturbative investigations for hadronic bound states

  3. Overview of lattice gauge theory at the CSSM

    International Nuclear Information System (INIS)

    Williams, A.G.

    2002-01-01

    Full text: I present an overview of the lattice gauge theory effort at the Special Research Centre for the Subatomic Structure of Matter (CSSM). The CSSM specializes in research into the strong interactions and into quantum chromodynamics (QCD), which is the fundamental quantum gauge field theory of the strong interactions. The primary mission of the CSSM is to attempt to solve QCD and hence test the implications of the theory against experimental evidence. The difficulty lies in the fact that the QCD is a highly nonlinear, strongly coupled theory. The only known first-principles means to solve it is to approximate space-time by a four-dimensional 'grid' or 'lattice' and to simulate this 'lattice QCD' on massively parallel supercomputers. A discussion of the Orion supercomputer of the National Computing Facility for Lattice Gauge Theory (NFCLGT) and the latest QCD predictions obtained from Orion by CSSM researchers will be presented

  4. Perturbative QCD (1/3)

    CERN Multimedia

    CERN. Geneva

    2013-01-01

    Perturbative QCD is the general theoretical framework for describing hard scattering processes yielding multiparticle production at hadron colliders. In these lectures, we shall introduce fundamental features of perturbative QCD and describe its application to several high energy collider processes, including jet production in electron-positron annihilation, deep inelastic scattering, Higgs boson and gauge boson production at the LHC.

  5. Coulomb interference and bending slope in hadron-hadron scattering

    International Nuclear Information System (INIS)

    Pereira, Flavio I.; Ferreira, Erasmo

    1994-01-01

    With the purpose of testing the results of QCD calculations on the structure of the forward elastic scattering cross-section, we analyse the coulombic-nuclear interference occurring at small values of the momentum transfer. We emphasize the influence of the hadronic structures on the determination of the Coulomb phase and consequently on the t-dependence of the strong interaction slope parameter. (author)

  6. An introduction to gauge theories

    CERN Document Server

    Cabibbo, Nicola; Benhar, Omar

    2017-01-01

    Written by three of the world's leading experts on particle physics and the standard model, including an award-winning former director general of CERN, this book provides a completely up-to-date account of gauge theories. Starting from Feynman’s path integrals, Feynman rules are derived, gauge fixing and Faddeev-Popov ghosts are discussed, and renormalization group equations are derived. Several important applications to quantum electrodynamics and quantum chromodynamics (QCD) are discussed, including the one-loop derivation of asymptotic freedom for QCD.

  7. Color-magnetic permeability of QCD vacuum

    Energy Technology Data Exchange (ETDEWEB)

    Saito, T [Kyoto Prefectural Univ. of Medicine (Japan); Shigemoto, K

    1980-03-01

    In the very strong background gauge field the QCD true vacuum has been shown to have lower energy than the ''perturbative vacuum.'' The color-magnetic permeability of the QCD true vacuum is then calculated to be 1/2 within the quark-one-loop approximation.

  8. National Computational Infrastructure for Lattice Gauge Theory

    Energy Technology Data Exchange (ETDEWEB)

    Brower, Richard C.

    2014-04-15

    SciDAC-2 Project The Secret Life of Quarks: National Computational Infrastructure for Lattice Gauge Theory, from March 15, 2011 through March 14, 2012. The objective of this project is to construct the software needed to study quantum chromodynamics (QCD), the theory of the strong interactions of sub-atomic physics, and other strongly coupled gauge field theories anticipated to be of importance in the energy regime made accessible by the Large Hadron Collider (LHC). It builds upon the successful efforts of the SciDAC-1 project National Computational Infrastructure for Lattice Gauge Theory, in which a QCD Applications Programming Interface (QCD API) was developed that enables lattice gauge theorists to make effective use of a wide variety of massively parallel computers. This project serves the entire USQCD Collaboration, which consists of nearly all the high energy and nuclear physicists in the United States engaged in the numerical study of QCD and related strongly interacting quantum field theories. All software developed in it is publicly available, and can be downloaded from a link on the USQCD Collaboration web site, or directly from the github repositories with entrance linke http://usqcd-software.github.io

  9. Coulomb energy, vortices, and confinement

    International Nuclear Information System (INIS)

    Greensite, Jeff; Olejnik, Stefan

    2003-01-01

    We estimate the Coulomb energy of static quarks from a Monte Carlo calculation of the correlator of timelike link variables in the Coulomb gauge. We find, in agreement with Cucchieri and Zwanziger, that this energy grows linearly with distance at large quark separations. The corresponding string tension, however, is several times greater than the accepted asymptotic string tension, indicating that a state containing only static sources, with no constituent gluons, is not the lowest energy flux tube state. The Coulomb energy is also measured on thermalized lattices with center vortices removed by the de Forcrand-D'Elia procedure. We find that when vortices are removed, the Coulomb string tension vanishes

  10. QCD as a Theory of Hadrons

    Science.gov (United States)

    Narison, Stephan

    2007-07-01

    About Stephan Narison; Outline of the book; Preface; Acknowledgements; Part I. General Introduction: 1. A short flash on particle physics; 2. The pre-QCD era; 3. The QCD story; 4. Field theory ingredients; Part II. QCD Gauge Theory: 5. Lagrangian and gauge invariance; 6. Quantization using path integral; 7. QCD and its global invariance; Part III. MS scheme for QCD and QED: Introduction; 8. Dimensional regularization; 9. The MS renormalization scheme; 10. Renormalization of operators using the background field method; 11. The renormalization group; 12. Other renormalization schemes; 13. MS scheme for QED; 14. High-precision low-energy QED tests; Part IV. Deep Inelastic Scattering at Hadron Colliders: 15. OPE for deep inelastic scattering; 16. Unpolarized lepton-hadron scattering; 17. The Altarelli-Parisi equation; 18. More on unpolarized deep inelastic scatterings; 19. Polarized deep-inelastic processes; 20. Drell-Yan process; 21. One 'prompt photon' inclusive production; Part V. Hard Processes in e+e- Collisions: Introduction; 22. One hadron inclusive production; 23. gg scatterings and the 'spin' of the photon; 24. QCD jets; 25. Total inclusive hadron productions; Part VI. Summary of QCD Tests and as Measurements; Part VII. Power Corrections in QCD: 26. Introduction; 27. The SVZ expansion; 28. Technologies for evaluating Wilson coefficients; 29. Renormalons; 30. Beyond the SVZ expansion; Part VIII. QCD Two-Point Functions: 31. References guide to original works; 32. (Pseudo)scalar correlators; 33. (Axial-)vector two-point functions; 34. Tensor-quark correlator; 35. Baryonic correlators; 36. Four-quark correlators; 37. Gluonia correlators; 38. Hybrid correlators; 39. Correlators in x-space; Part IX. QCD Non-Perturbative Methods: 40. Introduction; 41. Lattice gauge theory; 42. Chiral perturbation theory; 43. Models of the QCD effective action; 44. Heavy quark effective theory; 45. Potential approaches to quarkonia; 46. On monopole and confinement; Part X. QCD

  11. Scattering amplitudes in four- and six-dimensional gauge theories

    International Nuclear Information System (INIS)

    Schuster, Theodor

    2014-01-01

    We study scattering amplitudes in quantum chromodynamics (QCD), N=4 super Yang-Mills (SYM) theory and the six-dimensional N=(1,1) SYM theory, focusing on the symmetries of and relations between the tree-level scattering amplitudes in these three gauge theories. We derive the tree level and one-loop color decomposition of an arbitrary QCD amplitude into primitive amplitudes. Furthermore, we derive identities spanning the null space among the primitive amplitudes. We prove that every color ordered tree amplitude of massless QCD can be obtained from gluon-gluino amplitudes of N=4 SYM theory. Furthermore, we derive analytical formulae for all gluon-gluino amplitudes relevant for QCD. We compare the numerical efficiency and accuracy of evaluating these closed analytic formulae for color ordered QCD tree amplitudes to a numerically efficient implementation of the Berends-Giele recursion. We derive the symmetries of massive tree amplitudes on the coulomb branch of N=4 SYM theory, which in turn can be obtained from N=(1,1) SYM theory by dimensional reduction. Furthermore, we investigate the tree amplitudes of N=(1, 1) SYM theory and explain how analytical formulae can be obtained from a numerical implementation of the supersymmetric BCFW recursion relation and investigate a potential uplift of the massless tree amplitudes of N=4 SYM theory. Finally we study an alternative to dimensional regularization of N=4 SYM theory. The infrared divergences are regulated by masses obtained from a Higgs mechanism. The corresponding string theory set-up suggests that the amplitudes have an exact dual conformal symmetry. We confirm this expectation and illustrate the calculational advantages of the massive regulator by explicit calculations.

  12. Chern-Simons induced spin factors in noncovariant gauges

    International Nuclear Information System (INIS)

    Tanaka, I.

    1993-01-01

    We study Chern-Simons induced spin factors in noncovariant metric-independent gauges, such as the axial gauge and the Coulomb gauge. These spin factors are defined without loop splitting. We find that they are equal to integers and have particular geometrical meanings. In the axial gauge, this integer is the writhe number of a link diagram defined by the projection of a loop to the time direction. In the Coulomb gauge, it is suggested that this integer is also the writhe number of a link diagram, defined by the projection of a loop to a spatial plane

  13. Behavior of the S parameter in the crossover region between walking and QCD-like regimes of an SU(N) gauge theory

    International Nuclear Information System (INIS)

    Kurachi, Masafumi; Shrock, Robert

    2006-01-01

    We consider a vectorial, confining SU(N) gauge theory with a variable number, N f , of massless fermions transforming according to the fundamental representation. Using the Schwinger-Dyson and Bethe-Salpeter equations, we calculate the S parameter in terms of the current-current correlation functions. We focus on values of N f such that the theory is in the crossover region between the regimes of walking behavior and QCD-like (nonwalking) behavior. Our calculations indicate that the contribution to S from a given fermion decreases as one moves from the QCD-like to the walking regimes. The implications of this result for technicolor theories are discussed

  14. Multi-Quarks and Two-Baryon Interaction in Lattice QCD

    International Nuclear Information System (INIS)

    Okiharu, F.; Suganuma, H.; Takahashi, T. T.; Doi, T.

    2006-01-01

    We study multi-quark (3Q,4Q,5Q) systems in lattice QCD. We perform the detailed studies of multi-quark potentials in lattice QCD to clarify the inter-quark interaction in multi-quark systems. We find that all the multi-quark potentials are well described by the OGE Coulomb plus multi-Y-type linear potential, i.e., the multi-Y Ansatz. For multi-quark systems, we observe lattice QCD evidences of 'flip-flop', i.e., flux-tube recombination. These lattice QCD studies give an important bridge between elementary particle physics and nuclear physics

  15. Statistical mechanics view of quantum chromodynamics: Lattice gauge theory

    International Nuclear Information System (INIS)

    Kogut, J.B.

    1984-01-01

    Recent developments in lattice gauge theory are discussed from a statistial mechanics viewpoint. The basic physics problems of quantum chromodynamics (QCD) are reviewed for an audience of critical phenomena theorists. The idea of local gauge symmetry and color, the connection between statistical mechanics and field theory, asymptotic freedom and the continuum limit of lattice gauge theories, and the order parameters (confinement and chiral symmetry) of QCD are reviewed. Then recent developments in the field are discussed. These include the proof of confinement in the lattice theory, numerical evidence for confinement in the continuum limit of lattice gauge theory, and perturbative improvement programs for lattice actions. Next, we turn to the new challenges facing the subject. These include the need for a better understanding of the lattice Dirac equation and recent progress in the development of numerical methods for fermions (the pseudofermion stochastic algorithm and the microcanonical, molecular dynamics equation of motion approach). Finally, some of the applications of lattice gauge theory to QCD spectrum calculations and the thermodynamics of QCD will be discussed and a few remarks concerning future directions of the field will be made

  16. Gluon and ghost correlation functions of 2-color QCD at finite density

    Science.gov (United States)

    Hajizadeh, Ouraman; Boz, Tamer; Maas, Axel; Skullerud, Jon-Ivar

    2018-03-01

    2-color QCD, i. e. QCD with the gauge group SU(2), is the simplest non-Abelian gauge theory without sign problem at finite quark density. Therefore its study on the lattice is a benchmark for other non-perturbative approaches at finite density. To provide such benchmarks we determine the minimal-Landau-gauge 2-point and 3-gluon correlation functions of the gauge sector and the running gauge coupling at finite density. We observe no significant effects, except for some low-momentum screening of the gluons at and above the supposed high-density phase transition.

  17. The chiral bosonization in non-Abelian gauge theories

    International Nuclear Information System (INIS)

    Andrianov, A.A.; Novozhilov, Y.

    1985-01-01

    The chiral bosonization in non-Abelian gauge theories is described starting directly from the QCD functional. For a given mass scale Λ, the QCD may be equivalently represented by colour chiral fields, gauge fields and high energy fermions. The effective action for colour chiral fields may admit the existence of a colour Skyrmion-boson with the baryon number 2/3. (author)

  18. Linear energy divergences in Coulomb gauge QCD

    OpenAIRE

    Andrasi, A.

    2011-01-01

    The structure of linear energy divergences is analysed on the example of one graph to 3-loop order. Such dangerous divergences do cancel when all graphs are added, but next to leading divergences do not cancel out.

  19. Nonperturbation aspects of QCD. Monte Carlo and optimization

    International Nuclear Information System (INIS)

    Brezin, E.; Morel, A.; Marinari, E.; Couchot, F.; Narison, S.; Richard, J.M.; Blaizot, J.P.; Souillard, B.

    1986-01-01

    Phase transitions; lattice QCD; numerical simulation of lattice gauge theories; experimental research on gluonic mesons; QCD-duality sum rules; the bag model, potentials, and hadron spectra; and efficient Lagrangian functions and the Skyrme model are introduced [fr

  20. Lattice gauge theory for QCD

    International Nuclear Information System (INIS)

    DeGrand, T.

    1997-01-01

    These lectures provide an introduction to lattice methods for nonperturbative studies of Quantum Chromodynamics. Lecture 1: Basic techniques for QCD and results for hadron spectroscopy using the simplest discretizations; lecture 2: Improved actions--what they are and how well they work; lecture 3: SLAC physics from the lattice-structure functions, the mass of the glueball, heavy quarks and α s (M z ), and B-anti B mixing. 67 refs., 36 figs

  1. QCD in gauge-boson production at the LHC

    CERN Document Server

    Schott, Matthias; The ATLAS collaboration

    2018-01-01

    Measurements of the Drell-Yan production of W and Z/gamma* bosons at the LHC provide a benchmark of our understanding of perturbative QCD and probe the proton structure in a unique way. The ATLAS and CMS collaborations have performed several high precision measurements at different center-of-mass energies, ranging from single to triple differential cross sections. These measurements are the key in improving physics modelling uncertainties of electroweak precision measurements at the LHC. Moreover, perturbative QCD can be tested further in a multi-scale environment, when studying the production of jets in association with single and di-bosons final states. In this talk, we review the latest measurements, discuss the compatibility between the experiments and compare the results to the state-of-the-art QCD calculations and Monte Carlo simulations, as well their potential impact on improving our understanding PDFs.

  2. SO(2N) and SU(N) gauge theories

    OpenAIRE

    Lau, Richard; Teper, Michael

    2013-01-01

    We present our preliminary results of SO(2N) gauge theories, approaching the large-N limit. SO(2N) theories may help us to understand QCD at finite chemical potential since there is an orbifold equivalence between SO(2N) and SU(N) gauge theories at large-N and SO(2N) theories do not have the sign problem present in QCD. We consider the string tensions, mass spectra, and deconfinement temperatures in the SO(2N) pure gauge theories in 2+1 dimensions, comparing them to their corresponding SU(N) ...

  3. The Coulomb Branch of 3d N= 4 Theories

    Science.gov (United States)

    Bullimore, Mathew; Dimofte, Tudor; Gaiotto, Davide

    2017-09-01

    We propose a construction for the quantum-corrected Coulomb branch of a general 3d gauge theory with N=4 supersymmetry, in terms of local coordinates associated with an abelianized theory. In a fixed complex structure, the holomorphic functions on the Coulomb branch are given by expectation values of chiral monopole operators. We construct the chiral ring of such operators, using equivariant integration over BPS moduli spaces. We also quantize the chiral ring, which corresponds to placing the 3d theory in a 2d Omega background. Then, by unifying all complex structures in a twistor space, we encode the full hyperkähler metric on the Coulomb branch. We verify our proposals in a multitude of examples, including SQCD and linear quiver gauge theories, whose Coulomb branches have alternative descriptions as solutions to Bogomolnyi and/or Nahm equations.

  4. Lattice gauge theory for QCD

    Energy Technology Data Exchange (ETDEWEB)

    DeGrand, T. [Univ. of Colorado, Boulder, CO (United States). Dept. of Physics

    1997-06-01

    These lectures provide an introduction to lattice methods for nonperturbative studies of Quantum Chromodynamics. Lecture 1: Basic techniques for QCD and results for hadron spectroscopy using the simplest discretizations; lecture 2: Improved actions--what they are and how well they work; lecture 3: SLAC physics from the lattice-structure functions, the mass of the glueball, heavy quarks and {alpha}{sub s} (M{sub z}), and B-{anti B} mixing. 67 refs., 36 figs.

  5. QCD propagators and vertices from lattice QCD (in memory of Michael Müller-Preußker

    Directory of Open Access Journals (Sweden)

    Sternbeck André

    2017-01-01

    Full Text Available We review lattice calculations of the elementary Greens functions of QCD with a special emphasis on the Landau gauge. These lattice results have been of interest to continuum approaches to QCD over the past 20 years. They are used as reference for Dyson-Schwinger- and functional renormalization group equation calculations as well as for hadronic bound state equations. The lattice provides low-energy data for propagators and three-point vertices in Landau gauge at zero and finite temperature even including dynamical fermions. We summarize Michael Müller-Preußker’s important contributions to this field and put them into the perspective of his other research interests.

  6. QCD at finite temperature

    International Nuclear Information System (INIS)

    Kikkawa, Keiji

    1983-01-01

    The varidity of the perturbation method in the high temperature QCD is discussed. The skeleton expansion method takes account of plasmon effects and eliminates the electric infrared singularity but not the magnetic one. A possibility of eliminating the latter, which was recently proposed, is examined by a gauge invariant skeleton expansion. The magnetic singularity is unable to be eliminated by the perturbation method. This implies that some non-perturbative approaches must be incorporated in the high temperature QCD. (author)

  7. Gauge field theory

    International Nuclear Information System (INIS)

    Aref'eva, I.Ya.; Slavnov, A.A.

    1981-01-01

    This lecture is devoted to the discussion of gauge field theory permitting from the single point of view to describe all the interactions of elementary particles. The authors used electrodynamics and the Einstein theory of gravity to search for a renormgroup fixing a form of Lagrangian. It is shown that the gauge invariance added with the requirement of the minimum number of arbitraries in Lagrangian fixes unambigously the form of the electromagnetic interaction. The generalization of this construction for more complicate charge spaces results in the Yang-Mills theory. The interaction form in this theory is fixed with the relativity principle in the charge space. A quantum scheme of the Yang-Mills fields through the explicit separation of true dynamic variables is suggested. A comfortable relativistically invariant diagram technique for the calculation of a producing potential for the Green functions is described. The Ward generalized identities have been obtained and a procedure of the elimination of ultraviolet and infrared divergencies has been accomplished. Within the framework of QCD (quantum-chromodynamic) the phenomenon of the asymptotic freedom being the most successful prediction of the gauge theory of strong interactions was described. Working methods with QCD outside the framework of the perturbation theory have been described from a coupling constant. QCD is represented as a single theory possessing both the asymptotical freedom and the freedom retaining quarks [ru

  8. Gluon and ghost propagator studies in lattice QCD at finite temperature

    International Nuclear Information System (INIS)

    Aouane, Rafik

    2013-01-01

    Gluon and ghost propagators in quantum chromodynamics (QCD) computed in the infrared momentum region play an important role to understand quark and gluon confinement. They are the subject of intensive research thanks to non-perturbative methods based on Dyson-Schwinger (DS) and functional renormalization group (FRG) equations. Moreover, their temperature behavior might also help to explore the chiral and deconfinement phase transition or crossover within QCD at non-zero temperature. Our prime tool is the lattice discretized QCD (LQCD) providing a unique ab-initio non-perturbative approach to deal with the computation of various observables of the hadronic world. We investigate the temperature dependence of Landau gauge gluon and ghost propagators in pure gluodynamics and in full QCD. Regarding the gluon propagator, we compute its longitudinal D L as well its transversal D T components. The aim is to provide a data set in terms of fitting formulae which can be used as input for DS (or FRG) equations. We deal with full (N f =2) LQCD with the twisted mass fermion discretization. We employ gauge field configurations provided by the tmfT collaboration for temperatures in the crossover region and for three fixed pion mass values in the range [300,500] MeV. Finally, within SU(3) pure gauge theory (at T=0) we compute the Landau gauge gluon propagator according to different gauge fixing criteria. Our goal is to understand the influence of gauge copies with minimal (non-trivial) eigenvalues of the Faddeev-Popov operator.

  9. Tensor gauge condition and tensor field decomposition

    Science.gov (United States)

    Zhu, Ben-Chao; Chen, Xiang-Song

    2015-10-01

    We discuss various proposals of separating a tensor field into pure-gauge and gauge-invariant components. Such tensor field decomposition is intimately related to the effort of identifying the real gravitational degrees of freedom out of the metric tensor in Einstein’s general relativity. We show that as for a vector field, the tensor field decomposition has exact correspondence to and can be derived from the gauge-fixing approach. The complication for the tensor field, however, is that there are infinitely many complete gauge conditions in contrast to the uniqueness of Coulomb gauge for a vector field. The cause of such complication, as we reveal, is the emergence of a peculiar gauge-invariant pure-gauge construction for any gauge field of spin ≥ 2. We make an extensive exploration of the complete tensor gauge conditions and their corresponding tensor field decompositions, regarding mathematical structures, equations of motion for the fields and nonlinear properties. Apparently, no single choice is superior in all aspects, due to an awkward fact that no gauge-fixing can reduce a tensor field to be purely dynamical (i.e. transverse and traceless), as can the Coulomb gauge in a vector case.

  10. Kohn-Luttinger effect in gauge theories

    International Nuclear Information System (INIS)

    Schaefer, T.

    2006-01-01

    Kohn and Luttinger showed that a many body system of fermions interacting via short range forces becomes superfluid even if the interaction is repulsive in all partial waves. In gauge theories such as QCD the interaction between fermions is long range and the assumptions of Kohn and Luttinger are not satisfied. We show that in a U(1) gauge theory the Kohn-Luttinger phenomenon does not take place. In QCD attractive channels always exist, but there are cases in which the primary pairing channel leaves some fermions ungapped. As an example we consider the unpaired fermion in the 2SC phase of QCD with two flavors. We show that it acquires a very small gap via a mechanism analogous to the Kohn-Luttinger effect. The gap is too small to be phenomenologically relevant

  11. Roles of the color antisymmetric ghost propagator in the Infrared QCD

    International Nuclear Information System (INIS)

    Furui, S.

    2009-01-01

    The results of Coulomb gauge and Landau gauge lattice QCD simulation do not agree completely with continuum theory. There are indications that the ghost propagator in the infrared region has strong fluctuation whose modulus is compatible with that of the color diagonal ghost propagator. After presenting lattice simulation of configurations produced with Kogut-Susskind fermion (MILC collaboration) and those with domain wall fermion (RBC/UKQCD collaboration), I investigate in triple gluon vertex and the ghost-gluon-ghost vertex how the square of the color antisymmetric ghost contributes. Then the effect of the vertex correction to the gluon propagator and the ghost propagator is investigated. Recent Dyson-Schwinger equation analysis suggests the ghost dressing function G(0) = finite and no infrared enhancement or a G = 0. But the ghost propagator renormalized by the loop containing a product of color antisymmetric ghost is expected to behave as [cc] r = - (G(q 2 ))/(q 2 ) with G(q 2 ) ∝ q -2aG with a G = 0.5, if the fixed point scenario is valid. I interpret the a G = 0 solution should contain a vertex correction. The infrared exponent of our lattice Landau gauge gluon propagator of the RBC/UKQCD is a D = - 0.5 and that of MILC is about - 0.7. A possible interpretation of the origin of the fluctuation is given. (author)

  12. Improved methods for the study of hadronic physics from lattice QCD

    International Nuclear Information System (INIS)

    Orginos, Kostas; Richards, David

    2015-01-01

    The solution of quantum chromodynamics (QCD) on a lattice provides a first-principles method for understanding QCD in the low-energy regime, and is thus an essential tool for nuclear physics. The generation of gauge configurations, the starting point for lattice calculations, requires the most powerful leadership-class computers available. However, to fully exploit such leadership-class computing requires increasingly sophisticated methods for obtaining physics observables from the underlying gauge ensembles. In this paper, we describe a variety of recent methods that have been used to advance our understanding of the spectrum and structure of hadrons through lattice QCD. (paper)

  13. Improved methods for the study of hadronic physics from lattice QCD

    Energy Technology Data Exchange (ETDEWEB)

    Orginos, Kostas [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); College of William and Mary, Williamsburg, VA (United States); Richards, David [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)

    2015-02-05

    The solution of QCD on a lattice provides a first-principles method for understanding QCD in the low-energy regime, and is thus an essential tool for nuclear physics. The generation of gauge configurations, the starting point for lattice calculations, requires the most powerful leadership-class computers available. However, to fully exploit such leadership-class computing requires increasingly sophisticated methods for obtaining physics observables from the underlying gauge ensembles. In this study, we describe a variety of recent methods that have been used to advance our understanding of the spectrum and structure of hadrons through lattice QCD.

  14. Topics in quantum chromodynamics: two loop Feynman gauge calculation of the meson nonsinglet evolution potential and fourier acceleration of the calculation of the fermion propagator in lattice QCD

    International Nuclear Information System (INIS)

    Katz, G.R.

    1986-01-01

    Part I of this thesis is a perturbative QCD calculation to two loops of the meson nonsinglet evolution potential in the Feynman gauge. The evolution potential describes the momentum dependence of the distribution amplitude. This amplitude is needed for the calculation to beyond leading order of exclusive amplitudes and form factors. Techniques are presented that greatly simplify the calculation. The results agree with an independent light-cone gauge calculation and disagree with predictions made using conformal symmetry. In Part II the author presents a Fourier acceleration method that is effective in accelerating the computation of the fermion propagator in lattice QCD. The conventional computation suffers from critical slowing down: the long distance structure converges much slower than the short distance structure. by evaluating the fermion propagator in momentum space using fast Fourier transforms, it is possible to make different length scales converge at a more equal rate. From numerical experiments made on a 8 4 lattice, the author obtained savings of a factor of 3 to 4 by using Fourier acceleration. He also discusses the important of gauge fixing when using Fourier acceleration

  15. Static QCD potential at rQCD-1: Perturbative expansion and operator-product expansion

    International Nuclear Information System (INIS)

    Sumino, Y.

    2007-01-01

    We analyze the static QCD potential V QCD (r) in the distance region 0.1 fm QCD (r) analytically. Higher-order terms are estimated by large-β 0 approximation or by renormalization group, and the renormalization scale is varied around the minimal-sensitivity scale. A 'Coulomb'+linear potential can be identified with the scale-independent and renormalon-free part of the prediction and can be separated from the renormalon-dominating part. (II) In the frame of OPE, we define two types of renormalization schemes for the leading Wilson coefficient. One scheme belongs to the class of conventional factorization schemes. The other scheme belongs to a new class, which is independent of the factorization scale, derived from a generalization of the Coulomb+linear potential of (I). The Wilson coefficient is free from IR renormalons and IR divergences in both schemes. We study properties of the Wilson coefficient and of the corresponding nonperturbative contribution δE US (r) in each scheme. (III) We compare numerically perturbative predictions of the Wilson coefficient and lattice computations of V QCD (r) when n l =0. We confirm either correctness or consistency (within uncertainties) of the theoretical predictions made in (II). Then we perform fits to simultaneously determine δE US (r) and r 0 Λ MS 3-loop (relation between lattice scale and Λ MS ). As for the former quantity, we improve bounds as compared to the previous determination; as for the latter quantity, our analysis provides a new method for its determination. We find that (a) δE US (r)=0 is disfavored, and (b) r 0 Λ MS 3-loop =0.574±0.042. We elucidate the mechanism for the sensitivities and examine sources of errors in detail

  16. Gauge invariant sub-structures of tree-level double-emission exact QCD spin amplitudes

    CERN Document Server

    Van Hameren, A

    2009-01-01

    In this note we discuss possible separations of exact, massive, tree-level spin amplitudes into gauge invariant parts. We concentrate our attention on processes involving two quarks entering a color- neutral current and, thanks to the QCD interactions, two extra external gluons. We will search for forms compatible with parton shower languages, without applying approximations or restrictions on phase space regions. Special emphasis will be put on the isolation of parts necessary for the construction of evolution kernels for individual splittings and to some degree for the running coupling constant as well. Our aim is to better understand the environment necessary to optimally match hard matrix elements with partons shower algorithms. To avoid complications and ambiguities related to regularization schemes, we ignore, at this point, virtual corrections. Our representation is quite universal: any color-neutral current can be used, in particular our approach is not restricted to vector currents only.

  17. Unusual identities for QCD at tree-level

    International Nuclear Information System (INIS)

    Bjerrum-Bohr, N E J; Damgaard, Poul H; Soendergaard, Thomas; Feng Bo

    2011-01-01

    We discuss a set of recently discovered quadratic relations between gauge theory amplitudes. Such relations give additional structural simplifications for amplitudes in QCD. Remarkably, their origin lie in an analogous set of relations that involve also gravitons. When certain gluon helicities are flipped we obtain relations that do not involve gravitons, but which refer only to QCD.

  18. Tests of hard and soft QCD with $e^{+}e^{-}$ Annihilation Data

    CERN Document Server

    Kluth, S

    2002-01-01

    Experimental tests of QCD predictions for event shape distributions combining contributions from hard and soft processes are discussed. The hard processes are predicted by perturbative QCD calculations. The soft processes cannot be calculated directly using perturbative QCD, they are treated by a power correction model based on the analysis of infrared renormalons. Furthermore, an analysis of the gauge structure of QCD is presented using fits of the colour factors within the same combined QCD predictions.

  19. Gluon and ghost propagator studies in lattice QCD at finite temperature

    Energy Technology Data Exchange (ETDEWEB)

    Aouane, Rafik

    2013-04-29

    Gluon and ghost propagators in quantum chromodynamics (QCD) computed in the infrared momentum region play an important role to understand quark and gluon confinement. They are the subject of intensive research thanks to non-perturbative methods based on Dyson-Schwinger (DS) and functional renormalization group (FRG) equations. Moreover, their temperature behavior might also help to explore the chiral and deconfinement phase transition or crossover within QCD at non-zero temperature. Our prime tool is the lattice discretized QCD (LQCD) providing a unique ab-initio non-perturbative approach to deal with the computation of various observables of the hadronic world. We investigate the temperature dependence of Landau gauge gluon and ghost propagators in pure gluodynamics and in full QCD. Regarding the gluon propagator, we compute its longitudinal D{sub L} as well its transversal D{sub T} components. The aim is to provide a data set in terms of fitting formulae which can be used as input for DS (or FRG) equations. We deal with full (N{sub f}=2) LQCD with the twisted mass fermion discretization. We employ gauge field configurations provided by the tmfT collaboration for temperatures in the crossover region and for three fixed pion mass values in the range [300,500] MeV. Finally, within SU(3) pure gauge theory (at T=0) we compute the Landau gauge gluon propagator according to different gauge fixing criteria. Our goal is to understand the influence of gauge copies with minimal (non-trivial) eigenvalues of the Faddeev-Popov operator.

  20. Equivalence of the AdS-metric and the QCD running coupling

    Science.gov (United States)

    Pirner, H. J.; Galow, B.

    2009-08-01

    We use the functional form of the QCD running coupling to modify the conformal metric in AdS/CFT mapping the fifth-dimensional z-coordinate to the energy scale in the four-dimensional QCD. The resulting type-0 string theory in five dimensions is solved with the Nambu-Goto action giving good agreement with the Coulombic and confinement QQbar potential.

  1. Gauge-fixing parameter dependence of two-point gauge-variant correlation functions

    International Nuclear Information System (INIS)

    Zhai, C.

    1996-01-01

    The gauge-fixing parameter ξ dependence of two-point gauge-variant correlation functions is studied for QED and QCD. We show that, in three Euclidean dimensions, or for four-dimensional thermal gauge theories, the usual procedure of getting a general covariant gauge-fixing term by averaging over a class of covariant gauge-fixing conditions leads to a nontrivial gauge-fixing parameter dependence in gauge-variant two-point correlation functions (e.g., fermion propagators). This nontrivial gauge-fixing parameter dependence modifies the large-distance behavior of the two-point correlation functions by introducing additional exponentially decaying factors. These factors are the origin of the gauge dependence encountered in some perturbative evaluations of the damping rates and the static chromoelectric screening length in a general covariant gauge. To avoid this modification of the long-distance behavior introduced by performing the average over a class of covariant gauge-fixing conditions, one can either choose a vanishing gauge-fixing parameter or apply an unphysical infrared cutoff. copyright 1996 The American Physical Society

  2. Self-consistent areas law in QCD

    International Nuclear Information System (INIS)

    Makeenko, Yu.M.; Migdal, A.A.

    1980-01-01

    The problem of obtaining the self-consistent areas law in quantum chromodynamics (QCD) is considered from the point of view of the quark confinement. The exact equation for the loop average in multicolor QCD is reduced to a bootstrap form. Its iterations yield new manifestly gauge invariant perturbation theory in the loop space, reproducing asymptotic freedom. For large loops, the areas law apprears to be a self-consistent solution

  3. Search for the QCD ground state

    International Nuclear Information System (INIS)

    Reuter, M.; Wetterich, C.

    1994-05-01

    Within the Euclidean effective action approach we propose criteria for the ground state of QCD. Despite a nonvanishing field strength the ground state should be invariant with respect to modified Poincare transformations consisting of a combination of translations and rotations with suitable gauge transformations. We have found candidate states for QCD with four or more colours. The formation of gluon condensates shows similarities with the Higgs phenomenon. (orig.)

  4. Recent developments in QCD for LHC physics

    International Nuclear Information System (INIS)

    Anastasiou, C.

    2006-01-01

    We will review recent theoretical developments in QCD, attempting to assess the phenomenological impact of new theoretical results and to identify potentially useful directions for the future. A part of the talk will be devoted to new imaginative ideas which are rapidly changing the traditional approach to QCD computations, and surprising theoretical discoveries from perturbative calculations on the structure of gauge theories. (author)

  5. The topology of gauge fields

    International Nuclear Information System (INIS)

    Tellis, D.R.

    2000-01-01

    Full text: Instantons in pure Yang-Mills gauge theory have been studied extensively by physicists and mathematicians alike. The surprisingly rich topological structure plays an important role in hadron structure. A crucial role is played by how the boundary conditions on the gauge fields are imposed. While the topology of gauge fields in pure Yang-Mills gauge theory is understood for the compact manifold of the 4-sphere, the manifold of the 4-torus remains an active area of study. The latter is particularly important in the study of Lattice QCD

  6. Light relativistic bound states in high temperature QCD

    International Nuclear Information System (INIS)

    Zahed, Ismail

    1991-01-01

    The nonperturbative structure of high temperature QCD is combined with generalized sum-rules arguments to analyse gauge invariant correlation functions in real time. It is shown that for a plausible choice of condensates, QCD at high temperature exhibits color singlet excitations as opposed to merely screened quarks and gluons. (author). 14 refs.; 2 figs

  7. Canonical quantization of the generalized axial gauge

    International Nuclear Information System (INIS)

    Haller, K.

    1990-01-01

    The incompatibility of the constraint A 3 =0 with canonical commutation rules is discussed. A canonical formulation is given of QED and QCD in the axial gauge with n 1 =n 2 =0, n 3 =α and n 0 =β, where α and β are arbitrary real numbers. A Hilbert space is established for the perturbative theory, and a propagator is derived by obtaining an expression for the interaction picture gauge fields, and evaluating the vacuum expectation value of its time-ordered products in the perturbative vacuum. The propagator is expressed in terms of the parameter γ=α/β and is shown to reproduce the light cone gauge propagator when γ=1, and the temporal gauge propagator when γ=0, accommodating various prescriptions for the spurious propagator pole, including the Mandelstam-Leibbrandt and principal value prescriptions. When γ→∞, the generalized axial gauge propagator leads to an expression for the propagator in the A 3 =0 gauge, though in that case the order in which the integration over k 0 is performed, and the limit γ→∞ is taken, affects the resulting expression. Another Hilbert space is established, in which the constraints that include all interactions are implemented in a time independent fashion. It is pointed out that this Hilbert space, and the Hilbert space of the perturbative theory are unitarily equivalent in QED, but that they cannot be unitarily equivalent in QCD. Implications of this fact for the nonperturbative states of QCD are discussed. (orig.)

  8. Gauge-fixing ambiguity and monopole number

    International Nuclear Information System (INIS)

    Hioki, S.; Miyamura, O.

    1991-01-01

    Gauge-fixing ambiguities of lattice SU(2) QCD are studied in the maximally abelian and unitary gauges. In the former, we find local maxima of a gauge-fixing function which may correspond to Gribov copies. There is a definite anti-correlation between the number of monopoles and the value of the function. Errors of measured quantities coming from the ambiguity are found to be less than inherent dispersion in the ensemble average. No ambiguity is found in the unitary gauges. (orig.)

  9. QCD on the light cone

    International Nuclear Information System (INIS)

    Brodsky, S.J.

    1992-09-01

    The quantization of gauge theory at fixed light-cone time τ = t - z/c provides new perspectives for solving non-perturbative problems in quantum chromodynamics. The light-cone Fock state expansion provides both a precise definition of the relativistic wavefunctions of hadrons as bound-states of quarks and gluons and a general calculus for predicting QCD processes at the amplitude level. Applications to exclusive processes and weak decay amplitudes are discussed. The problem of computing the hadronic spectrum and the corresponding light-cone wavefunctions of QCD in one space and one time dimension has been successfully reduced to the diagonalization of a discrete representation of the light-cone Hamiltonian. The problems confronting the solution of gauge theories in 3 + 1 dimensions in the light-cone quantization formalism,, including zero modes and non-perturbative renormalization, are reviewed

  10. Exactly soluble QCD and confinement of quarks

    International Nuclear Information System (INIS)

    Rusakov, B.

    1997-01-01

    An exactly soluble non-perturbative model of the pure gauge QCD is derived as a weak coupling limit of the lattice theory in plaquette formulation [B. Rusakov, Phys. Lett. B 398 (1997) 331]. The model represents QCD as a theory of the weakly interacting field strength fluxes. The area law behavior of the Wilson loop average is a direct result of this representation: the total flux through macroscopic loop is the additive (due to the weakness of the interaction) function of the elementary fluxes. The compactness of the gauge group is shown to be the factor which prevents the elementary fluxes contributions from cancellation. There is no area law in the non-compact theory. (orig.)

  11. Analytic stochastic regularization: gauge and supersymmetry theories

    International Nuclear Information System (INIS)

    Abdalla, M.C.B.

    1988-01-01

    Analytic stochastic regularization for gauge and supersymmetric theories is considered. Gauge invariance in spinor and scalar QCD is verified to brak fown by an explicit one loop computation of the two, theree and four point vertex function of the gluon field. As a result, non gauge invariant counterterms must be added. However, in the supersymmetric multiplets there is a cancellation rendering the counterterms gauge invariant. The calculation is considered at one loop order. (author) [pt

  12. Topological resolution of gauge theory singularities

    Science.gov (United States)

    Saracco, Fabio; Tomasiello, Alessandro; Torroba, Gonzalo

    2013-08-01

    Some gauge theories with Coulomb branches exhibit singularities in perturbation theory, which are usually resolved by nonperturbative physics. In string theory this corresponds to the resolution of timelike singularities near the core of orientifold planes by effects from F or M theory. We propose a new mechanism for resolving Coulomb branch singularities in three-dimensional gauge theories, based on Chern-Simons interactions. This is illustrated in a supersymmetric SU(2) Yang-Mills-Chern-Simons theory. We calculate the one-loop corrections to the Coulomb branch of this theory and find a result that interpolates smoothly between the high-energy metric (that would exhibit the singularity) and a regular singularity-free low-energy result. We suggest possible applications to singularity resolution in string theory and speculate a relationship to a similar phenomenon for the orientifold six-plane in massive IIA supergravity.

  13. Topological resolution of gauge theory singularities

    Energy Technology Data Exchange (ETDEWEB)

    Saracco, Fabio; Tomasiello, Alessandro; Torroba, Gonzalo

    2013-08-21

    Some gauge theories with Coulomb branches exhibit singularities in perturbation theory, which are usually resolved by nonperturbative physics. In string theory this corresponds to the resolution of timelike singularities near the core of orientifold planes by effects from F or M theory. We propose a new mechanism for resolving Coulomb branch singularities in three-dimensional gauge theories, based on Chern-Simons interactions. This is illustrated in a supersymmetric S U ( 2 ) Yang-Mills-Chern-Simons theory. We calculate the one-loop corrections to the Coulomb branch of this theory and find a result that interpolates smoothly between the high-energy metric (that would exhibit the singularity) and a regular singularity-free low-energy result. We suggest possible applications to singularity resolution in string theory and speculate a relationship to a similar phenomenon for the orientifold six-plane in massive IIA supergravity.

  14. Properties of quark matter governed by quantum chromodynamics. Pt. 2

    International Nuclear Information System (INIS)

    Soni, V.

    1983-01-01

    Renormalization schemes are examined (in the Coulomb gauge) for quantum chromodynamics in the presence of quark matter. We demand that the effective coupling constant for all schemes become congruent with the vacuum QCD running coupling constant as the matter chemical potential, μ, goes to zero. Also, to enable us to standardize with the vacuum QCD running coupling constant at some asymptotic momentum transfer, vertical strokep 0 vertical stroke, we keep μ 0 vertical stroke, to ensure that the matter contribution is negligible at this point. This means all schemes merge with vacuum QCD at vertical strokep 0 vertical stroke and beyond. Two renormalization group invariants are shown to emerge: (I) the effective or invariant charge, gsub(inv) 2 , which is, however, scheme dependent and (II) g 2 (M)/S(M), where S(M) - 1 is the Coulomb propagator, which is scheme independent. The only scheme in which gsub(inv) 2 is scheme independent and identical to g 2 (M)/S(M) is the screened charged scheme (previous paper) characterised by the normalization of the entire Green function, S - 1 , to unity. We conclude that this is the scheme to be used if one wants to identify with the experimental effective coupling in perturbation theory. However, if we do not restrict to perturbation theory all schemes should be allowed. Although we discuss matter QCD in the Coulomb gauge, the above considerations are quite general to gauge theories in the presence of matter. (orig.)

  15. Adler's theorem in finite massless QED and possible extensions to non-Abelian gauge theories. II

    International Nuclear Information System (INIS)

    Bernstein, J.

    1975-01-01

    The indefinite metric produced by the ghost fields in the Coulomb gauge in Yang-Mills theories is discussed. It is shown that the ghosts greatly complicate the job of proving, or disproving, an Adler theorem in this gauge. An old result of Schwinger for Coulomb gauge Yang-Mills theories is also found to be compromised by ghosts. (Auth.)

  16. High-loop perturbative renormalization constants for Lattice QCD (III): three-loop quark currents for Iwasaki gauge action and n{sub f} = 4 Wilson fermions

    Energy Technology Data Exchange (ETDEWEB)

    Brambilla, M.; Di Renzo, F. [Universita di Parma (Italy); INFN, Gruppo Collegato di Parma, Dipartimento di Fisica e Scienze della Terra, Parma (Italy); Hasegawa, M. [Universita di Parma (Italy); Bogoliubov Laboratory of Theoretical Physics, Dubna (Russian Federation); INFN, Gruppo Collegato di Parma, Dipartimento di Fisica e Scienze della Terra, Parma (Italy)

    2014-07-15

    This is the third of a series of papers on three-loop computation of renormalization constants for Lattice QCD. Our main points of interest are results for the regularization defined by the Iwasaki gauge action and n{sub f} Wilson fermions. Our results for quark bilinears renormalized according to the RI'-MOM scheme can be compared to non-perturbative results. The latter are available for twisted mass QCD: being defined in the chiral limit, the renormalization constants must be the same. We also address more general problems. In particular, we discuss a few methodological issues connected to summing the perturbative series such as the effectiveness of boosted perturbation theory and the disentanglement of irrelevant and finite-volume contributions. Discussing these issues we consider not only the new results of this paper, but also those for the regularization defined by the tree-level Symanzik improved gauge action and n{sub f} Wilson fermions, which we presented in a recent paper of ours. We finally comment on the extent to which the techniques we put at work in the NSPT context can provide a fresher look into the lattice version of the RI'-MOM scheme. (orig.)

  17. The infrared behaviour of QCD Green's functions. Confinement, dynamical symmetry breaking, and hadrons as relativistic bound states

    Science.gov (United States)

    Alkofer, Reinhard; von Smekal, Lorenz

    2001-11-01

    Recent studies of QCD Green's functions and their applications in hadronic physics are reviewed. We discuss the definition of the generating functional in gauge theories, in particular, the rôle of redundant degrees of freedom, possibilities of a complete gauge fixing versus gauge fixing in presence of Gribov copies, BRS invariance and positivity. The apparent contradiction between positivity and colour antiscreening in combination with BRS invariance in QCD is considered. Evidence for the violation of positivity by quarks and transverse gluons in the covariant gauge is collected, and it is argued that this is one manifestation of confinement. We summarise the derivation of the Dyson-Schwinger equations (DSEs) of QED and QCD. For the latter, the implications of BRS invariance on the Green's functions are explored. The possible influence of instantons on DSEs is discussed in a two-dimensional model. In QED in (2+1) and (3+1) dimensions, the solutions for Green's functions provide tests of truncation schemes which can under certain circumstances be extended to the DSEs of QCD. We discuss some limitations of such extensions and assess the validity of assumptions for QCD as motivated from studies in QED. Truncation schemes for DSEs are discussed in axial and related gauges, as well as in the Landau gauge. Furthermore, we review the available results from a systematic non-perturbative expansion scheme established for Landau gauge QCD. Comparisons to related lattice results, where available, are presented. The applications of QCD Green's functions to hadron physics are summarised. Properties of ground state mesons are discussed on the basis of the ladder Bethe-Salpeter equation for quarks and antiquarks. The Goldstone nature of pseudoscalar mesons and a mechanism for diquark confinement beyond the ladder approximation are reviewed. We discuss some properties of ground state baryons based on their description as Bethe-Salpeter/Faddeev bound states of quark

  18. Regularization of the light-cone gauge gluon propagator singularities using sub-gauge conditions

    Energy Technology Data Exchange (ETDEWEB)

    Chirilli, Giovanni A.; Kovchegov, Yuri V.; Wertepny, Douglas E. [Department of Physics, The Ohio State University,191 W Woodruff Ave, Columbus, OH 43210 (United States)

    2015-12-21

    Perturbative QCD calculations in the light-cone gauge have long suffered from the ambiguity associated with the regularization of the poles in the gluon propagator. In this work we study sub-gauge conditions within the light-cone gauge corresponding to several known ways of regulating the gluon propagator. Using the functional integral calculation of the gluon propagator, we rederive the known sub-gauge conditions for the θ-function gauges and identify the sub-gauge condition for the principal value (PV) regularization of the gluon propagator’s light-cone poles. The obtained sub-gauge condition for the PV case is further verified by a sample calculation of the classical Yang-Mills field of two collinear ultrarelativistic point color charges. Our method does not allow one to construct a sub-gauge condition corresponding to the well-known Mandelstam-Leibbrandt prescription for regulating the gluon propagator poles.

  19. Two-color lattice QCD with staggered quarks

    Energy Technology Data Exchange (ETDEWEB)

    Scheffler, David

    2015-07-20

    The study of quantum chromodynamics (QCD) at finite temperature and density provides important contributions to the understanding of strong-interaction matter as it is present e.g. in nuclear matter and in neutron stars or as produced in heavy-ion collision experiments. Lattice QCD is a non-perturbative approach, where equations of motion for quarks and gluons are discretized on a finite space-time lattice. The method successfully describes the behavior of QCD in the vacuum and at finite temperature, however it cannot be applied to finite baryon density due to the fermion sign problem. Various QCD-like theories, that offer to draw conclusions about QCD, allow simulations also at finite densities. In this work we investigate two-color QCD as a popular example of a QCD-like theory free from the sign problem with methods from lattice gauge theory. For the generation of gauge configurations with two dynamical quark flavors in the staggered formalism with the ''rooting trick'' we apply the Rational Hybrid Monte Carlo (RHMC) algorithm. We carry out essential preparatory work for future simulations at finite density. As a start, we concentrate on the calculation of the effective potential for the Polyakov loop, which is an order parameter for the confinement-deconfinement transition, in dependence of the temperature and quark mass. It serves as an important input for effective models of QCD. We obtain the effective potential via the histogram method from local distributions of the Polyakov loop. To study the influence of dynamical quarks on gluonic observables, the simulations are performed with large quark masses and are compared to calculations in the pure gauge theory. In the second part of the thesis we examine aspects of the chiral phase transition along the temperature axis. The symmetry group of chiral symmetry in two-color QCD is enlarged to SU(2N{sub f}). Discretized two-color QCD in the staggered formalism exhibits a chiral symmetry breaking

  20. The Nielsen identities for the two-point functions of QED and QCD

    International Nuclear Information System (INIS)

    Breckenridge, J.C.; Sasketchewan Univ., Saskatoon, SK; Lavelle, M.J.; Steele, T.G.; Sasketchewan Univ., Saskatoon, SK

    1995-01-01

    We consider the Nielsen identities for the two-point functions of full QCD and QED in the class of Lorentz gauges. For pedagogical reasons the identities are first derived in QED to demonstrate the gauge independence of the photon self-energy, and of the electron mass shell. In QCD we derive the general identity and hence the identities for the quark, gluon and ghost propagators. The explicit contributions to the gluon and ghost identities are calculated to one-loop order, and then we show that the quark identity requires that in on-shell schemes the quark mass renormalisation must be gauge independent. Furthermore, we obtain formal solutions for the gluon self-energy and ghost propagator in terms of the gauge dependence of other, independent Green functions. (orig.)

  1. Gauge theories and monopoles

    International Nuclear Information System (INIS)

    Cabibbo, N.

    1983-01-01

    This chapter attempts to present some of the fundamental geometrical ideas at the basis of gauge theories. Describes Dirac Monopoles and discusses those ideas that are not usually found in more ''utilitarian'' presentations which concentrate on QCD or on the Glashow-Salam-Weinberg model. This topic was chosen because of the announcement of the possible detection of a Dirac monopole. The existence of monopoles depends on topological features of gauge theories (i.e., on global properties of field configurations which are unique to gauge theories). Discusses global symmetry-local symmetry; the connection; path dependence and the gauge fields; topology and monopoles; the case of SU(3) x U(1); and the 't Hooft-Polyakov monopole

  2. Quenching parameter in a holographic thermal QCD

    Science.gov (United States)

    Patra, Binoy Krishna; Arya, Bhaskar

    2017-01-01

    We have calculated the quenching parameter, q ˆ in a model-independent way using the gauge-gravity duality. In earlier calculations, the geometry in the gravity side at finite temperature was usually taken as the pure AdS black hole metric for which the dual gauge theory becomes conformally invariant unlike QCD. Therefore we use a metric which incorporates the fundamental quarks by embedding the coincident D7 branes in the Klebanov-Tseytlin background and a finite temperature is switched on by inserting a black hole into the background, known as OKS-BH metric. Further inclusion of an additional UV cap to the metric prepares the dual gauge theory to run similar to thermal QCD. Moreover q ˆ is usually defined in the literature from the Glauber model perturbative QCD evaluation of the Wilson loop, which has no reasons to hold if the coupling is large and is thus against the main idea of gauge-gravity duality. Thus we use an appropriate definition of q ˆ : q ˆ L- = 1 /L2, where L is the separation for which the Wilson loop is equal to some specific value. The above two refinements cause q ˆ to vary with the temperature as T4 always and to depend linearly on the light-cone time L- with an additional (1 /L-) correction term in the short-distance limit whereas in the long-distance limit, q ˆ depends only linearly on L- with no correction term. These observations agree with other holographic calculations directly or indirectly.

  3. Lattice gauge theories

    International Nuclear Information System (INIS)

    Hasenfratz, A.; Hasenfratz, P.

    1985-01-01

    This paper deals almost exclusively with applications in QCD. Presumably QCD will remain in the center of lattice calculations in the near future. The existing techniques and the available computer resources should be able to produce trustworthy results in pure SU(3) gauge theory and in quenched hadron spectroscopy. Going beyond the quenched approximation might require some technical breakthrough or exceptional computer resources, or both. Computational physics has entered high-energy physics. From this point of view, lattice QCD is only one (although the most important, at present) of the research fields. Increasing attention is devoted to the study of other QFTs. It is certain that the investigation of nonasymptotically free theories, the Higgs phenomenon, or field theories that are not perturbatively renormalizable will be important research areas in the future

  4. PT Symmetry and QCD: Finite Temperature and Density

    Directory of Open Access Journals (Sweden)

    Michael C. Ogilvie

    2009-04-01

    Full Text Available The relevance of PT symmetry to quantum chromodynamics (QCD, the gauge theory of the strong interactions, is explored in the context of finite temperature and density. Two significant problems in QCD are studied: the sign problem of finite-density QCD, and the problem of confinement. It is proven that the effective action for heavy quarks at finite density is PT-symmetric. For the case of 1+1 dimensions, the PT-symmetric Hamiltonian, although not Hermitian, has real eigenvalues for a range of values of the chemical potential μ, solving the sign problem for this model. The effective action for heavy quarks is part of a potentially large class of generalized sine-Gordon models which are non-Hermitian but are PT-symmetric. Generalized sine-Gordon models also occur naturally in gauge theories in which magnetic monopoles lead to confinement. We explore gauge theories where monopoles cause confinement at arbitrarily high temperatures. Several different classes of monopole gases exist, with each class leading to different string tension scaling laws. For one class of monopole gas models, the PT-symmetric affine Toda field theory emerges naturally as the effective theory. This in turn leads to sine-law scaling for string tensions, a behavior consistent with lattice simulations.

  5. Renormalization group approach to QCD phase transitions

    International Nuclear Information System (INIS)

    Midorikawa, S.; Yoshimoto, S.; So, H.

    1987-01-01

    Effective scalar theories for QCD are proposed to investigate the deconfining and chiral phase transitions. The orders of the phase transitions are determined by infrared stabilities of the fixed points. It is found that the transitions in SU(3) gauge theories are of 1st order for any number of massless flavors. The cases of SU(2) and SU(4) gauge theories are also discussed. (orig.)

  6. Renormalizable Abelian-projected effective gauge theory derived from quantum chromodynamics

    International Nuclear Information System (INIS)

    Kondo, Kei-ichi; Shinohara, Toru

    2001-01-01

    We show that an effective Abelian gauge theory can be obtained as a renormalizable theory from QCD in the maximal Abelian gauge. The derivation improves in a systematic manner the previous version that was obtained by one of the authors and was referred to as the Abelian-projected effective gauge theory. This result supports the view that we can construct an effective Abelian gauge theory from QCD without losing characteristic features of the original non-Abelian gauge theory. In fact, it is shown that the effective coupling constant in the resulting renormalizable theory has a renormalization-scale dependence governed by the β-function that is exactly the same as that of the original Yang-Mills theory, irrespective of the choice of gauge fixing parameters of the maximal Abelian gauge and the parameters used for identifying the dual variables. Moreover, we evaluate the anomalous dimensions of the fields and parameters in the resultant theory. By choosing the renormalized parameters appropriately, we can switch the theory into an electric or a magnetic theory. (author)

  7. Lattice gauge theory using parallel processors

    International Nuclear Information System (INIS)

    Lee, T.D.; Chou, K.C.; Zichichi, A.

    1987-01-01

    The book's contents include: Lattice Gauge Theory Lectures: Introduction and Current Fermion Simulations; Monte Carlo Algorithms for Lattice Gauge Theory; Specialized Computers for Lattice Gauge Theory; Lattice Gauge Theory at Finite Temperature: A Monte Carlo Study; Computational Method - An Elementary Introduction to the Langevin Equation, Present Status of Numerical Quantum Chromodynamics; Random Lattice Field Theory; The GF11 Processor and Compiler; and The APE Computer and First Physics Results; Columbia Supercomputer Project: Parallel Supercomputer for Lattice QCD; Statistical and Systematic Errors in Numerical Simulations; Monte Carlo Simulation for LGT and Programming Techniques on the Columbia Supercomputer; Food for Thought: Five Lectures on Lattice Gauge Theory

  8. 56. annual symposium of the Austrian Physical Society. Abstracts

    International Nuclear Information System (INIS)

    Ernst, W.E.; Neger, T.

    2006-01-01

    Full text: This annual symposium provides an overview of advances on the following subjects: acoustics; atomic, molecular and plasma physics; solid state physics; physics history; nuclear and particle physics; biophysics, medical, and environmental physics; neutrons and synchrotron radiation physics; surface and thin film; energy industry; polymer physics; quantum electronics, electrodynamics and optics. Specific topics such as the application of transmission electron microscopy, monochromated scanning transmission electron microscopy, mass spectrometry (accelerator mass spectrometry), proton induced x-ray emission (PIXE), leakage radiation microscopy, synchrotron radiation, scanning tunneling microscopes, matter wave interferometry, neutron diffraction, neutron holography, neutron scattering and ultra small scattering in the analysis of nanomaterials and biomaterials were discussed as well as others dealing with atoms excitation and depletion, Coulomb gauge QCD; Coulomb lattice; Coulomb landau gauge; hyperfine structure, lattice field theory, quantum mechanics, particle interactions, QCD, lattice QCD, quantum chemistry, quantum cryptography, quantum entanglement, ion-surface collisions, air traffic pollutants, ultra short pulsed lasers, VOC seasonal variations, surfaces oxidation, magnetic thin films, ATLAS calorimeter system, LHC (lepton flavor violation, radiation loses, beam-beam interactions). Those contributions which are in the INIS subject scope are indexed individually. (nevyjel)

  9. Phenomenological dynamics in QCD at large distances

    International Nuclear Information System (INIS)

    Gogohia, V.Sh.; Kluge, Gy.

    1991-07-01

    A gauge-invariant, nonperturbative approach to QCD at large distances in the context of the Schwinger-Dyson equations and corresponding Slavnov-Taylor identities in the quark sector is presented. Making only one widely accepted assumption that the full gluon propagator becomes an infrared singular like (q 2 ) -2 in the covariant gauge, we find three and only three confinement-type solutions for the quark propagator (quark confinement theorem.) The approach is free from ghost complications. Also show that multiplication by the quark infrared renormalization constant only, would make all the Green's functions infrared finite (multiplicative renormalizability). The bound-state problem in framework of Bethe-Salpeter equation is discussed as well. Some basic physical parameters of chiral QCD as pion decay constant and quark condensate, have been calculated within our approach. (author) 75 refs.; 14 figs

  10. Conformal Gauge-Yukawa Theories away From Four Dimensions

    DEFF Research Database (Denmark)

    Codello, Alessandro; Langaeble, Kasper; Litim, Daniel

    2016-01-01

    We present the phase diagram and associated fixed points for a wide class of Gauge-Yukawa theories in $d=4+\\epsilon$ dimensions. The theories we investigate involve non-abelian gauge fields, fermions and scalars in the Veneziano-Witten limit. The analysis is performed in steps, we start with QCD$...

  11. Adler's theorem in finite massless QED and possible extensions to non- Abelian gauge theories II

    CERN Document Server

    Bernstein, J

    1975-01-01

    For pt.I see ibid., vol.B95, p.461 (1975). The indefinite metric produced by the ghost fields in the Coulomb gauge in Yang-Mills theories is discussed. It is shown that the ghosts greatly complicate the job of proving, or disproving, an Adler theorem in this gauge. An old result of Schwinger (1962) for Coulomb gauge Yang-Mills theories is also found to be compromised by ghosts. (7 refs).

  12. QCD and strongly coupled gauge theories: challenges and perspectives

    CERN Document Server

    Brambilla, N.; Foka, P.; Gardner, S.; Kronfeld, A.S.; Alford, M.G.; Alkofer, R.; Butenschoen, M.; Cohen, T.D.; Erdmenger, J.; Fabbietti, L.; Faber, M.; Goity, J.L.; Ketzer, B.; Lin, H.W.; Llanes-Estrada, F.J.; Meyer, H.B.; Pakhlov, P.; Pallante, E.; Polikarpov, M.I.; Sazdjian, H.; Schmitt, A.; Snow, W.M.; Vairo, A.; Vogt, R.; Vuorinen, A.; Wittig, H.; Arnold, P.; Christakoglou, P.; Di Nezza, P.; Fodor, Z.; Garcia i Tormo, X.; Hollwieser, R.; Janik, M.A.; Kalweit, A.; Keane, D.; Kiritsis, E.; Mischke, A.; Mizuk, R.; Odyniec, G.; Papadodimas, K.; Pich, A.; Pittau, R.; Qiu, J.W.; Ricciardi, G.; Salgado, C.A.; Schwenzer, K.; Stefanis, N.G.; von Hippel, G.M.; Zakharov, V.I.

    2014-10-21

    We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly-coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.

  13. Three-Dimensional Gauge Theories and ADE Monopoles

    OpenAIRE

    Tong, David

    1998-01-01

    We study three-dimensional N=4 gauge theories with product gauge groups constructed from ADE Dynkin diagrams. One-loop corrections to the metric on the Coulomb branch are shown to coincide with the metric on the moduli space of well-seperated ADE monopoles. We propose that this correspondence is exact.

  14. QCD and collider physics

    CERN Document Server

    Stirling, William James

    1991-12-01

    1. Some basic theory. 2. Two important applications: - e+ e- annihilation (LEPSLS) ; deep inelastic scattering (HERA). 3. Other applications..., large Pt jets, W and Z, heavy quark production..., (pp- colliders). In this lecture: some basic theory. 1. QCD as a non abelian gauge field theory. 2. Asymptotic freedom. 3. Beyond leading order - renormalisation schemes. 4. MS.

  15. Exceptional confinement in G(2) gauge theory

    International Nuclear Information System (INIS)

    Holland, K.; Minkowski, P.; Pepe, M.; Wiese, U.-J.

    2003-01-01

    We study theories with the exceptional gauge group G(2). The 14 adjoint 'gluons' of a G(2) gauge theory transform as {3}, {3-bar} and {8} under the subgroup SU(3), and hence have the color quantum numbers of ordinary quarks, anti-quarks and gluons in QCD. Since G(2) has a trivial center, a 'quark' in the {7} representation of G(2) can be screened by 'gluons'. As a result, in G(2) Yang-Mills theory the string between a pair of static 'quarks' can break. In G(2) QCD there is a hybrid consisting of one 'quark' and three 'gluons'. In supersymmetric G(2) Yang-Mills theory with a {14} Majorana 'gluino' the chiral symmetry is Z(4) χ . Chiral symmetry breaking gives rise to distinct confined phases separated by confined-confined domain walls. A scalar Higgs field in the {7} representation breaks G(2) to SU(3) and allows us to interpolate between theories with exceptional and ordinary confinement. We also present strong coupling lattice calculations that reveal basic features of G(2) confinement. Just as in QCD, where dynamical quarks break the Z(3) symmetry explicitly, G(2) gauge theories confine even without a center. However, there is not necessarily a deconfinement phase transition at finite temperature

  16. Towards an effective bilocal theory from QCD in a background

    International Nuclear Information System (INIS)

    Magpantay, J.A.

    1982-05-01

    Using the path integral, we show how we can get background gauge invariant bilocals (to be identified with mesons) from QCD in a nontrivial ground state. We discuss in this paper mainly the formal manipulations, especially how to deal with the zero modes. We also discuss the large N limit of QCD in a background. (author)

  17. The AdS/QCD correspondence: still undelivered

    International Nuclear Information System (INIS)

    Csaki, Csaba; Reece, Matthew; Terning, John

    2009-01-01

    We consider the particle spectrum and event shapes in large N gauge theories in different regimes of the short-distance 't Hooft coupling, λ. The mesons in the small λ limit should have a Regge spectrum in order to agree with perturbation theory, while generically the large λ theories with gravity duals produce spectra reminiscent of KK modes. We argue that these KK-like states are qualitatively different from QCD modes: they are deeply bound states which are sensitive to short distance interactions rather than the flux tube-like states expected in asymptotically free, confining gauge theories. In addition, we also find that the characteristic event shapes for the large λ theories with gravity duals are close to spherical, very different from QCD-like (small λ, small N) and Nambu-Goto-like (small λ, large N) theories which have jets. This observation is in agreement with the conjecture of Strassler on event shapes in large 't Hooft coupling theories, which was recently proved by Hofman and Maldacena for the conformal case. This conclusion does not change even when considering soft-wall backgrounds for the gravity dual. The picture that emerges is the following: theories with small and large λ are qualitatively different, while theories with small and large N are qualitatively similar. Thus it seems that it is the relative smallness of the 't Hooft coupling in QCD that prevents a reliable AdS/QCD correspondence from emerging, and that reproducing characteristic QCD-like behavior will require genuine stringy dynamics to be incorporated into any putative dual theory.

  18. γN → Δ transition form factors in quenched and NF = 2 QCD

    International Nuclear Information System (INIS)

    Alexandrou, C.; Forcrand, Ph. de; Lippert, Th.; Neff, H.; Negele, J.W.; Schilling, K.; Schroers, W.; Tsapalis, A.

    2004-01-01

    Calculations of the magnetic dipole, electric quadrupole and Coulomb quadrupole amplitudes for the transition γN → Δ are presented both in quenched QCD and with two flavours of degenerate dynamical quarks

  19. Pure Gauge theory in crystal lattice and Coulomb gases

    International Nuclear Information System (INIS)

    Marchetti, D.H.U.

    1985-01-01

    A method for the construction of classical gases, starting from a pure gauge theory, is described. The method is applied to the U(1) gauge theory in two spatial dimensions. For this model it's seen the vaccua appearing as a consequence of the quantization ambiguity. The connection between the vaccua and the confinement is discussed. (Author) [pt

  20. Coherent-state representation for the QCD ground state

    International Nuclear Information System (INIS)

    Celenza, L.S.; Ji, C.; Shakin, C.M.

    1987-01-01

    We make use of the temporal gauge to construct a coherent state which is meant to describe the gluon condensate in the QCD vacuum under the assumption that the condensate is in a zero-momentum mode. The state so constructed is a color singlet and will yield finite, nonperturbative vacuum expectation values such as . (This matrix element is found to have a value of about 0.012 GeV 4 in QCD sum-rule studies.)

  1. Cosmologically safe QCD axion without fine-tuning

    International Nuclear Information System (INIS)

    Yamada, Masaki; Yanagida, Tsutomu T.; Yonekura, Kazuya

    2015-10-01

    Although QCD axion models are widely studied as solutions to the strong CP problem, they generically confront severe fine-tuning problems to guarantee the anomalous PQ symmetry. In this letter, we propose a simple QCD axion model without any fine-tunings. We introduce an extra dimension and a pair of extra quarks living on two branes separately, which is also charged under a bulk Abelian gauge symmetry. We assume a monopole condensation on our brane at an intermediate scale, which implies that the extra quarks develop the chiral symmetry breaking and the PQ symmetry is broken. In contrast to the original Kim's model, our model explains the origin of the PQ symmetry thanks to the extra dimension and avoids the cosmological domain wall problem because of the chiral symmetry breaking in the Abelian gauge theory.

  2. Scaling violation in QCD

    International Nuclear Information System (INIS)

    Furmanski, W.

    1981-08-01

    The effects of scaling violation in QCD are discussed in the perturbative scheme, based on the factorization of mass singularities in the light-like gauge. Some recent applications including the next-to-leading corrections are presented (large psub(T) scattering, numerical analysis of the leptoproduction data). A proposal is made for extending the method on the higher twist sector. (author)

  3. Lattice QCD for Baryon Rich Matter – Beyond Taylor Expansions

    Energy Technology Data Exchange (ETDEWEB)

    Bornyakov, V. [ITEP, B. Cheremushkinskaya 25, Moscow, 117218 (Russian Federation); School of Biomedicine, Far Eastern Federal University, Sukhanova 8, Vladivostok 690950 (Russian Federation); Boyda, D. [School of Biomedicine, Far Eastern Federal University, Sukhanova 8, Vladivostok 690950 (Russian Federation); Goy, V. [School of Natural Sciences, Far Eastern Federal University, Sukhanova 8, Vladivostok 690950 (Russian Federation); Molochkov, A. [School of Biomedicine, Far Eastern Federal University, Sukhanova 8, Vladivostok 690950 (Russian Federation); Nakamura, A. [School of Biomedicine, Far Eastern Federal University, Sukhanova 8, Vladivostok 690950 (Russian Federation); Research Center for Nuclear Physics (RCNP), Osaka University, Ibaraki, Osaka, 567-0047 (Japan); Theoretical Research Division, Nishina Center, RIKEN, Wako 351-0198 (Japan); Nikolaev, A. [School of Biomedicine, Far Eastern Federal University, Sukhanova 8, Vladivostok 690950 (Russian Federation); Zakharov, V.I. [ITEP, B. Cheremushkinskaya 25, Moscow, 117218 (Russian Federation); School of Biomedicine, Far Eastern Federal University, Sukhanova 8, Vladivostok 690950 (Russian Federation); Moscow Inst Phys & Technol, Dolgoprudny, Moscow Region, 141700 (Russian Federation)

    2016-12-15

    We discuss our study for exploring the QCD phase diagram based on the lattice QCD. To go beyond the Taylor expansion and to reach higher density regions, we employ the canonical approach. In order to produce lattice data which meet experimental situation as much as possible, we propose a canonical approach with the charge and baryon number. We present our lattice QCD GPU code for this project which employs the clover improved Wilson fermions and Iwasaki gauge action to investigate pure imaginary chemical potential.

  4. Lattice QCD for Baryon Rich Matter – Beyond Taylor Expansions

    International Nuclear Information System (INIS)

    Bornyakov, V.; Boyda, D.; Goy, V.; Molochkov, A.; Nakamura, A.; Nikolaev, A.; Zakharov, V.I.

    2016-01-01

    We discuss our study for exploring the QCD phase diagram based on the lattice QCD. To go beyond the Taylor expansion and to reach higher density regions, we employ the canonical approach. In order to produce lattice data which meet experimental situation as much as possible, we propose a canonical approach with the charge and baryon number. We present our lattice QCD GPU code for this project which employs the clover improved Wilson fermions and Iwasaki gauge action to investigate pure imaginary chemical potential.

  5. Induced QCD I: theory

    Energy Technology Data Exchange (ETDEWEB)

    Brandt, Bastian B. [Institute for Theoretical Physics, Goethe-University of Frankfurt,60438 Frankfurt (Germany); Institute for Theoretical Physics, University of Regensburg,93040 Regensburg (Germany); Lohmayer, Robert; Wettig, Tilo [Institute for Theoretical Physics, University of Regensburg,93040 Regensburg (Germany)

    2016-11-14

    We explore an alternative discretization of continuum SU(N{sub c}) Yang-Mills theory on a Euclidean spacetime lattice, originally introduced by Budzcies and Zirnbauer. In this discretization the self-interactions of the gauge field are induced by a path integral over N{sub b} auxiliary boson fields, which are coupled linearly to the gauge field. The main progress compared to earlier approaches is that N{sub b} can be as small as N{sub c}. In the present paper we (i) extend the proof that the continuum limit of the new discretization reproduces Yang-Mills theory in two dimensions from gauge group U(N{sub c}) to SU(N{sub c}), (ii) derive refined bounds on N{sub b} for non-integer values, and (iii) perform a perturbative calculation to match the bare parameter of the induced gauge theory to the standard lattice coupling. In follow-up papers we will present numerical evidence in support of the conjecture that the induced gauge theory reproduces Yang-Mills theory also in three and four dimensions, and explore the possibility to integrate out the gauge fields to arrive at a dual formulation of lattice QCD.

  6. Nuclear physics from strong coupling QCD

    CERN Document Server

    Fromm, Michael

    2009-01-01

    The strong coupling limit (beta_gauge = 0) of QCD offers a number of remarkable research possibilities, of course at the price of large lattice artifacts. Here, we determine the complete phase diagram as a function of temperature T and baryon chemical potential mu_B, for one flavor of staggered fermions in the chiral limit, with emphasis on the determination of a tricritical point and on the T ~ 0 transition to nuclear matter. The latter is known to happen for mu_B substantially below the baryon mass, indicating strong nuclear interactions in QCD at infinite gauge coupling. This leads us to studying the properties of nuclear matter from first principles. We determine the nucleon-nucleon potential in the strong coupling limit, as well as masses m_A of nuclei as a function of their atomic number A. Finally, we clarify the origin of nuclear interactions at strong coupling, which turns out to be a steric effect.

  7. Quantum Link Models and Quantum Simulation of Gauge Theories

    International Nuclear Information System (INIS)

    Wiese, U.J.

    2015-01-01

    This lecture is about Quantum Link Models and Quantum Simulation of Gauge Theories. The lecture consists out of 4 parts. The first part gives a brief history of Computing and Pioneers of Quantum Computing and Quantum Simulations of Quantum Spin Systems are introduced. The 2nd lecture is about High-Temperature Superconductors versus QCD, Wilson’s Lattice QCD and Abelian Quantum Link Models. The 3rd lecture deals with Quantum Simulators for Abelian Lattice Gauge Theories and Non-Abelian Quantum Link Models. The last part of the lecture discusses Quantum Simulators mimicking ‘Nuclear’ physics and the continuum limit of D-Theorie models. (nowak)

  8. Non-perturbative Debye mass in finite-T QCD

    CERN Document Server

    Kajantie, Keijo; Peisa, J; Rajantie, A; Rummukainen, K; Shaposhnikov, Mikhail E

    1997-01-01

    Employing a non-perturbative gauge invariant definition of the Debye screening mass m_D in the effective field theory approach to finite T QCD, we use 3d lattice simulations to determine the leading O(g^2) and to estimate the next-to-leading O(g^3) corrections to m_D in the high temperature region. The O(g^2) correction is large and modifies qualitatively the standard power-counting hierarchy picture of correlation lengths in high temperature QCD.

  9. Simulations of QCD and QED with C* boundary conditions

    Science.gov (United States)

    Hansen, Martin; Lucini, Biagio; Patella, Agostino; Tantalo, Nazario

    2018-03-01

    We present exploratory results from dynamical simulations of QCD in isolation, as well as QCD coupled to QED, with C* boundary conditions. In finite volume, the use of C* boundary conditions allows for a gauge invariant and local formulation of QED without zero modes. In particular we show that the simulations reproduce known results and that masses of charged mesons can be extracted in a completely gauge invariant way. For the simulations we use a modified version of the HiRep code. The primary features of the simulation code are presented and we discuss some details regarding the implementation of C* boundary conditions and the simulated lattice action. Preprint: CP3-Origins-2017-046 DNRF90, CERN-TH-2017-214

  10. Novel QCD Phenomena

    International Nuclear Information System (INIS)

    Brodsky, Stanley J.; SLAC

    2007-01-01

    I discuss a number of novel topics in QCD, including the use of the AdS/CFT correspondence between Anti-de Sitter space and conformal gauge theories to obtain an analytically tractable approximation to QCD in the regime where the QCD coupling is large and constant. In particular, there is an exact correspondence between the fifth-dimension coordinate z of AdS space and a specific impact variable ζ which measures the separation of the quark constituents within the hadron in ordinary space-time. This connection allows one to compute the analytic form of the frame-independent light-front wavefunctions of mesons and baryons, the fundamental entities which encode hadron properties and allow the computation of exclusive scattering amplitudes. I also discuss a number of novel phenomenological features of QCD. Initial- and final-state interactions from gluon-exchange, normally neglected in the parton model, have a profound effect in QCD hard-scattering reactions, leading to leading-twist single-spin asymmetries, diffractive deep inelastic scattering, diffractive hard hadronic reactions, the breakdown of the Lam Tung relation in Drell-Yan reactions, and nuclear shadowing and non-universal antishadowing--leading-twist physics not incorporated in the light-front wavefunctions of the target computed in isolation. I also discuss tests of hidden color in nuclear wavefunctions, the use of diffraction to materialize the Fock states of a hadronic projectile and test QCD color transparency, and anomalous heavy quark effects. The presence of direct higher-twist processes where a proton is produced in the hard subprocess can explain the large proton-to-pion ratio seen in high centrality heavy ion collisions

  11. $\\gamma N \\to \\Delta$ transition form factors in Quenched and $N_F=2$ QCD

    CERN Document Server

    Alexandrou, C; Lippert, T; Neff, H; Negele, J W; Schilling, K; Schroers, W; Tsapalis, A; Forcrand, Ph. de; Lippert, Th.

    2003-01-01

    Calculations of the magnetic dipole, electric quadrupole and Coulomb quadrupole amplitudes for the transition $\\gamma N\\to \\Delta$ are presented both in quenched QCD and with two flavours of degenerate dynamical quarks.

  12. Coulomb correlations in many-electron systems on the level of self-consistent fields

    International Nuclear Information System (INIS)

    Warken, M.

    1991-06-01

    It was the aim of this thesis to show means and ways, in order to regard Coulomb correlation already on the SCF level. As mean to facilitate this general averaged fields should serve. For this first in chapter I was shown, how by means of suitable gauge fixings terms into effective potentials of the Hartree-Fock or g-Hartree type are introduced, which permit an interpretation as correlation density or as effective coupling constant. The following considerations were exemplarily performed on the cases g-Hartree (in Coulomb gauge) and on f-Hartree-Fock. (orig./HSI) [de

  13. A Unitary and Renormalizable Theory of the Standard Model in Ghost-Free Light-Cone Gauge

    Energy Technology Data Exchange (ETDEWEB)

    Brodsky, Stanley J.

    2002-02-15

    Light-front (LF) quantization in light-cone (LC) gauge is used to construct a unitary and simultaneously renormalizable theory of the Standard Model. The framework derived earlier for QCD is extended to the Glashow, Weinberg, and Salam (GWS) model of electroweak interaction theory. The Lorentz condition is automatically satisfied in LF-quantized QCD in the LC gauge for the free massless gauge field. In the GWS model, with the spontaneous symmetry breaking present, we find that the 't Hooft condition accompanies the LC gauge condition corresponding to the massive vector boson. The two transverse polarization vectors for the massive vector boson may be chosen to be the same as found in QCD. The non-transverse and linearly independent third polarization vector is found to be parallel to the gauge direction. The corresponding sum over polarizations in the Standard model, indicated by K{sub {mu}{nu}}(k); has several simplifying properties similar to the polarization sum D{sub {mu}{nu}}(k) in QCD. The framework is ghost-free, and the interaction Hamiltonian of electroweak theory can be expressed in a form resembling that of covariant theory, except for few additional instantaneous interactions which can be treated systematically. The LF formulation also provides a transparent discussion of the Goldstone Boson (or Electroweak) Equivalence Theorem, as the illustrations show.

  14. Small-x physics in perturbative QCD

    International Nuclear Information System (INIS)

    Lipatov, L.N.

    1996-07-01

    We review the parton model and the Regge approach to the QCD description of the deep-inelastic ep scattering at the small Bjorken variable x and demonstrate their relation with the DGLAP and BFKL evolution equations. It is shown, that in the leading logarithmic approximation the gluon is reggeized and the pomeron is a compound state of two reggeized gluons. The conformal invariance of the BFKL pomeron in the impact parameter space is used to investigate the scattering amplitudes at high energies and fixed momentum transfers. The remarkable properties of the Schroedinger equation for compound states of an arbitrary number of reggeized gluons in the multi-colour QCD are reviewed. The gauge-invariant effective action describing the gluon-Reggeon interactions is constructed. The known next-to-leading corrections to the QCD pomeron are discussed. (orig.)

  15. Elementary amplitudes from full QCD and the stochastic vacuum model

    International Nuclear Information System (INIS)

    Martini, A.F.; Menon, M.J.

    2002-01-01

    In a previous work, making use of the gluon gauge-invariant two-point correlation function determined from lattice QCD in the quenched approximation and the stochastic vacuum model, we determined the elementary (parton-parton) scattering amplitude in the momentum transfer space. In this communication we compute the elementary amplitude from new lattice QCD calculations that include the effects of dynamical fermions (full QCD). The main conclusion is that the inclusion of dynamical fermions leads to a normalized elementary amplitude that decreases more quickly with the momentum transfer than that in the quenched approximation. (author)

  16. Perturbation theory in light-cone gauge

    International Nuclear Information System (INIS)

    Vianello, Eliana

    2000-01-01

    Perturbation calculations are presented for the light-cone gauge Schwinger model. Eigenstates can be calculated perturbatively but the perturbation theory is nonstandard. We hope to extend the work to QCD 2 to resolve some outstanding issues in those theories

  17. Instantons, three-dimensional gauge theory, and the Atiyah-Hitchin manifold

    NARCIS (Netherlands)

    Dorey, N.; Khoze, V.V.; Mattis, M.P.; Tong, D.; Vandoren, S.

    1997-01-01

    We investigate quantum effects on the Coulomb branch of three-dimensional N = 4 supersymmetric gauge theory with gauge group SU(2). We calculate perturbative and one-instanton contributions to the Wilsonian effective action using standard weakcoupling methods. Unlike the four-dimensional case,

  18. Path integral quantization in the temporal gauge

    International Nuclear Information System (INIS)

    Scholz, B.; Steiner, F.

    1983-06-01

    The quantization of non-Abelian gauge theories in the temporal gauge is studied within Feynman's path integral approach. The standard asymptotic boundary conditions are only imposed on the transverse gauge fields. The fictituous longitudinal gauge quanta are eliminated asymptotically by modified boundary conditions. This abolishes the residual time-independent gauge transformations and leads to a unique fixing of the temporal gauge. The resulting path integral for the generating functional respects automatically Gauss's law. The correct gauge field propagator is derived. It does not suffer from gauge singularities at n x k = 0 present in the usual treatment of axial gauges. The standard principal value prescription does not work. As a check, the Wilson loop in temporal gauge is calculated with the new propagator. To second order (and to all orders in the Abelian case) the result agrees with the one obtained in the Feynman and Coulomb gauge. (orig.)

  19. Conversed, gauge-covariant colour charge in Su(n)QCD

    International Nuclear Information System (INIS)

    Selikhov, A.V.

    1988-01-01

    The definition of the integral of the group tensor and the gauge-covariant differential with respect to a distant point are given in the work. A conserved covariant charge dependence on family of paths has been contracted with the help of these notions. It has been shown that the same family of paths fixes a gauge in which the covariant and noncovariant conserved currents coicide. The gauge is characterized by representation of the vector potential via field strength tensor. The possibility of connecting the choice of the family of paths with the measurement procedure is discussed. 13 refs.; 2 figs

  20. Deconfinement on ℝ2×SL1×Sβ1 for all gauge groups and duality to double Coulomb gas

    International Nuclear Information System (INIS)

    Teeple, Brett

    2016-01-01

    I study finite-temperature N=1 super Yang-Mills for any gauge group G=A N ,B N ,C N ,D N ,E 6,7,8 ,F 4 ,G 2 , compactified from four dimensions on a torus, ℝ 2 ×S L 1 ×S β 1 . I examine in particular the low temperature regime L≪β=1/T, where L is the length of the spatial circle with periodic boundary conditions and with anti-periodic boundary conditions for the adjoint gauginos along the thermal cycle S β 1 . For small such L we are in a regime were semiclassical calculations can be performed and a transition occurs at T c much smaller than 1/NL. The transition is mediated by the competition between non-perturbative objects including ‘exotic’ topological molecules: neutral and magnetic bions composed of BPS and KK monopole constituents, with r=rank(G) different charges in the co-root lattice of the gauge group G, and the perturbative electrically charged W-bosons (along with their wino superpartners). The difference from non-SUSY theories here is that the Higgsing along the thermal cycle gives rise to a light modulus scalar field which couples to both bion-instantons and the W-bosons, and mediates a transition near T c where the bions and W-bosons compete with equal strengths. The transition is seen to be similar to previous studies on ℝ 3 ×S L 1 http://dx.doi.org/10.1007/JHEP11(2013)142; http://dx.doi.org/10.1007/JHEP09(2014)040; http://dx.doi.org/10.1007/JHEP03(2013)087; http://dx.doi.org/10.1007/JHEP09(2013)128 with general gauge group where a first order transition was found for all groups, but a second order one for the case of SU(2) on the torus ℝ 2 ×S L 1 ×S β 1 , which was subjected to lattice studies in http://dx.doi.org/10.1007/JHEP11(2013)142. I determine a duality to a double Coulomb gas of neutral and magnetic bions of different charges of their constituent monopole-instantons, and W-bosons of both scalar and electric charges. Aharanov-Bohm interactions exist between magnetic bions and W-bosons, and scalar charges of W-bosons and

  1. QCD and strongly coupled gauge theories: challenges and perspectives

    NARCIS (Netherlands)

    Brambilla, N.; Eidelman, S.; Foka, P.; Gardner, S.; Kronfeld, A. S.; Alford, M. G.; Alkofer, R.; Butenschoen, M.; Cohen, T. D.; Erdmenger, J.; Fabbietti, L.; Faber, M.; Goity, J. L.; Ketzer, B.; Lin, H. W.; Llanes-Estrada, F. J.; Meyer, H.; Pakhlov, P.; Pallante, E.; Polikarpov, M. I.; Sazdjian, H.; Schmitt, A.; Snow, W. M.; Vairo, A.; Vogt, R.; Vuorinen, A.; Wittig, H.; Arnold, P.; Christakoglou, P.; Nezza, P. Di; Fodor, Z.; Tormo, X. Garcia i; Höllwieser, R.; Kalwait, A.; Keane, D.; Kiritsis, E.; Mischke, A.; Mizuk, R.; Odyniec, G.; Papadodimas, K.; Pich, A.; Pittau, R.; Qiu, Jian-Wei; Ricciardi, G.; Salgado, C. A.; Schwenzer, K.; Stefanis, N. G.; Hippel, G. M. von; Zakharov, V. I .

    2014-01-01

    We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly-coupled, complex

  2. High energy behaviour of nonabelian gauge theories

    International Nuclear Information System (INIS)

    Bartels, J.

    1979-10-01

    The high energy behavior (in the Regge limit) of nonabelian gauge theories is reviewed. After a general remark concerning the question to what extent the Regge limit can be approached within perturbation theory, we first review the reggeization of elementary particles within nonabelian gauge theories. Then the derivation of a unitary high energy description of a massive (= spontaneously broken) nonabelian gauge model is described, which results in a complete reggeon calculus. There is strong evidence that the zero mass limit of this reggeon calculus exists, thus giving rise to the hope that the Regge behavior in pure Yang-Mills theories (QCD) can be reached in this way. In the final part of these lectures two possible strategies for solving this reggeon calculus (both for the massive and the massless case) are outlined. One of them leads to a geometrical picture in which the distribution of the wee partons obeys a diffusion law. The other one makes contact with reggeon field theory and predicts that QCD in the high energy limit is described by critical reggeon field theory. (orig.)

  3. Comparative Study of Algorithms for the Numerical Simulation of Lattice QCD

    International Nuclear Information System (INIS)

    Luz, Fernando H. P.; Mendes, Tereza

    2010-01-01

    Large-scale numerical simulations are the prime method for a nonperturbative study of QCD from first principles. Although the lattice simulation of the pure-gauge (or quenched-QCD) case may be performed very efficiently on parallel machines, there are several additional difficulties in the simulation of the full-QCD case, i.e. when dynamical quark effects are taken into account. We discuss the main aspects of full-QCD simulations, describing the most common algorithms. We present a comparative analysis of performance for two versions of the hybrid Monte Carlo method (the so-called R and RHMC algorithms), as provided in the MILC software package. We consider two degenerate flavors of light quarks in the staggered formulation, having in mind the case of finite-temperature QCD.

  4. Renormalization scheme and gauge (in)dependence of the generalized Crewther relation: what are the real grounds of the β-factorization property?

    Science.gov (United States)

    Garkusha, A. V.; Kataev, A. L.; Molokoedov, V. S.

    2018-02-01

    The problem of scheme and gauge dependence of the factorization property of the renormalization group β-function in the SU( N c ) QCD generalized Crewther relation (GCR), which connects the flavor non-singlet contributions to the Adler and Bjorken polarized sum rule functions, is investigated at the O({a}_s^4) level of perturbation theory. It is known that in the gauge-invariant renormalization \\overline{MS} -scheme this property holds in the QCD GCR at least at this order. To study whether this factorization property is true in all gauge-invariant schemes, we consider the MS-like schemes in QCD and the QED-limit of the GCR in the \\overline{MS} -scheme and in two other gauge-independent subtraction schemes, namely in the momentum MOM and the on-shell OS schemes. In these schemes we confirm the existence of the β-function factorization in the QCD and QED variants of the GCR. The problem of the possible β-factorization in the gauge-dependent renormalization schemes in QCD is studied. To investigate this problem we consider the gauge non-invariant mMOM and MOMgggg-schemes. We demonstrate that in the mMOM scheme at the O({a}_s^3) level the β-factorization is valid for three values of the gauge parameter ξ only, namely for ξ = -3 , -1 and ξ = 0. In the O({a}_s^4) order of PT it remains valid only for case of the Landau gauge ξ = 0. The consideration of these two gauge-dependent schemes for the QCD GCR allows us to conclude that the factorization of RG β-function will always be implemented in any MOM-like renormalization schemes with linear covariant gauge at ξ = 0 and ξ = -3 at the O({a}_s^3) approximation. It is demonstrated that if factorization property for the MS-like schemes is true in all orders of PT, as theoretically indicated in the several works on the subject, then the factorization will also occur in the arbitrary MOM-like scheme in the Landau gauge in all orders of perturbation theory as well.

  5. Constituent gluons and the static quark potential

    Energy Technology Data Exchange (ETDEWEB)

    Greensite, Jeff [San Francisco State Univ., CA (United States); Szczepaniak, Adam P. [Indiana Univ., Bloomington, IN (United States); Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)

    2016-04-01

    We suggest that Hamiltonian matrix elements between physical states in QCD might be approximated, in Coulomb gauge, by "lattice-improved" tree diagrams; i.e. tree diagram contributions with dressed ghost, transverse gluon, and Coulomb propagators obtained from lattice simulations. Such matrix elements can be applied to a variational treatment of hadronic states which include constituent gluons. As an illustration and first application of this hybrid approach, we derive a variational estimate of the heavy quark potential for distances up to 2.5 fm. The Coulomb string tension in SU(3) gauge theory is about a factor of four times greater than the asymptotic string tension. In our variational approach, using for simplicity a single variational parameter, we can reduce this overshoot by nearly the factor required. The building blocks of our approach are Coulomb gauge propagators, and in this connection we present new lattice results for the ghost and transverse gluon propagators in position space.

  6. Proceedings, QCD-TNT-III, From Quarks and Gluons to Hadronic Matter: A Bridge too Far?

    CERN Document Server

    2013-01-01

    In the third edition of the QCD-TNT workshop the traditional focus of the last two editions (that is gaining a firmer grasp on the infrared behavior of the QCD Green's functions) will be slightly shifted towards attempts to implement the transition from the fundamental (quarks and gluons) to the effective (mesons and hadrons) degrees of freedom. So in addition to the traditional QCD-TNT themes (e.g., confinement, gluon mass generation, lattice simulations in different gauges, QCD at finite temperature and density) we plan to have more phenomenologically oriented topics (e.g., experimental reviews, determination of form factors from first principle, construction of Bethe-Salpeter kernels). In addition, a special session will be dedicated to review talks, summarizing the state-of-the-art, as well as highlighting the future perspectives, of simulating non-Abelian gauge fields using ultracold neutral atoms trapped in optical lattices, and other systems.

  7. Polarization asymmetries and gauge theory interactions at short distances

    International Nuclear Information System (INIS)

    Craigie, N.S.

    1983-01-01

    In this talk, we give the arguments as to why spin asymmetries test fundamental properties of the underlying gauge theories of elementary particles, concentrating mainly on electro-weak and QCD interactions, but also looking at the future and possible signatures for supersymmetric strong interactions. We also mention briefly the role helicity asymmetry measurements can play as regards higher order corrections, including higher twist, in QCD. (orig./HSI)

  8. The Pomeron and hadrons through infra-red analysis of QCD

    International Nuclear Information System (INIS)

    White, A.R.

    1981-01-01

    Infra-red analysis of QCD in the Regge limit is argued to lead to confinement with chiral symmetry breaking. The resulting Pomeron depends strongly on the centre of the gauge group with SU(3) colour producing uniquely the experimentally observed even signature, factorizing, Pomeron. The critical Pomeron (asymptotic rising cross-sections) occurs when QCD is saturated with quarks. New calculations are reviewed showing strong evidence for the emergence of the critical Pomeron diffraction peak at present accelerator energies. This leads to exciting predictions for diffraction scattering at p antip collider energies which could become the most precise experimental confirmation of QCD

  9. Constructing a neutron star from the lattice in G{sub 2}-QCD

    Energy Technology Data Exchange (ETDEWEB)

    Hajizadeh, Ouraman; Maas, Axel [University of Graz, Institute of Physics, NAWI Graz (Austria)

    2017-10-15

    The inner structure of neutron stars is still an open question. One obstacle is the infamous sign problem of lattice QCD, which bars access to the high-density equation of state. A possibility to make progress and understand the qualitative impact of gauge interactions on the neutron star structure is to study a modified version of QCD without the sign problem. In the modification studied here the gauge group of QCD is replaced by the exceptional Lie group G{sub 2}, which keeps neutrons in the spectrum. Using an equation of state from lattice calculations only we determine the mass-radius-relation for a neutron star using the Tolman-Oppenheimer-Volkoff equation. This allows us to understand the challenges and approximations currently necessary to use lattice data for this purpose. We discuss in detail the particular uncertainties and systematic problems of this approach. (orig.)

  10. QCD, unification and the road to asymptopia

    International Nuclear Information System (INIS)

    Lindenbaum, S.J.

    1980-11-01

    Attempts to describe interactions at extremely high energies are addressed. Previous beliefs that asymptopia - the theoretically promised land where all asymptotic theorems come true - was reached have always proven false. Present estimates of asymptopia range from 10 5 GeV to 10 16 GeV. In the author's opinion it is premature to believe that the universe is described by a hierarchy of nested gauge groups. The establishment of QCD as the nonabelian gauge group describing strong interactions has not yet been accomplished. 2 figures

  11. Quasiparticles in QCD thermodynamics and applications

    International Nuclear Information System (INIS)

    Schneider, R.A.; Renk, T.

    2002-01-01

    We propose a novel quasiparticle interpretation of the equation of state of deconfined QCD at finite temperature. Using appropriate thermal masses, we introduce a phenomenological parametrization of the onset of confinement in the vicinity of the phase transition. Lattice results of the energy density, the pressure and the interaction measure of pure SU(3) gauge theory are well reproduced. A relation between the thermal energy density of the Yang-Mills vacuum and the chromomagnetic condensate left angle B 2 right angle T is found. We also present the two flavour QCD equation of state for realistic quark masses and apply the model to dilepton production in ultrarelativistic heavy-ion collisions. (orig.)

  12. Miracles in Scattering Amplitudes: from QCD to Gravity

    Energy Technology Data Exchange (ETDEWEB)

    Volovich, Anastasia [Brown Univ., Providence, RI (United States)

    2016-10-09

    The goal of my research project "Miracles in Scattering Amplitudes: from QCD to Gravity" involves deepening our understanding of gauge and gravity theories by exploring hidden structures in scattering amplitudes and using these rich structures as much as possible to aid practical calculations.

  13. Holographic models and the QCD trace anomaly

    International Nuclear Information System (INIS)

    Goity, Jose L.; Trinchero, Roberto C.

    2012-01-01

    Five dimensional dilaton models are considered as possible holographic duals of the pure gauge QCD vacuum. In the framework of these models, the QCD trace anomaly equation is considered. Each quantity appearing in that equation is computed by holographic means. Two exact solutions for different dilaton potentials corresponding to perturbative and non-perturbative β-functions are studied. It is shown that in the perturbative case, where the β-function is the QCD one at leading order, the resulting space is not asymptotically AdS. In the non-perturbative case, the model considered presents confinement of static quarks and leads to a non-vanishing gluon condensate, although it does not correspond to an asymptotically free theory. In both cases analyses based on the trace anomaly and on Wilson loops are carried out.

  14. Motivations for AdS/QCD from 10D supergravity solutions

    International Nuclear Information System (INIS)

    De Paula, Wayne

    2016-01-01

    We discuss some attempts for the construction of gravity duals of QCD-like theories. It is analysed some properties of solutions of 10D Type IIB supergravity theory that attempt to be dual to N= 1 gauge theories, in particular the solutions that belong to Papadoulos-Tseytlin ansatz. We argue that one could obtain 5D effective theories from 10d solutions and it motivates the use of phenomenological AdS/QCD models. (paper)

  15. Playing with QCD I: effective field theories

    International Nuclear Information System (INIS)

    Fraga, Eduardo S.

    2009-01-01

    The building blocks of hadrons are quarks and gluons, although color is confined into singlet states. QCD is believed to be the fundamental theory of strong interactions. Its asymptotically free nature puts the vacuum out of reach for perturbation theory. The Lagrangian of QCD and the Feynman rules associated were built by using the Gauge Principle, starting from the quark matter fields and obtaining gluons as connections. A simpler, and sometimes necessary or complementary, approach is provided by effective field theories or effective models, especially when one has to deal with the nonperturbative sector of the theory. (author)

  16. Light-cone quantized QCD and novel hadron phenomenology

    International Nuclear Information System (INIS)

    Brodsky, S.J.

    1997-09-01

    The authors reviews progress made in solving gauge theories such as collinear quantum chromodynamics using light-cone Hamiltonian methods. He also shows how the light-cone Fock expansion for hadron wavefunctions can be used to compute operator matrix elements such as decay amplitudes, form factors, distribution amplitudes, and structure functions, and how it provides a tool for exploring novel features of QCD. The author also reviews commensurate scale relations, leading-twist identities which relate physical observables to each other, thus eliminating renormalization scale and scheme ambiguities in perturbative QCD predictions

  17. Electric Dipole Moment Results from lattice QCD

    Science.gov (United States)

    Dragos, Jack; Luu, Thomas; Shindler, Andrea; de Vries, Jordy

    2018-03-01

    We utilize the gradient flow to define and calculate electric dipole moments induced by the strong QCD θ-term and the dimension-6 Weinberg operator. The gradient flow is a promising tool to simplify the renormalization pattern of local operators. The results of the nucleon electric dipole moments are calculated on PACS-CS gauge fields (available from the ILDG) using Nf = 2+1, of discrete size 323×64 and spacing a ≃ 0.09 fm. These gauge fields use a renormalization-group improved gauge action and a nonperturbatively O(a) improved clover quark action at β = 1.90, with cSW = 1.715. The calculation is performed at pion masses of mπ ≃ 411, 701 MeV.

  18. Asymptotic states and infrared divergences in gauge theories

    International Nuclear Information System (INIS)

    Butler, D.R.

    1981-01-01

    The gauge theories, Gravity and QCD are shown to be infrared finite to a non-trival order by a generalization of the coherent state approach. The asymptotic Hamiltonian operator is used, along with a mathematical theorem by Magnus, to specify a S-operator and to show cancellation of infrared divergences at the amplitude level. This procedure is exemplified in Gravity to third order and applied to QCD for leading order divergences to fifth order in the coupling constant. Dimensional regularization is used to isolate the infrared singularities in QCD. The sections on Gravity include a derivation of the infrared structure of the propagators for a massive particle and the graviton

  19. Gauge equivalence of the electrodynamics of charged bosons

    International Nuclear Information System (INIS)

    Sohn, R.; Haller, K.

    1977-01-01

    The quantum electrodynamics of charged scalar and vector bosons is formulated in the Lorentz gauge, and the effect of the charged particle--photon interaction on the subsidiary condition is explicitly taken into account. The results are extensions of earlier work on spinor quantum electrodynamics, but the presence of seagull vertices and anomalous current commutators in the case of the charged bosons make the extensions nontrivial. An operator gauge transformation that encompasses equations of motion as well as the commutator algebra of the field operators is developed; it is used to transform the theory from the Lorentz gauge to the Coulomb gauge

  20. Effective actions for gauge theories with Chern-Simons terms - I

    International Nuclear Information System (INIS)

    Bambah, B.A.; Mukku, C.

    1989-01-01

    The effective Lagrangian for a three-dimensional gauge theory with a Chern-Simons term is evaluated upto one-loop effects. It is shown to be completely finite. It also does not exhibit any imaginary part. The calculation is carried out in a background field analogue of the Feynman gauge and gauge invariance is maintained throughout the calculation. In an appendix an argument is presented as to why this Feynman gauge may be a 'good' gauge for our results to be applied to high temperature QCD and in particular to the quark-gluon plasma. (author). 12 refs

  1. QCD, unification and the road to asymptopia

    Energy Technology Data Exchange (ETDEWEB)

    Lindenbaum, S.J.

    1980-11-01

    Attempts to describe interactions at extremely high energies are addressed. Previous beliefs that asymptopia - the theoretically promised land where all asymptotic theorems come true - was reached have always proven false. Present estimates of asymptopia range from 10/sup 5/ GeV to 10/sup 16/ GeV. In the author's opinion it is premature to believe that the universe is described by a hierarchy of nested gauge groups. The establishment of QCD as the nonabelian gauge group describing strong interactions has not yet been accomplished. 2 figures. (RWR)

  2. Decay constants in soft wall AdS/QCD revisited

    Energy Technology Data Exchange (ETDEWEB)

    Braga, Nelson R.F., E-mail: braga@if.ufrj.br [Instituto de Física, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, RJ 21941-972 (Brazil); Diles, Saulo, E-mail: smdiles@if.ufrj.br [Instituto de Física, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, RJ 21941-972 (Brazil); Contreras, M.A. Martin, E-mail: ma.martin41@uniandes.edu.co [High Energy Group, Department of Physics, Universidad de los Andes, Carrera 1, No 18A-10, Bloque Ip, ZIP 111711, Bogotá (Colombia)

    2016-12-10

    Phenomenological AdS/QCD models, like hard wall and soft wall, provide hadronic mass spectra in reasonable consistency with experimental and (or) lattice results. These simple models are inspired in the AdS/CFT correspondence and assume that gauge/gravity duality holds in a scenario where conformal invariance is broken through the introduction of an energy scale. Another important property of hadrons: the decay constant, can also be obtained from these models. However, a consistent formulation of an AdS/QCD model that reproduces the observed behavior of decay constants of vector meson excited states is still lacking. In particular: for radially excited states of heavy vector mesons, the experimental data lead to decay constants that decrease with the radial excitation level. We show here that a modified framework of soft wall AdS/QCD involving an additional dimensionfull parameter, associated with an ultraviolet energy scale, provides decay constants decreasing with radial excitation level. In this version of the soft wall model the two point function of gauge theory operators is calculated at a finite position of the anti-de Sitter space radial coordinate.

  3. Analytic stochastic regularization in QCD and its supersymmetric extension

    International Nuclear Information System (INIS)

    Abdalla, E.; Vianna, R.L.

    1987-08-01

    We outline some features of stochastic quantization and regularization of fermionic fields with applications to spinor QCD, showing the appearence of a non-gauge invariant counterterm. We also show that non-invariant terms cancel in supersymmetric multiplets. (Author) [pt

  4. A gauge invariant theory for time dependent heat current

    International Nuclear Information System (INIS)

    Chen, Jian; ShangGuan, Minhui; Wang, Jian

    2015-01-01

    In this work, we develop a general gauge-invariant theory for AC heat current through multi-probe systems. Using the non-equilibrium Green’s function, a general expression for time-dependent electrothermal admittance is obtained where we include the internal potential due to the Coulomb interaction explicitly. We show that the gauge-invariant condition is satisfied for heat current if the self-consistent Coulomb interaction is considered. It is known that the Onsager relation holds for dynamic charge conductance. We show in this work that the Onsager relation for electrothermal admittance is violated, except for a special case of a quantum dot system with a single energy level. We apply our theory to a nano capacitor where the Coulomb interaction plays an essential role. We find that, to the first order in frequency, the heat current is related to the electrochemical capacitance as well as the phase accumulated in the scattering event. (paper)

  5. TDA and RPA pseudoscalar and vector solutions for the low energy regime of a motivated QCD Hamiltonian.

    Science.gov (United States)

    Yépez-Martínez, T.; Amor Quiroz, D. A.; Hess, P. O.; Civitarese, O.

    2017-07-01

    We present the low energy meson spectrum of a Coulomb gauge QCD motivated Hamiltonian for light and strange quarks. We have used the harmonic oscillator as a trial basis and performed a pre-diagonalization of the kinetic energy term in order to get an effective basis where quark and anti-quark degrees of freedom are defined. For the relevant interactions between quarks and anti-quarks, we have implemented a confining interaction between color sources, in order to account in an effective way for the gluonic degrees of freedom. The low energy meson spectrum is obtained from the implementation of the TDA and RPA many-body-methods. The physical states have been described as TDA and RPA collective states with a relatively good agreement. Particularly, the particle-hole correlations of the RPA ground state improve the RPA pion-like state (159.7 MeV) close to its physical value while the TDA one remains at a higher energy (269.2 MeV).

  6. Bridging a gap between continuum-QCD and ab initio predictions of hadron observables

    Energy Technology Data Exchange (ETDEWEB)

    Binosi, Daniele [European Centre for Theoretical Studies in Nuclear Physics and Related Areas - ECT* and Fondazione Bruno Kessler, Villa Tambosi, Strada delle Tabarelle 286, I-38123 Villazzano (Italy); Chang, Lei [CSSM, School of Chemistry and Physics, University of Adelaide, Adelaide, SA 5005 (Australia); Papavassiliou, Joannis [Department of Theoretical Physics and IFIC, University of Valencia and CSIC, E-46100, Valencia (Spain); Roberts, Craig D., E-mail: cdroberts@anl.gov [Physics Division, Argonne National Laboratory, Argonne, IL 60439 (United States)

    2015-03-06

    Within contemporary hadron physics there are two common methods for determining the momentum-dependence of the interaction between quarks: the top-down approach, which works toward an ab initio computation of the interaction via direct analysis of the gauge-sector gap equations; and the bottom-up scheme, which aims to infer the interaction by fitting data within a well-defined truncation of those equations in the matter sector that are relevant to bound-state properties. We unite these two approaches by demonstrating that the renormalisation-group-invariant running-interaction predicted by contemporary analyses of QCD's gauge sector coincides with that required in order to describe ground-state hadron observables using a nonperturbative truncation of QCD's Dyson–Schwinger equations in the matter sector. This bridges a gap that had lain between nonperturbative continuum-QCD and the ab initio prediction of bound-state properties.

  7. Charmonium meson and hybrid radiative transitions

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Peng [Indiana U., JLAB; Yépez-Martínez, Tochtli [Indiana U.; Szczepaniak, Adam P. [Indiana U., JLAB

    2014-06-01

    We consider the non-relativistic limit of the QCD Hamiltonian in the Coulomb gauge, to describe radiative transitions between conventional charmonium states and from the lowest multiplet of cc¯ hybrids to charmonium mesons. The results are compared to potential quark models and lattices calculations.

  8. National Computational Infrastructure for Lattice Gauge Theory: Final report

    International Nuclear Information System (INIS)

    Reed, Daniel A.

    2008-01-01

    In this document we describe work done under the SciDAC-1 Project National Computerational Infrastructure for Lattice Gauge Theory. The objective of this project was to construct the computational infrastructure needed to study quantum chromodynamics (QCD). Nearly all high energy and nuclear physicists in the United States working on the numerical study of QCD are involved in the project, as are Brookhaven National Laboratory (BNL), Fermi National Accelerator Laboratory (FNAL), and Thomas Jefferson National Accelerator Facility (JLab). A list of the senior participants is given in Appendix A.2. The project includes the development of community software for the effective use of the terascale computers, and the research and development of commodity clusters optimized for the study of QCD. The software developed as part of this effort is publicly available, and is being widely used by physicists in the United States and abroad. The prototype clusters built with SciDAC-1 fund have been used to test the software, and are available to lattice gauge theorists in the United States on a peer reviewed basis

  9. Soft gluon resummation formulae for hard proton processes in QCD

    International Nuclear Information System (INIS)

    Craigie, N.S.; Jones, H.F.

    1980-01-01

    We briefly review the treatment of leading logarithmic behaviour of the parton distributions in QCD within the Bethe-Salpeter framework by analysing directly parton hadron Green functions in the limit of parton four-momentum k 2 → - infinitely in a special light-like gauge involving a spectator vector. This technique allows us to derive the factorization of parton probabilities in leading logarithmic order in QCD in the various inclusive processes involving a single short-distance scale. The proof requires us to show that the use of planar gauges eta = psub(A) + psub(B) + ..., where psub(A), psub(B)... are the observed hadron momenta, reduces to choosing the appropriate light-like gauge for each hadron-parton BS channel, after demonstrating a Bloch-Nordsieck cancellation of the real and virtual soft left-over gluons. In the case where two large momentum scales appear, by restricting the transverse phase space into which the gluons are radiated, we derive the double logarithmic eikonal renormalization of the hard scattering formula of the type proposed recently by Parisi and Petronzio. (orig.)

  10. Maximal Abelian and Curci-Ferrari gauges in momentum subtraction at three loops

    Science.gov (United States)

    Bell, J. M.; Gracey, J. A.

    2015-12-01

    The vertex structure of QCD fixed in the maximal Abelian gauge (MAG) and Curci-Ferrari gauge is analyzed at two loops at the fully symmetric point for the 3-point functions corresponding to the three momentum subtraction (MOM) renormalization schemes. Consequently, the three-loop renormalization group functions are determined for each of these three schemes in each gauge using properties of the renormalization group equation.

  11. The QCD Teraflops Project

    International Nuclear Information System (INIS)

    Gottlieb, S.

    1992-01-01

    Increased computer power is essential for future progress in lattice gauge theory and for other Grand challenge applications. We address the physics that can be done with a computer capable of sustaining 1 Teraflops for QCD and the technology that will make it possible to construct such a computer within the next three years. Our collaboration has proposed to build a computer based on the Thinking Machines CM5 communication network, but with nodes 10 times faster

  12. Building up the standard gauge model of high energy physics. 11

    International Nuclear Information System (INIS)

    Rajasekaran, G.

    1989-01-01

    This chapter carefully builds up, step by step, the standard gauge model of particle physics based on the group SU(3) c x SU(2) x U(1). Spontaneous symmetry breaking via the Nambu-Goldstone mode, and then via the Higgs mode for gauge theories, are presented via examples, first for the Abelian U(1) and then for the non-Abelian SU(2) case. The physically interesting SU(2) x U(1) model is then taken up. The emergence of massive vector bosons is demonstrated. After this preparation, the 'standard model' of the late 60's prior to the gauge theory revolution, based on the V-A current-current weak interactions, minimal electromagnetism, and an unspecified strong interaction, all in quark-lepton language, is set up. It is then compared to the standard gauge model of SU(3) c x SU(2) x U(1). The compelling reasons for QCD as the gauge theory of strong interactions are spelt out. An introduction to renormalization group methods as the main calculational tool for QCD, asymptotic freedom, infrared problems, and physically motivated reasons for going beyond the standard model are presented. (author). 6 refs.; 19 figs.; 2 tabs

  13. Hadronization of QCD and effective interactions

    International Nuclear Information System (INIS)

    Frank, M.R.

    1994-01-01

    An introductory treatment of hadronization through functional integral calculus and bifocal Bose fields is given. Emphasis is placed on the utility of this approach for providing a connection between QCD and effective hadronic field theories. The hadronic interactions obtained by this method are nonlocal due to the QCD substructure, yet, in the presence of an electromagnetic field, maintain the electromagnetic gauge invariance manifest at the quark level. A local chiral model which is structurally consistent with chiral perturbation theory is obtained through a derivative expansion of the nonlocalities with determined, finite coefficients. Tree-level calculations of the pion form factor and π - π scattering, which illustrate the dual constituent-quark-chiral-model nature of this approach, are presented

  14. Canonical ward identities in generalized QCD

    International Nuclear Information System (INIS)

    Li Ziping

    1995-01-01

    The canonical Ward identities for a system with singular higher-order Lagrangian are derived and some application to the generalized QCD are given. The new relations of the Ward identities for gauge ghost field proper vertices are obtained which differ from the usual Ward-Takahashi identities arising from BRS invariance. The expressions for PCAC and generalized PCAC of AVV vertices are also obtained

  15. Perspectives and Challenges for QCD Phenomenology

    International Nuclear Information System (INIS)

    Brodsky, Stanley J.

    2001-01-01

    A fundamental understanding of quantum chromodynamics, particularly at the amplitude level, is essential for progress in high energy physics. For example, the measurement and interpretation of the basic parameters of the electroweak theory and CP violation depends on an understanding of the dynamics and phase structure of exclusive B-meson decay amplitudes. In this review, I discuss a number of ways in which the required hadron wavefunctions can be measured (such as two-photon reactions and diffractive dissociation) or calculated from first principles. An important tool for describing relativistic composite systems in quantum field theory is the light-front Fock expansion, which encodes the properties of a hadrons in terms of a set of frame-independent n-particle wavefunctions. Light-front quantization in the doubly-transverse light-cone gauge has a number of remarkable advantages, including explicit unitarity, the absence of ghost degrees of freedom, and the decoupling properties needed to prove factorization theorems in high momentum transfer inclusive and exclusive reactions. Evolution in light-cone time allows the construction of an ''event amplitude generator'' in which only non-ghost physical degrees of freedom and integration over physical phase appear. The diffractive dissociation of a hadron at high energies, by either Coulomb or Pomeron exchange, has a natural description in QCD as the materialization of the projectile's light-cone wavefunctions; in particular, the diffractive dissociation of a meson, baryon, or photon into high transverse momentum jets measures the shape and other features of the projectile's distribution amplitude. Diffractive dissociation can thus test fundamental properties of QCD, including color transparency and intrinsic charm. I also review recent work which shows that the structure functions measured in deep inelastic lepton scattering are affected by final-state rescattering, thus modifying their connection with the light

  16. A problem of the QCD axion in supergravity

    International Nuclear Information System (INIS)

    Endo, M.; Takahashi, F.; Tokyo Univ.; Yanagida, T.T.; Tokyo Univ.

    2007-12-01

    We point out that the QCD axion generally couples to all the gauge fields in nature through the Super-Weyl, Kaehler and sigma-model anomalies in supergravity. If supersymmetry is dynamically broken by the hidden-sector gauge interactions, the axion potential receives corrections due to the instanton in the hidden sector. We show that the supersymmetry breaking models are tightly constrained for the Peccei-Quinn mechanism to successfully solve the strong CP problem. In particular, the gravity mediation turns out to be strongly disfavored. (orig.)

  17. Gauge theories in particle physics

    International Nuclear Information System (INIS)

    Aitchison, I.J.R.; Hey, A.J.G.

    1982-01-01

    The first theory, quantum electrodynamics (QED) is known to give a successful account of electromagnetic interactions. Weak and strong interactions are described by gauge theories which are generalisations of QED. The electro-weak gauge theory of Glashow Salam and Weinberg unites electromagnetic and weak interactions. Quantum chromodynamics (QCD) is the gauge theory of strong interactions. This approach to these theories, designed for the non-specialist, is based on a straightforward generalisation of non-relativistic quantum-mechanical perturbation theory to the relativistic case, leading to an intuitive introduction to Feynman graphs. Spontaneously broken-or 'hidden'-symmetries are given particular attention, with the physics of hidden gauge invariance and the role of the vacuum (essential to the unified theories) being illustrated by an extended but elementary discussion of the non-relativistic example of superconductivity. Throughout, emphasis is placed both on realistic calculations and on physical understanding. (author)

  18. Higgs phase in non-Abelian gauge theories

    International Nuclear Information System (INIS)

    Kaymakcalan, O.S.

    1981-06-01

    A non-Abelian gauge theory involving scalar fields with non-tachyonic mass terms in the Lagrangian is considered, in order to construct a finite energy density trial vacuum for this theory. The usual scalar potential arguments suggest that the vacuum of such a theory would be in the perturbative phase. However, the obvious choices for a vacuum in this phase, the Axial gauge and the Coulomb gauge bare vacua, do not have finite energy densities even with an ultraviolet cutoff. Indeed, it is a non-trivial problem to construct finite energy density vacua for non-Abelian gauge theories and this is intimately connected with the gauge fixing degeneracies of these theories. Since the gauge fixing is achieved in the Unitary gauge, this suggests that the Unitary gauge bare vacuum might be a finite energy trial vacuum and, despite the form of the scalar potential, the vacuum of this theory might be in a Higgs phase rather than the perturbative phase

  19. On the thermal phase structure of QCD at vanishing chemical potentials

    CERN Document Server

    Kabana, S

    2011-01-01

    The hypothesis is investigated, that the thermal structure of QCD phases at and near zero chemical potentials is determined by long range coherence, inducing the gauge boson pair condensate. The latter reflects the dynamical nature of gauge boson Bogoliubov transformations at the origin of localization of all color fields inside hadrons at low temperature in contrast to loss of such localization above a unique critical temperature.

  20. Electric Dipole Moment Results from lattice QCD

    Directory of Open Access Journals (Sweden)

    Dragos Jack

    2018-01-01

    Full Text Available We utilize the gradient flow to define and calculate electric dipole moments induced by the strong QCD θ-term and the dimension-6 Weinberg operator. The gradient flow is a promising tool to simplify the renormalization pattern of local operators. The results of the nucleon electric dipole moments are calculated on PACS-CS gauge fields (available from the ILDG using Nf = 2+1, of discrete size 323×64 and spacing a ≃ 0.09 fm. These gauge fields use a renormalization-group improved gauge action and a nonperturbatively O(a improved clover quark action at β = 1.90, with cSW = 1.715. The calculation is performed at pion masses of mπ ≃ 411, 701 MeV.

  1. Gauge invariance properties and singularity cancellations in a modified PQCD

    CERN Document Server

    Cabo-Montes de Oca, Alejandro; Cabo, Alejandro; Rigol, Marcos

    2006-01-01

    The gauge-invariance properties and singularity elimination of the modified perturbation theory for QCD introduced in previous works, are investigated. The construction of the modified free propagators is generalized to include the dependence on the gauge parameter $\\alpha $. Further, a functional proof of the independence of the theory under the changes of the quantum and classical gauges is given. The singularities appearing in the perturbative expansion are eliminated by properly combining dimensional regularization with the Nakanishi infrared regularization for the invariant functions in the operator quantization of the $\\alpha$-dependent gauge theory. First-order evaluations of various quantities are presented, illustrating the gauge invariance-properties.

  2. RIKEN BNL RESEARCH CENTER WORKSHOP ON GAUGE-INVARIANT VARIABLES IN GAUGE THEORIES, VOLUME 20

    Energy Technology Data Exchange (ETDEWEB)

    VAN BAAL,P.; ORLAND,P.; PISARSKI,R.

    2000-06-01

    This four-day workshop focused on the wide variety of approaches to the non-perturbative physics of QCD. The main topic was the formulation of non-Abelian gauge theory in orbit space, but some other ideas were discussed, in particular the possible extension of the Maldacena conjecture to nonsupersymmetric gauge theories. The idea was to involve most of the participants in general discussions on the problem. Panel discussions were organized to further encourage debate and understanding. Most of the talks roughly fell into three categories: (1) Variational methods in field theory; (2) Anti-de Sitter space ideas; (3) The fundamental domain, gauge fixing, Gribov copies and topological objects (both in the continuum and on a lattice). In particular some remarkable progress in three-dimensional gauge theories was presented, from the analytic side by V.P. Nair and mostly from the numerical side by O. Philipsen. This work may ultimately have important implications for RHIC experiments on the high-temperature quark-gluon plasma.

  3. QCD in the color-flow representation

    Energy Technology Data Exchange (ETDEWEB)

    Kilian, W. [Siegen Univ. (Germany). Fachbereich 7 - Physik; Ohl, T. [Wuerzburg Univ. (Germany). Inst. fuer Theoretische Physik und Astrophysik; Reuter, J. [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Speckner, C. [Freiburg Univ. (Germany). Physikalisches Inst.

    2012-06-15

    For many practical purposes, it is convenient to formulate unbroken nonabelian gauge theories like QCD in a color-flow basis. We present a new derivation of SU(N) interactions in the color-flow basis by extending the gauge group to U(N) x U(1)' in such a way that the two U(1) factors cancel each other. We use the quantum action principles to show the equivalence to the usual basis to all orders in perturbation theory. We extend the known Feynman rules to exotic color representations (e.g. sextets) and interactions (e.g. {epsilon}{sub ijk}). We discuss practical applications as they occur in automatic computation programs.

  4. QCD in the color-flow representation

    International Nuclear Information System (INIS)

    Kilian, W.; Speckner, C.

    2012-06-01

    For many practical purposes, it is convenient to formulate unbroken nonabelian gauge theories like QCD in a color-flow basis. We present a new derivation of SU(N) interactions in the color-flow basis by extending the gauge group to U(N) x U(1)' in such a way that the two U(1) factors cancel each other. We use the quantum action principles to show the equivalence to the usual basis to all orders in perturbation theory. We extend the known Feynman rules to exotic color representations (e.g. sextets) and interactions (e.g. ε ijk ). We discuss practical applications as they occur in automatic computation programs.

  5. Calculability of the n-p mass difference in gauge theories

    International Nuclear Information System (INIS)

    Kiskis, J.

    1980-01-01

    The requirement of a calculable n-p mass difference leads to a consideration of unified gauge theories. Future developments in grand unified models may provide a realistic framework for the calculation of the n-p mass difference. The possibility that the relatively soft ultraviolet behavior of QCD softens the divergence in the lowest-order electromagnetic mass shift is considered in detail. It is shown that, if the bare mass and QCD coupling are constrained to be independent of the electromagnetic coupling, as is natural, then the lowest-order electromagnetic shifts of the renormalized mass and QCD coupling are infinite

  6. MS-on-shell quark mass relation up to four loops in QCD and a general SU(N) gauge group

    International Nuclear Information System (INIS)

    Marquard, Peter; Smirnov, Alexander V.; Smirnov, Vladimir A.; Steinhauser, Matthias; Wellmann, David

    2016-06-01

    In this paper we compute the relation between heavy quark masses defined in the modified minimal subtraction and on-shell scheme. Detailed results are presented for all coefficients of the SU(N_c) colour factors. The reduction of the four-loop on-shell integrals is performed for a general QCD gauge parameter. Some of the about 380 master integrals are computed analytically, others with high numerical precision based on Mellin-Barnes representations, and the rest numerically with the help of FIESTA. We discuss in detail the precise numerical evaluation of the four-loop master integrals. Updated relations between various short-distance masses and the MS quark mass to next-to-next-to-next-to-leading order accuracy are provided for the charm, bottom and top quark. We discuss the dependence on the renormalization and factorization scale.

  7. Are the dressed gluon and ghost propagators in the Landau gauge presently determined in the confinement regime of QCD?

    International Nuclear Information System (INIS)

    Pennington, M. R.; Wilson, D. J.

    2011-01-01

    The gluon and ghost propagators in Landau gauge QCD are investigated using the Schwinger-Dyson equation approach. Working in Euclidean spacetime, we solve for these propagators using a selection of vertex inputs, initially for the ghost equation alone and then for both propagators simultaneously. The results are shown to be highly sensitive to the choices of vertices. We favor the infrared finite ghost solution from studying the ghost equation alone where we argue for a specific unique solution. In order to solve this simultaneously with the gluon using a dressed-one-loop truncation, we find that a nontrivial full ghost-gluon vertex is required in the vanishing gluon momentum limit. The self-consistent solutions we obtain correspond to having a masslike term in the gluon propagator dressing, in agreement with similar studies supporting the long-held proposal of Cornwall.

  8. Mixed colour states in QCD confining vacuum

    OpenAIRE

    Buividovich, P. V.; Kuvshinov, V. I.

    2005-01-01

    We show that confinement of spinless heavy quarks in fundamental representation of $SU(N_{c})$ gauge group can be treated as decoherence of pure colour state into a white mixture of states. Decoherence rate is found to be proportional to the tension of QCD string and the distance between colour charges. The purity of colour states is calculated.

  9. Gauge symmetry, chirality and parity effects in four-particle systems: Coulomb's law as a universal function for diatomic molecules.

    Science.gov (United States)

    Van Hooydonk, G

    2000-11-01

    Following recent work in search for a universal function (Van Hooydonk, Eur. J. Inorg. Chem., (1999), 1617), we test four symmetric +/- a(n)Rn potentials for reproducing molecular potential energy curves (PECs). Classical gauge symmetry for 1/R-potentials results in generic left right asymmetric PECs. A pair of symmetric perturbed Coulomb potentials is quantitatively in accordance with observed PECs. For a bond, a four-particle system, charge inversion (a parity effect, atom chirality) is the key to explain this shape generically. A parity adapted Hamiltonian reduces from ten to two terms and to a soluble Bohr-like formula, a Kratzer (1 - Re/R)2 potential. The result is similar to the combined action of spin and wave function symmetry upon the Hamiltonian in Heitler-London theory. Analytical perturbed Coulomb functions varying with (1 - Re/R) scale attractive and repulsive branches of PECs for 13 bonds H2, HF, LiH, KH, AuH, Li2, LiF, KLi, NaCs, Rb2, RbCs, Cs2 and I2 in a single straight line. The 400 turning points for 13 bonds are reproduced with a deviation of 0.007 A at both branches. For 230 points at the repulsive side, the deviation is 0.003 A. The perturbed electrostatic Coulomb law is a universal molecular function. Ab initio zero molecular parameter functions give PECs of acceptable quality, just using atomic ionisation energies. The function can be used as a model potential for inverting levels and gives a first principle's comparison of short- and long-range interactions, important for the study of cold atoms. Wave-packet dynamics, femto-chemistry applied to the crossing of covalent and ionic curves, can provide evidence for this theory. We anticipate this scale/shape invariant scheme applies to smaller scales in nuclear and high-energy particle physics. For larger gravitational scales (Newton 1/R potentials), problems with super-unification are discussed. Reactions between hydrogen and antihydrogen, feasible in the near future, will probably produce

  10. Partially quenched lattice QCD with two degenerate dynamical light Wilson quarks

    International Nuclear Information System (INIS)

    De, Asit K.; Harindranath, A.; Maiti, Jyotirmoy

    2006-01-01

    We present our results of numerical studies of partially quenched latticed QCD with two degenerate flavors of dynamical quarks. Gauge configurations are generated with Wilson gauge action and tadpole improved Wilson fermions at β = 5.6 and K sea = 0.155, 0.156, 0.157 and 0.158. Suitably smeared gauge configurations are used to calculate the static interquark potential in order to set the physical scale. Mesonic propagators are calculated at above mentioned four different values of K val for each K sea . We present results for pion and rho masses. (author)

  11. A new simulation algorithm for lattice QCD with dynamical quarks

    CERN Document Server

    Bunk, B.; Jegerlehner, B.; Luscher, M.; Simma, H.; Sommer, R.; Bunk, B; Jansen, K; Jegerlehner, B; Luscher, M; Simma, H

    1994-01-01

    A previously introduced multi-boson technique for the simulation of QCD with dynamical quarks is described and some results of first test runs on a 6^3\\times12 lattice with Wilson quarks and gauge group SU(2) are reported.

  12. QCD as a topologically ordered system

    International Nuclear Information System (INIS)

    Zhitnitsky, Ariel R.

    2013-01-01

    We argue that QCD belongs to a topologically ordered phase similar to many well-known condensed matter systems with a gap such as topological insulators or superconductors. Our arguments are based on an analysis of the so-called “deformed QCD” which is a weakly coupled gauge theory, but nevertheless preserves all the crucial elements of strongly interacting QCD, including confinement, nontrivial θ dependence, degeneracy of the topological sectors, etc. Specifically, we construct the so-called topological “BF” action which reproduces the well known infrared features of the theory such as non-dispersive contribution to the topological susceptibility which cannot be associated with any propagating degrees of freedom. Furthermore, we interpret the well known resolution of the celebrated U(1) A problem where the would be η ′ Goldstone boson generates its mass as a result of mixing of the Goldstone field with a topological auxiliary field characterizing the system. We then identify the non-propagating auxiliary topological field of the BF formulation in deformed QCD with the Veneziano ghost (which plays the crucial role in resolution of the U(1) A problem). Finally, we elaborate on relation between “string-net” condensation in topologically ordered condensed matter systems and long range coherent configurations, the “skeletons”, studied in QCD lattice simulations. -- Highlights: •QCD may belong to a topologically ordered phase similar to condensed matter (CM) systems. •We identify the non-propagating topological field in deformed QCD with the Veneziano ghost. •Relation between “string-net” condensates in CM systems and the “skeletons” in QCD lattice simulations is studied

  13. Electron-positron scattering and gauge theories

    International Nuclear Information System (INIS)

    Davier, M.

    1983-07-01

    Recent results from high-energy e + e - colliding facilities are reviewed in the context of gauge theories. First QCD analyses are discussed and difficulties are seen to arise from the interplay between perturbative QCD and non-perturbative fragmentation processes. Many results have been recently obtained on weak electromagnetic interference, strengthening our faith in the standard SU(2) x U(1) theory: however some pieces are still missing and looked for. Finally, vigourous searches are pursued to find clues for physics beyond the SU(3) x SU(2) x U(1) framework: among those supersymmetric particles are being actively hunted in a large variety of situations

  14. Lattice QCD for nuclear physics

    CERN Document Server

    Meyer, Harvey

    2015-01-01

    With ever increasing computational resources and improvements in algorithms, new opportunities are emerging for lattice gauge theory to address key questions in strongly interacting systems, such as nuclear matter. Calculations today use dynamical gauge-field ensembles with degenerate light up/down quarks and the strange quark and it is possible now to consider including charm-quark degrees of freedom in the QCD vacuum. Pion masses and other sources of systematic error, such as finite-volume and discretization effects, are beginning to be quantified systematically. Altogether, an era of precision calculation has begun, and many new observables will be calculated at the new computational facilities.  The aim of this set of lectures is to provide graduate students with a grounding in the application of lattice gauge theory methods to strongly interacting systems, and in particular to nuclear physics.  A wide variety of topics are covered, including continuum field theory, lattice discretizations, hadron spect...

  15. QCD factorization beyond leading twist in exclusive processes: rhoT-meson production

    International Nuclear Information System (INIS)

    Wallon, S.; Anikin, I.; ); Ivanov, D.; Pire, B.; Szymanowski, L.

    2009-01-01

    Exclusive processes in hard electroproduction with asymptotic γ * p center of mass energy is one of the best place for understanding QCD in the perturbative Regge limit. The HERA experiment recently provided precise data for rho electroproduction, including all spin density matrix elements. From QCD, it is expected that such a process should factorize between a hard (calculable) coefficient function, and hadronic (P and ρ) matrix elements. Such a factorization is up to now only proven for a longitudinally polarized rho. Within the kt-factorization approach (valid at large s γ * p), we evaluate the impact factor of the transition γ * → ρT taking into account the twist 3 contributions. We show that a gauge invariant expression is obtained with the help of QCD equations of motion. More generally, relying on these equations and on the gauge invariance of the factorized amplitude, the non-perturbative Distribution Amplitudes can be reduced to a minimal set. This opens the way to a consistent treatment of factorization for exclusive processes with a transversally polarized vector meson. (author)

  16. Gauge-invariant on-shell Z1 in QED and QCD

    International Nuclear Information System (INIS)

    Fleischer, J.; Tarasov, O.V.

    1992-01-01

    Results of the two-loop calculation of the renormalization constant Z 1 for the on-shell fermion-fermion-vector vertex function of a general gauge theory with one massive fermion and the other particles massless are presented. Computations were performed in n dimensions and for an arbitrary covariant gauge. We found Z 1 to be gauge invariant in a renormalization scheme with simultaneous dimensional regularization of ultraviolet and infrared divergences. The charge renormalization constant in this scheme has ultraviolet and infrared divergences. It is found that infrared divergent terms in one- and two-loop approximation are proportional to be appropriate coefficient of the β function determined by ultraviolet divergences of massless particles, i.e. gluons and massless fermions. (orig.)

  17. Nonperturbative QCD simulations with 2+1 flavors of improved staggered quarks

    International Nuclear Information System (INIS)

    Bazavov, A.; Toussaint, D.; Bernard, C.; Laiho, J.; DeTar, C.; Levkova, L.; Oktay, M. B.; Gottlieb, Steven; Heller, U. M.; Hetrick, J. E.; Mackenzie, P. B.; Sugar, R.; Van de Water, R. S.

    2010-01-01

    Dramatic progress has been made over the last decade in the numerical study of quantum chromodynamics (QCD) through the use of improved formulations of QCD on the lattice (improved actions), the development of new algorithms, and the rapid increase in computing power available to lattice gauge theorists. In this article simulations of full QCD are described using the improved staggered quark formalism, ''asqtad'' fermions. These simulations were carried out with two degenerate flavors of light quarks (up and down) and with one heavier flavor, the strange quark. Several light quark masses, down to about three times the physical light quark mass, and six lattice spacings have been used. These enable controlled continuum and chiral extrapolations of many low energy QCD observables. The improved staggered formalism is reviewed, emphasizing both advantages and drawbacks. In particular, the procedure for removing unwanted staggered species in the continuum limit is reviewed. Then the asqtad lattice ensembles created by the MILC Collaboration are described. All MILC lattice ensembles are publicly available, and they have been used extensively by a number of lattice gauge theory groups. The physics results obtained with them are reviewed, and the impact of these results on phenomenology is discussed. Topics include the heavy quark potential, spectrum of light hadrons, quark masses, decay constants of light and heavy-light pseudoscalar mesons, semileptonic form factors, nucleon structure, scattering lengths, and more.

  18. Diquark correlations in baryons on the lattice with overlap quarks

    Energy Technology Data Exchange (ETDEWEB)

    Babich, R.; Howard, J.; Rebbi, C. [Boston Univ., MA (United States). Dept. of Physics; Garron, N. [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany); Hoelbling, C. [Wuppertal Univ. (Gesamthochschule) (Germany). Fachbereich Physik; Lellouch, L. [CNRS Luminy, Marseille (France). Centre de Physique Theorique]|[Wuppertal Univ. (Gesamthochschule) (Germany). Fachbereich Physik

    2007-01-15

    We evaluate baryon wave functions in both the Coulomb and Landau gauge in lattice QCD. These are constructed from quark propagators calculated with the overlap Dirac operator on quenched gauge configurations at {beta}=6. By comparing baryon states that differ in their diquark content, we find evidence for enhanced correlation in the scalar diquark channel, as favored by quark models. We also summarize earlier results for diquark masses in the Landau gauge, casting them in a form more easily compared with subsequent studies. (orig.)

  19. Diquark correlations in baryons on the lattice with overlap quarks

    International Nuclear Information System (INIS)

    Babich, R.; Howard, J.; Rebbi, C.; Hoelbling, C.; Lellouch, L.; Wuppertal Univ.

    2007-01-01

    We evaluate baryon wave functions in both the Coulomb and Landau gauge in lattice QCD. These are constructed from quark propagators calculated with the overlap Dirac operator on quenched gauge configurations at β=6. By comparing baryon states that differ in their diquark content, we find evidence for enhanced correlation in the scalar diquark channel, as favored by quark models. We also summarize earlier results for diquark masses in the Landau gauge, casting them in a form more easily compared with subsequent studies. (orig.)

  20. Gauge-invariant screening masses and static quark free energies in Nf=2 +1 QCD at nonzero baryon density

    Science.gov (United States)

    Andreoli, Michele; Bonati, Claudio; D'Elia, Massimo; Mesiti, Michele; Negro, Francesco; Rucci, Andrea; Sanfilippo, Francesco

    2018-03-01

    We discuss the extension of gauge-invariant electric and magnetic screening masses in the quark-gluon plasma to the case of a finite baryon density, defining them in terms of a matrix of Polyakov loop correlators. We present lattice results for Nf=2 +1 QCD with physical quark masses, obtained using the imaginary chemical potential approach, which indicate that the screening masses increase as a function of μB. A separate analysis is carried out for the theoretically interesting case μB/T =3 i π , where charge conjugation is not explicitly broken and the usual definition of the screening masses can be used for temperatures below the Roberge-Weiss transition. Finally, we investigate the dependence of the static quark free energy on the baryon chemical potential, showing that it is a decreasing function of μB, which displays a peculiar behavior as the pseudocritical transition temperature at μB=0 is approached.

  1. Relativistic and Nuclear Medium Effects on the Coulomb Sum Rule.

    Science.gov (United States)

    Cloët, Ian C; Bentz, Wolfgang; Thomas, Anthony W

    2016-01-22

    In light of the forthcoming high precision quasielastic electron scattering data from Jefferson Lab, it is timely for the various approaches to nuclear structure to make robust predictions for the associated response functions. With this in mind, we focus here on the longitudinal response function and the corresponding Coulomb sum rule for isospin-symmetric nuclear matter at various baryon densities. Using a quantum field-theoretic quark-level approach which preserves the symmetries of quantum chromodynamics, as well as exhibiting dynamical chiral symmetry breaking and quark confinement, we find a dramatic quenching of the Coulomb sum rule for momentum transfers |q|≳0.5  GeV. The main driver of this effect lies in changes to the proton Dirac form factor induced by the nuclear medium. Such a dramatic quenching of the Coulomb sum rule was not seen in a recent quantum Monte Carlo calculation for carbon, suggesting that the Jefferson Lab data may well shed new light on the explicit role of QCD in nuclei.

  2. Lattice gauge theories

    International Nuclear Information System (INIS)

    Petronzio, R.

    1992-01-01

    Lattice gauge theories are about fifteen years old and I will report on the present status of the field without making the elementary introduction that can be found in the proceedings of the last two conferences. The talk covers briefly the following subjects: the determination of α s , the status of spectroscopy, heavy quark physics and in particular the calculation of their hadronic weak matrix elements, high temperature QCD, non perturbative Higgs bounds, chiral theories on the lattice and induced theories

  3. Factorization and pion form factor in QCD

    International Nuclear Information System (INIS)

    Efremov, A.V.; Radyushkin, A.V.

    1979-01-01

    The behaviour of the pion electromagnetic form factor (EMFF) in the framework of quantum chromodynamics (QCD) is discussed. Pion is considered to be a quark-antiquark bound state. It is proposed to use an OPE description of the bound state structure by matrix elements of certain local gauge-invariant operators. Short-distance quark interactions is proved using a direct analysis of perturbation theory in the α-parametric representation of the Feynman diagrams. It is shown that the short-distance parton picture privides a self-consistent description of the large Q 2 momentum behaviour of the pion EMFF in QCD. Pion EMFF asymptotics is expressed in terms of fu fundamental constants of the theory

  4. A transverse lattice QCD model for mesons

    Energy Technology Data Exchange (ETDEWEB)

    Patel, Apoorva D.; Ratabole, Raghunath

    2004-03-01

    QCD is analysed with two light-front continuum dimensions and two transverse lattice dimensions. In the limit of large number of colours and strong transverse gauge coupling, the contributions of light-front and transverse directions factorise in the dynamics, and the theory can be analytically solved in a closed form. An integral equation is obtained, describing the properties of mesons, which generalises the 't Hooft equation by including spin degrees of freedom. The meson spectrum, light-front wavefunctions and form factors can be obtained by solving this equation numerically. These results would be a good starting point to model QCD observables which only weakly depend on transverse directions, e.g. deep inelastic scattering structure functions.

  5. Relativistic Many-Body Hamiltonian Approach to Mesons

    OpenAIRE

    Llanes-Estrada, Felipe J.; Cotanch, Stephen R.

    2001-01-01

    We represent QCD at the hadronic scale by means of an effective Hamiltonian, $H$, formulated in the Coulomb gauge. As in the Nambu-Jona-Lasinio model, chiral symmetry is explicity broken, however our approach is renormalizable and also includes confinement through a linear potential with slope specified by lattice gauge theory. This interaction generates an infrared integrable singularity and we detail the computationally intensive procedure necessary for numerical solution. We focus upon app...

  6. Coulomb interaction from the interplay between confinement and screening

    International Nuclear Information System (INIS)

    Gaete, P.; Guendelman, E.I.

    2004-01-01

    It has been noticed that confinement effects can be described by the addition of a √(-F μν a F aμν ) term in the Lagrangian density. We now study the combined effect of such 'confinement term' and that of a mass term. The surprising result is that the interplay between these two terms gives rise to a Coulomb interaction. Our picture has a certain correspondence with the quasiconfinement picture described by Giles, Jaffe and de Rujula for QCD with symmetry breaking

  7. Topological and magnetic properties of the QCD vacuum probed by overlap fermions

    International Nuclear Information System (INIS)

    Braguta, V.V.; Buividovich, P.V.; Polikarpov, M.I.

    2013-02-01

    We study some of the local CP-odd and magnetic properties of the non-Abelian vacuum with use of overlap fermions within the quenched lattice gauge theory. Among these properties are the following: inhomogeneous spatial distribution of the topological charge density (chirality for massless fermions) in SU(2) gluodynamics (for uncooled gauge configurations the chirality is localized on low-dimensional defects with d=2.3, while a sequence of cooling steps gives rise to four-dimensional instantons and hence a four-dimensional structure of the chirality distribution); finite local fluctuations of the chirality growing with the strength of an external magnetic field; magnetization and susceptibility of the QCD vacuum in SU(3) theory; magnetic catalysis of the chiral symmetry breaking, and the electric conductivity of the QCD vacuum in strong magnetic fields.

  8. Topological and magnetic properties of the QCD vacuum probed by overlap fermions

    Energy Technology Data Exchange (ETDEWEB)

    Braguta, V.V. [Institut Fiziki Vysokikh Ehnergij, Protvino (Russian Federation); Institute of Theoretical and Experimental Physics, Moscow (Russian Federation); Buividovich, P.V. [Univ. Regensburg (Germany). ITP; Kalaydzhyan, T. [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Polikarpov, M.I. [Institute of Theoretical and Experimental Physics, Moscow (Russian Federation)

    2013-02-15

    We study some of the local CP-odd and magnetic properties of the non-Abelian vacuum with use of overlap fermions within the quenched lattice gauge theory. Among these properties are the following: inhomogeneous spatial distribution of the topological charge density (chirality for massless fermions) in SU(2) gluodynamics (for uncooled gauge configurations the chirality is localized on low-dimensional defects with d=2.3, while a sequence of cooling steps gives rise to four-dimensional instantons and hence a four-dimensional structure of the chirality distribution); finite local fluctuations of the chirality growing with the strength of an external magnetic field; magnetization and susceptibility of the QCD vacuum in SU(3) theory; magnetic catalysis of the chiral symmetry breaking, and the electric conductivity of the QCD vacuum in strong magnetic fields.

  9. Quantized gauge field

    International Nuclear Information System (INIS)

    Arodz, H.

    1987-01-01

    The two formulations of quantum theory of the free electromagnetic field are presented. In the Coulomb gauge approach the independent dynamical variables have been identified and then, in order to quantize the theory, it has been sufficient to apply the straightforward canonical quantization. In the Gupta-Bleuler approach the auxilliary theory is first considered. The straightforward canonical quantization of it leads to the quantum theory defined in the space G with indefinite norm. 15 refs. (author)

  10. Velocity-induced heavy quarkonium dissociation using the gauge-gravity correspondence

    Science.gov (United States)

    Patra, Binoy Krishna; Khanchandani, Himanshu; Thakur, Lata

    2015-10-01

    Using the gauge-gravity duality, we have obtained the potential between a heavy quark and an antiquark pair, which is moving perpendicular to the direction of orientation, in a strongly coupled supersymmetric hot plasma. For this purpose we work on a metric in the gravity side, viz. Ouyang-Klebanov-Strassler black hole geometry, of which the dual in the gauge theory side runs with the energy and hence proves to be a better background for thermal QCD. The potential obtained has a confining term both in the vacuum and in a medium, in addition to the Coulomb term alone, usually reported in the literature. As the velocity of the pair is increased, the screening of the potential gets weakened, which may be understood by the decrease of the effective temperature with the increase of the velocity. The crucial observation of our work is that, beyond a critical separation of the heavy quark pair, the potential develops an imaginary part which is nowadays understood to be the main source of dissociation. The imaginary part is found to vanish at small r , thus agreeing with the perturbative result. Finally we have estimated the thermal width for the ground and first excited states and found that nonzero rapidities lead to an increase of thermal width. This implies that the moving quarkonia dissociate more easily than the static ones, which agrees with other calculations. However, the width in our case is larger than other calculations due to the presence of confining terms.

  11. Non-perturbative supersymmetry anomaly in supersymmetric QCD

    International Nuclear Information System (INIS)

    Shamir, Y.

    1991-03-01

    The zero modes of the Dirac operator in an instanton and other topologically non-trivial backgrounds are unstable in a large class of massless or partially massless supersymmetric gauge theories. We show that under a generic perturbation of the scalar fields all zero modes become resonances, and discuss the ensuing breakdown of conventional perturbation theory. As a result, despite of the presence of massless fermions, the field theoretic tunneling amplitude is not suppressed. In massless supersymmetric QCD with N c ≤ N f the effective potential is found to be negative and monotonically increasing in the weak coupling regime for scalar VEVs which lie on the perturbatively flat directions. Consequently, massless supersymmetric QCD with N c ≤ N f exhibits a non-perturbative supersymmetry anomaly and exists in a strongly interacting phase which closely resembles ordinary QCD. The same conclusions apply if small masses are added to the lagrangian and the massless limit is smooth. (author). 21 refs, 5 figs

  12. From notes to chords in QCD

    International Nuclear Information System (INIS)

    Wilczek, F.

    1998-01-01

    After a very brief overview recollecting the 'classic' parts of QCD, that is its application to describe hard processes and static properties of hadrons, I survey recent work - some very recent - on QCD at non-zero temperature and density. At finite temperature and zero density there is a compelling theoretical framework allowing us to predict highly specific, non-trivial dependence of the phase structure on the number of flavors and colors. Several aspects have been rigorously, and successfully, tested against massive numerical realizations of the microscopic theory. The theoretical description of high density is nowhere near as mature, but some intriguing possibilities have been put forward. The color/flavor locked state recently proposed for three flavors has many remarkable features connected to its basic symmetry structure, notably including chiral symmetry re-breaking and the existence (unlike for two flavors) of a gauge invariant order parameter. I survey potential applications to heavy ion collisions, astrophysics, and cosmology. A noteworthy possibility is that stellar explosions are powered by release of QCD latent heat. (orig.)

  13. Electron transport in the presence of a Coulomb field

    International Nuclear Information System (INIS)

    Burgdoerfer, J.; Gibbons, J.

    1990-01-01

    We analyze the modifications of the transport behavior of electrons in dense media due to the presence of a strong Coulomb field generated by an ion moving initially in close phase-space correlation with the electrons. These modifications play a profound role in convoy electron emission in ion-solid collisions. The transport behavior is studied within the framework of a classical phase-space master equation. The nonseparable master equation is solved numerically using test-particle discretization and Monte Carlo sampling. In the limit of vanishing Coulomb forces the master equation becomes separable and can be reduced to standard one-dimensional kinetic equations for free-electron transport that can be solved exactly. The comparison to free-electron transport is used to gauge both the reliability of test-particle discretization and the significance of Coulomb distortion of the distribution functions. Applications to convoy-electron emission are discussed

  14. Study of the structure of the QCD vacuum by means of overlap fermions; Untersuchung der Struktur des QCD-Vakuums mit Hilfe von Overlap-Fermionen

    Energy Technology Data Exchange (ETDEWEB)

    Weinberg, Volker

    2008-12-15

    In this thesis the structure of the QCD vacuum and the nature of the chiral phase transition were studied by means of overlap fermions. The main topic of the theiss lies in the study of the infrared long-range aspects shown by the low-lying eigenmodes of the overlap operator. For the characterization of the structure and dimension of an arbitray density embedded in the four-dimensional space-time diverse analysis tools were developed. These are applied both at low temperature (T=0) in the valence-quark approximation of QCD and in the environment of the high-temperature phase transition of the full QCD for the description of the structure of the modes and the topological density, as well as for the analysis of the local self-duality of the basing gauge fields.

  15. Lattice QCD simulation of meson exchange forces

    International Nuclear Information System (INIS)

    Richards, D.G.; Sinclair, D.K.; Sivers, D.

    1990-01-01

    We present the formalism for investigating the bar Qq bar Qq system in lattice QCD. This system serves as a model for describing exchange forces between heavy, static hadrons. We use this formalism to calculate the exchange potential from gauge configurations which incorporate the effects of dynamical quarks. Our data can be interpreted as giving preliminary results on the range of the nuclear force

  16. An Anderson-like model of the QCD chiral transition

    International Nuclear Information System (INIS)

    Giordano, Matteo; Kovács, Tamás G.; Pittler, Ferenc

    2016-01-01

    We study the problems of chiral symmetry breaking and eigenmode localisation in finite-temperature QCD by looking at the lattice Dirac operator as a random Hamiltonian. We recast the staggered Dirac operator into an unconventional three-dimensional Anderson Hamiltonian (“Dirac-Anderson Hamiltonian”) carrying internal degrees of freedom, with disorder provided by the fluctuations of the gauge links. In this framework, we identify the features relevant to chiral symmetry restoration and localisation of the low-lying Dirac eigenmodes in the ordering of the local Polyakov lines, and in the related correlation between spatial links across time slices, thus tying the two phenomena to the deconfinement transition. We then build a toy model based on QCD and on the Dirac-Anderson approach, replacing the Polyakov lines with spin variables and simplifying the dynamics of the spatial gauge links, but preserving the above-mentioned relevant dynamical features. Our toy model successfully reproduces the main features of the QCD spectrum and of the Dirac eigenmodes concerning chiral symmetry breaking and localisation, both in the ordered (deconfined) and disordered (confined) phases. Moreover, it allows us to study separately the roles played in the two phenomena by the diagonal and the off-diagonal terms of the Dirac-Anderson Hamiltonian. Our results support our expectation that chiral symmetry restoration and localisation of the low modes are closely related, and that both are triggered by the deconfinement transition.

  17. Quenching parameter in a holographic thermal QCD

    Directory of Open Access Journals (Sweden)

    Binoy Krishna Patra

    2017-01-01

    Full Text Available We have calculated the quenching parameter, qˆ in a model-independent way using the gauge–gravity duality. In earlier calculations, the geometry in the gravity side at finite temperature was usually taken as the pure AdS black hole metric for which the dual gauge theory becomes conformally invariant unlike QCD. Therefore we use a metric which incorporates the fundamental quarks by embedding the coincident D7 branes in the Klebanov–Tseytlin background and a finite temperature is switched on by inserting a black hole into the background, known as OKS-BH metric. Further inclusion of an additional UV cap to the metric prepares the dual gauge theory to run similar to thermal QCD. Moreover qˆ is usually defined in the literature from the Glauber model perturbative QCD evaluation of the Wilson loop, which has no reasons to hold if the coupling is large and is thus against the main idea of gauge–gravity duality. Thus we use an appropriate definition of qˆ: qˆL−=1/L2, where L is the separation for which the Wilson loop is equal to some specific value. The above two refinements cause qˆ to vary with the temperature as T4 always and to depend linearly on the light-cone time L− with an additional (1/L− correction term in the short-distance limit whereas in the long-distance limit, qˆ depends only linearly on L− with no correction term. These observations agree with other holographic calculations directly or indirectly.

  18. Phase diagrams of exceptional and supersymmetric lattice gauge theories

    Energy Technology Data Exchange (ETDEWEB)

    Wellegehausen, Bjoern-Hendrik

    2012-07-10

    In this work different strongly-coupled gauge theories with and without fundamental matter have been studied on the lattice with an emphasis on the confinement problem and the QCD phase diagram at nonvanishing net baryon density as well as on possible supersymmetric extensions of the standard model of particle physics. In gauge theories with a non-trivial centre symmetry, as for instance SU(3)-Yang-Mills theory, confinement is intimately related to the centre of the gauge group, and the Polyakov loop serves as an order parameter for confinement. In QCD, this centre symmetry is explicitly broken by quarks in the fundamental representation of the gauge group. But still quarks and gluons are confined in mesons, baryons and glueballs at low temperatures and small densities, suggesting that centre symmetry is not responsible for the phenomenon of confinement. Therefore it is interesting to study pure gauge theories without centre symmetry. In this work this has been done by replacing the gauge group SU(3) of the strong interaction with the exceptional Lie group G{sub 2}, that has a trivial centre. To investigate G{sub 2} gauge theory on the lattice, a new and highly efficient update algorithm has been developed, based on a local HMC algorithm. Employing this algorithm, the proposed and already investigated first order phase transition from a confined to a deconfined phase has been confirmed, showing that indeed a first order phase transition without symmetry breaking or an order parameter is possible. In this context, also the deconfinement phase transition of the exceptional Lie groups F4 and E6 in three spacetime dimensions has been studied. It has been shown that both theories also possess a first order phase transition.

  19. Phase diagrams of exceptional and supersymmetric lattice gauge theories

    International Nuclear Information System (INIS)

    Wellegehausen, Bjoern-Hendrik

    2012-01-01

    In this work different strongly-coupled gauge theories with and without fundamental matter have been studied on the lattice with an emphasis on the confinement problem and the QCD phase diagram at nonvanishing net baryon density as well as on possible supersymmetric extensions of the standard model of particle physics. In gauge theories with a non-trivial centre symmetry, as for instance SU(3)-Yang-Mills theory, confinement is intimately related to the centre of the gauge group, and the Polyakov loop serves as an order parameter for confinement. In QCD, this centre symmetry is explicitly broken by quarks in the fundamental representation of the gauge group. But still quarks and gluons are confined in mesons, baryons and glueballs at low temperatures and small densities, suggesting that centre symmetry is not responsible for the phenomenon of confinement. Therefore it is interesting to study pure gauge theories without centre symmetry. In this work this has been done by replacing the gauge group SU(3) of the strong interaction with the exceptional Lie group G 2 , that has a trivial centre. To investigate G 2 gauge theory on the lattice, a new and highly efficient update algorithm has been developed, based on a local HMC algorithm. Employing this algorithm, the proposed and already investigated first order phase transition from a confined to a deconfined phase has been confirmed, showing that indeed a first order phase transition without symmetry breaking or an order parameter is possible. In this context, also the deconfinement phase transition of the exceptional Lie groups F4 and E6 in three spacetime dimensions has been studied. It has been shown that both theories also possess a first order phase transition.

  20. Cohomological gauge theory, quiver matrix models and Donaldson-Thomas theoryCohomological gauge theory, quiver matrix models and Donaldson-Thomas theory

    NARCIS (Netherlands)

    Cirafici, M.; Sinkovics, A.; Szabo, R.J.

    2009-01-01

    We study the relation between Donaldson–Thomas theory of Calabi–Yau threefolds and a six-dimensional topological Yang–Mills theory. Our main example is the topological U(N) gauge theory on flat space in its Coulomb branch. To evaluate its partition function we use equivariant localization techniques

  1. A lattice QCD calculation of the transverse decay constant of the b1(1235) meson

    International Nuclear Information System (INIS)

    Jansen, K.; McNeile, C.; Michael, C.; Urbach, C.

    2009-10-01

    We review various B meson decays that require knowledge of the transverse decay constant of the b 1 (1235) meson. We report on an exploratory lattice QCD calculation of the transverse decay constant of the b 1 meson. The lattice QCD calculations used unquenched gauge configurations, at two lattice spacings, generated with two flavours of sea quarks. The twisted mass formalism is used. (orig.)

  2. The Pressure in 2, 2+1 and 3 Flavour QCD

    CERN Document Server

    Karsch, Frithjof; Peikert, A

    2000-01-01

    We calculate the pressure in QCD with two and three light quarks on a latticeof size 16^3x4 using tree level improved gauge and fermion actions. We arguethat for temperatures T > 2T_c systematic effects due to the finite latticecut-off and non-vanishing quark masses are below 15 0n this calculation andgive an estimate for the continuum extrapolated pressure in QCD with masslessquarks. We find that the flavour dependence of the pressure is dominated bythat of the Stefan-Boltzmann constant. Furthermore we perform a calculation ofthe pressure using 2 light (m_u,d/T=0.4) and one heavier quark (m_s/T = 1). Inthis case the pressure is reduced relative to that of three flavour QCD. Thiseffect is stronger than expected from the mass dependence of an ideal Fermigas.

  3. Infrared Fixed Point Physics in ${\\rm SO}(N_c)$ and ${\\rm Sp}(N_c)$ Gauge Theories

    DEFF Research Database (Denmark)

    Ryttov, Thomas A.; Shrock, Robert

    2017-01-01

    We study properties of asymptotically free vectorial gauge theories with gauge groups $G={\\rm SO}(N_c)$ and $G={\\rm Sp}(N_c)$ and $N_f$ fermions in a representation $R$ of $G$, at an infrared (IR) zero of the beta function, $\\alpha_{IR}$, in the non-Abelian Coulomb phase. The fundamental, adjoint......_{\\bar\\psi\\psi,IR}$ increases monotonically with decreasing $N_f$ in the non-Abelian Coulomb phase. Using this property, we give a new estimate of the lower end of this phase for some specific realizations of these theories....

  4. Lattice QCD Application Development within the US DOE Exascale Computing Project

    Energy Technology Data Exchange (ETDEWEB)

    Brower, Richard [Boston U.; Christ, Norman [Columbia U.; DeTar, Carleton [Utah U.; Edwards, Robert [Jefferson Lab; Mackenzie, Paul [Fermilab

    2017-10-30

    In October, 2016, the US Department of Energy launched the Exascale Computing Project, which aims to deploy exascale computing resources for science and engineering in the early 2020's. The project brings together application teams, software developers, and hardware vendors in order to realize this goal. Lattice QCD is one of the applications. Members of the US lattice gauge theory community with significant collaborators abroad are developing algorithms and software for exascale lattice QCD calculations. We give a short description of the project, our activities, and our plans.

  5. Lattice QCD Application Development within the US DOE Exascale Computing Project

    Science.gov (United States)

    Brower, Richard; Christ, Norman; DeTar, Carleton; Edwards, Robert; Mackenzie, Paul

    2018-03-01

    In October, 2016, the US Department of Energy launched the Exascale Computing Project, which aims to deploy exascale computing resources for science and engineering in the early 2020's. The project brings together application teams, software developers, and hardware vendors in order to realize this goal. Lattice QCD is one of the applications. Members of the US lattice gauge theory community with significant collaborators abroad are developing algorithms and software for exascale lattice QCD calculations. We give a short description of the project, our activities, and our plans.

  6. Lattice QCD Application Development within the US DOE Exascale Computing Project

    Directory of Open Access Journals (Sweden)

    Brower Richard

    2018-01-01

    Full Text Available In October, 2016, the US Department of Energy launched the Exascale Computing Project, which aims to deploy exascale computing resources for science and engineering in the early 2020’s. The project brings together application teams, software developers, and hardware vendors in order to realize this goal. Lattice QCD is one of the applications. Members of the US lattice gauge theory community with significant collaborators abroad are developing algorithms and software for exascale lattice QCD calculations. We give a short description of the project, our activities, and our plans.

  7. On bound states of photons in noncommutative U(1) gauge theory

    International Nuclear Information System (INIS)

    Fatollahi, A.H.; Jafari, A.

    2006-01-01

    We consider the possibility that photons of noncommutative U(1) gauge theory can make bound states. Using the potential model, developed based on the constituent gluon picture of QCD glue-balls, arguments are presented in favor of the existence of these bound states. The basic ingredient of the potential model is that the self-interacting massless gauge particles may get mass by the inclusion of non-perturbative effects. (orig.)

  8. Chiral symmetry breaking and cooling in lattice QCD

    International Nuclear Information System (INIS)

    Woloshyn, R.M.; Lee, F.X.

    1995-08-01

    Chiral symmetry breaking is calculated as a function of cooling in quenched lattice QCD. A non-zero signal is found for the chiral condensate beyond one hundred cooling steps, suggesting that there is chiral symmetry breaking associated with instantons. Quantitatively, the chiral condensate in cooled gauge field configurations is small compared to the value without cooling. (author) 7 refs., 1 tab., 3 figs

  9. Lattice QCD computations: Recent progress with modern Krylov subspace methods

    Energy Technology Data Exchange (ETDEWEB)

    Frommer, A. [Bergische Universitaet GH Wuppertal (Germany)

    1996-12-31

    Quantum chromodynamics (QCD) is the fundamental theory of the strong interaction of matter. In order to compare the theory with results from experimental physics, the theory has to be reformulated as a discrete problem of lattice gauge theory using stochastic simulations. The computational challenge consists in solving several hundreds of very large linear systems with several right hand sides. A considerable part of the world`s supercomputer time is spent in such QCD calculations. This paper presents results on solving systems for the Wilson fermions. Recent progress is reviewed on algorithms obtained in cooperation with partners from theoretical physics.

  10. Electromagnetic form factors at large momenta from lattice QCD

    International Nuclear Information System (INIS)

    Chambers, Alexander J.; Dragos, J.; Michigan State Univ., East Lansing, MI; Horsley, R.

    2017-01-01

    Accessing hadronic form factors at large momentum transfers has traditionally presented a challenge for lattice QCD simulations. Here we demonstrate how a novel implementation of the Feynman-Hellmann method can be employed to calculate hadronic form factors in lattice QCD at momenta much higher than previously accessible. Our simulations are performed on a single set of gauge configurations with three flavours of degenerate mass quarks corresponding to m_π∼470 MeV. We are able to determine the electromagnetic form factors of the pion and nucleon up to approximately 6 GeV"2, with results for G_E/G_M in the proton agreeing well with experimental results.

  11. Running coupling from gluon and ghost propagators in the Landau gauge: Yang-Mills theories with adjoint fermions

    Science.gov (United States)

    Bergner, Georg; Piemonte, Stefano

    2018-04-01

    Non-Abelian gauge theories with fermions transforming in the adjoint representation of the gauge group (AdjQCD) are a fundamental ingredient of many models that describe the physics beyond the Standard Model. Two relevant examples are N =1 supersymmetric Yang-Mills (SYM) theory and minimal walking technicolor, which are gauge theories coupled to one adjoint Majorana and two adjoint Dirac fermions, respectively. While confinement is a property of N =1 SYM, minimal walking technicolor is expected to be infrared conformal. We study the propagators of ghost and gluon fields in the Landau gauge to compute the running coupling in the MiniMom scheme. We analyze several different ensembles of lattice Monte Carlo simulations for the SU(2) adjoint QCD with Nf=1 /2 ,1 ,3 /2 , and 2 Dirac fermions. We show how the running of the coupling changes as the number of interacting fermions is increased towards the conformal window.

  12. Five-dimensional gauge theory and compactification on a torus

    NARCIS (Netherlands)

    Haghighat, B.; Vandoren, S.J.G.

    2011-01-01

    We study five-dimensional minimally supersymmetric gauge theory compactified on a torus down to three dimensions, and its embedding into string/M-theory using geometric engineering. The moduli space on the Coulomb branch is hyperkaehler equipped with a metric with modular transformation properties.

  13. Quantum electrodynamics in the light-front Weyl gauge

    International Nuclear Information System (INIS)

    Przeszowski, J.; Naus, H.W.; Kalloniatis, A.C.

    1996-01-01

    We examine (3+1)-dimensional QED quantized in the open-quote open-quote front form close-quote close-quote with finite open-quote open-quote volume close-quote close-quote regularization, namely, in discretized light-cone quantization. Instead of the light-cone or Coulomb gauges, we impose the light-front Weyl gauge A - =0. The Dirac method is used to arrive at the quantum commutation relations for the independent variables. We apply open-quote open-quote quantum-mechanical gauge fixing close-quote close-quote to implement Gauss close-quote law, and derive the physical Hamiltonian in terms of unconstrained variables. As in the instant form, this Hamiltonian is invariant under global residual gauge transformations, namely, displacements. On the light cone the symmetry manifests itself quite differently. copyright 1996 The American Physical Society

  14. A lattice QCD calculation of the transverse decay constant of the b{sub 1}(1235) meson

    Energy Technology Data Exchange (ETDEWEB)

    Jansen, K. [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC; McNeile, C. [Wuppertal Univ. (Germany). Theoretische Teilchenphysik; Michael, C. [Liverpool Univ. (United Kingdom). Theoretical Physics Division, Dept. of Mathematical Sciences; Urbach, C. [Humboldt-Univ., Berlin (Germany). Theorie der Elementarteilchen

    2009-10-15

    We review various B meson decays that require knowledge of the transverse decay constant of the b{sub 1}(1235) meson. We report on an exploratory lattice QCD calculation of the transverse decay constant of the b{sub 1} meson. The lattice QCD calculations used unquenched gauge configurations, at two lattice spacings, generated with two flavours of sea quarks. The twisted mass formalism is used. (orig.)

  15. QCD and electroweak interference in Higgs production by gauge boson fusion

    International Nuclear Information System (INIS)

    Andersen, Jeppe R.; Smillie, Jennifer M.

    2007-01-01

    We explicitly calculate the contribution to Higgs production at the LHC from the interference between gluon fusion and weak vector boson fusion, and compare it to the pure QCD and pure electroweak result. While the effect is small at tree level, we speculate it will be significantly enhanced by loop effects

  16. New insights into properties of large-N holographic thermal QCD at finite gauge coupling at (the non-conformal/next-to) leading order in N

    International Nuclear Information System (INIS)

    Sil, Karunava; Misra, Aalok

    2016-01-01

    It is believed that large-N thermal QCD laboratories like strongly coupled QGP (sQGP) require not only a large 't Hooft coupling but also a finite gauge coupling (Natsuume, String theory and quark-gluon plasma. arXiv:hep-ph/0701201, 2007). Unlike almost all top-down holographic models in the literature, holographic large-N thermal QCD models, based on this assumption, therefore necessarily require addressing this limit from M-theory. This was initiated in Dhuria and Misra (JHEP 1311:001, 2013) which presented a local M-theory uplift of the string theoretic dual of large-N thermal QCD-like theories at finite gauge/string coupling of Mia et al. (Nucl. Phys. B 839:187, arXiv:0902.1540 [hep-th], 2010) (g s gauge coupling, have been entirely missing in the literature. In this paper we largely address the following two non-trivial issues pertaining to the same. First, up to LO in N (the number of D3-branes), by calculating the temperature dependence of the thermal (and electrical) conductivity and the consequent deviation from the Wiedemann-Franz law, upon comparison with Garg et al. (Phys. Rev. Lett. 103:096402, 2009), we show that, remarkably, the results qualitatively mimic a 1+1-dimensional Luttinger liquid with impurities. Second, by looking at, respectively, the scalar, vector, and tensor modes of metric perturbations and using the prescription of Kovtun and Starinets (Phys. Rev. D 72:086009, arXiv:hep-th/0506184, 2005) for constructing appropriate gauge-invariant perturbations, we obtain the non-conformal corrections to the conformal results (but at finite g s ), respectively, for the speed of sound, the shear mode diffusion constant, and the shear viscosity η (and (η)/(s)). The new insight gained is that it turns out

  17. New insights into properties of large-N holographic thermal QCD at finite gauge coupling at (the non-conformal/next-to) leading order in N

    Energy Technology Data Exchange (ETDEWEB)

    Sil, Karunava; Misra, Aalok [Indian Institute of Technology, Department of Physics, Roorkee, Uttarakhand (India)

    2016-11-15

    It is believed that large-N thermal QCD laboratories like strongly coupled QGP (sQGP) require not only a large 't Hooft coupling but also a finite gauge coupling (Natsuume, String theory and quark-gluon plasma. arXiv:hep-ph/0701201, 2007). Unlike almost all top-down holographic models in the literature, holographic large-N thermal QCD models, based on this assumption, therefore necessarily require addressing this limit from M-theory. This was initiated in Dhuria and Misra (JHEP 1311:001, 2013) which presented a local M-theory uplift of the string theoretic dual of large-N thermal QCD-like theories at finite gauge/string coupling of Mia et al. (Nucl. Phys. B 839:187, arXiv:0902.1540 [hep-th], 2010) (g{sub s} gauge coupling, have been entirely missing in the literature. In this paper we largely address the following two non-trivial issues pertaining to the same. First, up to LO in N (the number of D3-branes), by calculating the temperature dependence of the thermal (and electrical) conductivity and the consequent deviation from the Wiedemann-Franz law, upon comparison with Garg et al. (Phys. Rev. Lett. 103:096402, 2009), we show that, remarkably, the results qualitatively mimic a 1+1-dimensional Luttinger liquid with impurities. Second, by looking at, respectively, the scalar, vector, and tensor modes of metric perturbations and using the prescription of Kovtun and Starinets (Phys. Rev. D 72:086009, arXiv:hep-th/0506184, 2005) for constructing appropriate gauge-invariant perturbations, we obtain the non-conformal corrections to the conformal results (but at finite g{sub s}), respectively, for the speed of sound, the shear mode diffusion constant, and the shear viscosity η (and (η)/(s)). The new insight gained is that it

  18. Full CKM matrix with lattice QCD

    Energy Technology Data Exchange (ETDEWEB)

    Okamoto, Masataka; /Fermilab

    2004-12-01

    The authors show that it is now possible to fully determine the CKM matrix, for the first time, using lattice QCD. |V{sub cd}|, |V{sub cs}|, |V{sub ub}|, |V{sub cb}| and |V{sub us}| are, respectively, directly determined with the lattice results for form factors of semileptonic D {yields} {pi}lv, D {yields} Klv, B {yields} {pi}lv, B {yields} Dlv and K {yields} {pi}lv decays. The error from the quenched approximation is removed by using the MILC unquenced lattice gauge configurations, where the effect of u, d and s quarks is included. The error from the ''chiral'' extrapolation (m{sub l} {yields} m{sub ud}) is greatly reduced by using improved staggered quarks. The accuracy is comparable to that of the Particle Data Group averages. In addition, |V{sub ud}|, |V{sub ts}|, |V{sub ts}| and |V{sub td}| are determined by using unitarity of the CKM matrix and the experimental result for sin (2{beta}). In this way, they obtain all 9 CKM matrix elements, where the only theoretical input is lattice QCD. They also obtain all the Wolfenstein parameters, for the first time, using lattice QCD.

  19. Massively Parallel QCD

    International Nuclear Information System (INIS)

    Soltz, R; Vranas, P; Blumrich, M; Chen, D; Gara, A; Giampap, M; Heidelberger, P; Salapura, V; Sexton, J; Bhanot, G

    2007-01-01

    The theory of the strong nuclear force, Quantum Chromodynamics (QCD), can be numerically simulated from first principles on massively-parallel supercomputers using the method of Lattice Gauge Theory. We describe the special programming requirements of lattice QCD (LQCD) as well as the optimal supercomputer hardware architectures that it suggests. We demonstrate these methods on the BlueGene massively-parallel supercomputer and argue that LQCD and the BlueGene architecture are a natural match. This can be traced to the simple fact that LQCD is a regular lattice discretization of space into lattice sites while the BlueGene supercomputer is a discretization of space into compute nodes, and that both are constrained by requirements of locality. This simple relation is both technologically important and theoretically intriguing. The main result of this paper is the speedup of LQCD using up to 131,072 CPUs on the largest BlueGene/L supercomputer. The speedup is perfect with sustained performance of about 20% of peak. This corresponds to a maximum of 70.5 sustained TFlop/s. At these speeds LQCD and BlueGene are poised to produce the next generation of strong interaction physics theoretical results

  20. Lattice-QCD based Schwinger-Dyson approach for Chiral phase transition

    International Nuclear Information System (INIS)

    Iida, Hideaki; Oka, Makoto; Suganuma, Hideo

    2005-01-01

    Dynamical chiral-symmetry breaking in QCD is studied with the Schwinger-Dyson (SD) formalism based on lattice QCD data, i.e., LQCD-based SD formalism. We extract the SD kernel function K(p 2 ) in an Ansatzindependent manner from the lattice data of the quark propagator in the Landau gauge. As remarkable features, we find infrared vanishing and intermediate enhancement of the SD kernel function K(p 2 ). We apply the LQCD-based SD equation to thermal QCD with the quark chemical potential μ q . We find chiral symmetry restoration at T c ∼100MeV for μ q =0. The real part of the quark mass function decreases as T and μ q . At finite density, there appears the imaginary part of the quark mass function, which would lead to the width broadening of hadrons

  1. National Computational Infrastructure for Lattice Gauge Theory: Final Report

    International Nuclear Information System (INIS)

    Richard Brower; Norman Christ; Michael Creutz; Paul Mackenzie; John Negele; Claudio Rebbi; David Richards; Stephen Sharpe; Robert Sugar

    2006-01-01

    This is the final report of Department of Energy SciDAC Grant ''National Computational Infrastructure for Lattice Gauge Theory''. It describes the software developed under this grant, which enables the effective use of a wide variety of supercomputers for the study of lattice quantum chromodynamics (lattice QCD). It also describes the research on and development of commodity clusters optimized for the study of QCD. Finally, it provides some high lights of research enabled by the infrastructure created under this grant, as well as a full list of the papers resulting from research that made use of this infrastructure

  2. Soft thermal contributions to 3-loop gauge coupling

    Science.gov (United States)

    Laine, M.; Schicho, P.; Schröder, Y.

    2018-05-01

    We analyze 3-loop contributions to the gauge coupling felt by ultrasoft ("magnetostatic") modes in hot Yang-Mills theory. So-called soft/hard terms, originating from dimension-six operators within the soft effective theory, are shown to cancel 1097/1098 of the IR divergence found in a recent determination of the hard 3-loop contribution to the soft gauge coupling. The remaining 1/1098 originates from ultrasoft/hard contributions, induced by dimension-six operators in the ultrasoft effective theory. Soft 3-loop contributions are likewise computed, and are found to be IR divergent, rendering the ultrasoft gauge coupling non-perturbative at relative order O({α}s^{3/2}) . We elaborate on the implications of these findings for effective theory studies of physical observables in thermal QCD.

  3. The electromagnetic potentials without the gauge transformations

    Energy Technology Data Exchange (ETDEWEB)

    Espinoza, Augusto; Chubykalo, Andrey; Rodriguez, Alejandro Gutierrez; Hernandez, Maria de los Angeles [Universidad Autonoma de Zacatecas (Mexico). Unidad Academica de Fisica

    2011-07-01

    In this note we show that the use of the Helmholtz theorem lead to derivation of uniquely determined electromagnetic potentials without making use of the gauge transformation. These potentials correspond to the potentials obtained by imposing so-called Coulomb condition (gauge) in the traditional approach. We show that the electromagnetic field comprises two components, one of which is characterized by its instantaneous action at a distance, whereas another one propagates in the retarded form with the velocity of light. One of the theoretical consequences of this new definition is that the electromagnetic potentials are real physical quantities as well as the electric and magnetic fields. We show that the reality of the electromagnetic potentials in quantum-mechanics is also a property of these potentials in the classical electrodynamics. Equations for potentials obtained in our approach are already separated with respect to vector and scalar potentials, so there is no necessity in using the gauge transformations and, accordingly, in making use of either Lorentz or Coulomb condition. The vector potential and scalar potential introduced thus are uniquely defined. The scalar potential is a generator of the so called instantaneous action at a distance, whereas the solenoidal vector potential can propagate with the velocity of light and it is responsible for the retarded action of the electromagnetic field. (author)

  4. Virtual Compton Scattering off a Spinless Target in the AdS/QCD correspondence

    CERN Document Server

    Marquet, C.; Wallon, S.

    2010-01-01

    We perform a study of the doubly virtual Compton scattering off a spinless target gamma* P -> gamma* P' within the Anti-de Sitter(AdS)/QCD formalism. We find that the general structure allowed by the Lorentz invariance and gauge invariance of the Compton amplitude is not easily reproduced with the standard recipes of the AdS/QCD correspondence. In the soft-photon regime, where the semi-classical approximation is supposed to apply best, we show that the measurements of the electric and magnetic polarizabilities of a target like the charged pion in real Compton scattering, can already serve as stringent tests, and presumably exclude results based on the AdS/QCD correspondence in its minimal version.

  5. Phenomenology of strongly coupled chiral gauge theories

    International Nuclear Information System (INIS)

    Bai, Yang; Berger, Joshua; Osborne, James; Stefanek, Ben A.

    2016-01-01

    A sector with QCD-like strong dynamics is common in models of non-standard physics. Such a model could be accessible in LHC searches if both confinement and big-quarks charged under the confining group are at the TeV scale. Big-quark masses at this scale can be explained if the new fermions are chiral under a new U(1) ′ gauge symmetry such that their bare masses are related to the U(1) ′ -breaking and new confinement scales. Here we present a study of a minimal GUT-motivated and gauge anomaly-free model with implications for the LHC Run 2 searches. We find that the first signatures of such models could appear as two gauge boson resonances. The chiral nature of the model could be confirmed by observation of a Z ′ γ resonance, where the Z ′ naturally has a large leptonic branching ratio because of its kinetic mixing with the hypercharge gauge boson.

  6. A map between corner and link operators in lattice gauge theories

    International Nuclear Information System (INIS)

    Bars, I.

    1979-01-01

    A completely local gauge-invariant lattice gauge theory is formulated in terms of a new set of variables introduced earlier in the continuum. This theory uses local 'corner' variables defined on lattice sites only, as opposed to the conventional 'link' variables. It is shown via a map that the formulation gives identical results to the usual lattice gauge theory. The properties of the quantum commutators in the continuum limit is also discussed and contrasted for the two lattice approaches. In terms of the corner operators the quantized lattice theory is seen to be closely related to continuum QCD. (Auth.)

  7. Phase transitions and flux distributions of SU(2) lattice gauge theory

    International Nuclear Information System (INIS)

    Peng, Yingcai.

    1993-01-01

    The strong interactions between quarks are believed to be described by Quantum Chromodynamics (QCD), which is a non-abelian SU(3) gauge theory. It is known that QCD undergoes a deconfining phase transition at very high temperatures, that is, at low temperatures QCD is in confined phase, at sufficient high temperatures it is in an unconfined phase. Also, quark confinement is believed to be due to string formation. In this dissertation the authors studied SU(2) gauge theory using numerical methods of LGT, which will provide some insights about the properties of QCD because SU(2) is similar to SU(3). They measured the flux distributions of a q bar q pair at various temperatures in different volumes. They find that in the limit of infinite volumes the flux distribution is different in the two phases. In the confined phase strong evidence is found for the string formation, however, in the unconfined phase there is no string formation. On the other hand, in the limit of zero temperature and finite volumes they find a clear signal for string formation in the large volume region, however, the string tension measured in intermediate volumes is due to finite volume effects, there is no intrinsic string formation. The color flux energies (action) of the q bar q pair are described by Michael sum rules. The original Michael sum rules deal with a static q bar q pair at zero temperature in infinite volumes. To check these sum rules with flux data at finite temperatures, they present a complete derivation for the sum rules, thus generalizing them to account for finite temperature effects. They find that the flux data are consistent with the prediction of generalized sum rules. The study elucidates the rich structures of QCD, and provides evidence for quark confinement and string formation. This supports the belief that QCD is a correct theory for strong interactions, and quark confinement can be explained by QCD

  8. Fermion frontiers in vector lattice gauge theories: Proceedings. Volume 8

    International Nuclear Information System (INIS)

    1998-01-01

    The inclusion of fermions into simulations of lattice gauge theories is very difficult both theoretically and numerically. With the presence of Teraflops-scale computers for lattice gauge theory, the authors wanted a forum to discuss new approaches to lattice fermions. The workshop concentrated on approaches which are ripe for study on such large machines. Although lattice chiral fermions are vitally important to understand, there is not technique at hand which is viable on these Teraflops-scale machines for real-world problems. The discussion was therefore focused on recent developments and future prospects for QCD-like theories. For the well-known fermion formulations, the Aoki phase in Wilson fermions, novelties of U A (1) symmetry and the η' for staggered fermions and new approaches for simulating the determinant for Wilson fermions were discussed. The newer domain-wall fermion formulation was reviewed, with numerical results given by many speakers. The fermion proposal of Friedberg, Lee and Pang was introduced. They also were able to compare and contrast the dependence of QCD and QCD-like SUSY theories on the number of quark flavors. These proceedings consist of several transparencies and a summary page from each speaker. This should serve to outline the major points made in each talk

  9. Hard-Thermal-Loop QCD thermodynamics and quark number susceptibility

    Directory of Open Access Journals (Sweden)

    Mogliacci Sylvain

    2014-04-01

    Full Text Available The weak-coupling expansion of the QCD pressure is known up to the order g6 log g. However, at experimentally relevant temperatures, the corresponding series is poorly convergent. In this proceedings, we discuss at which extent the gauge-invariant resummation scheme, Hard-Thermal-Loop perturbation theory (HTLpt, improves the apparent convergence. We first present HTLpt results for QCD thermodynamic functions up to three-loop order at vanishing chemical potential. Then, we report a preliminary HTLpt result of one-loop quark number susceptibility, probing the finite density equation of state. Our results are consistent with lattice data down to 2 − 3Tc, reinforcing the weakly-coupled quasiparticle picture in the intermediate coupling regime.

  10. Exploring the nucleon structure from first principles of QCD

    Energy Technology Data Exchange (ETDEWEB)

    Bietenholz, W. [Universidad Nacional Autonoma de Mexico (Mexico). Inst. de Ciencias Nucleares; Cundy, N.; Goeckeler, M. [Regensburg Univ. (DE). Inst. fuer Theoretische Physik] (and others)

    2010-04-15

    Quantum Chromodynamics (QCD) is generally assumed to be the fundamental theory underlying nuclear physics. In recent years there is progress towards investigating the nucleon structure from first principles of QCD. Although this structure is best revealed in Deep Inelastic Scattering, a consistent analysis has to be performed in a fully non-perturbative scheme. The only known method for this purpose are lattice simulations. We first sketch the ideas of Monte Carlo simulations in lattice gauge theory. Then we comment in particular on the issues of chiral symmetry and operator mixing. Finally we present our results for the Bjorken variable of a single quark, and for the second Nachtmann moment of the nucleon structure functions. (orig.)

  11. Exploring the nucleon structure from first principles of QCD

    International Nuclear Information System (INIS)

    Bietenholz, W.; Cundy, N.; Goeckeler, M.

    2010-04-01

    Quantum Chromodynamics (QCD) is generally assumed to be the fundamental theory underlying nuclear physics. In recent years there is progress towards investigating the nucleon structure from first principles of QCD. Although this structure is best revealed in Deep Inelastic Scattering, a consistent analysis has to be performed in a fully non-perturbative scheme. The only known method for this purpose are lattice simulations. We first sketch the ideas of Monte Carlo simulations in lattice gauge theory. Then we comment in particular on the issues of chiral symmetry and operator mixing. Finally we present our results for the Bjorken variable of a single quark, and for the second Nachtmann moment of the nucleon structure functions. (orig.)

  12. Electromagnetic form factors at large momenta from lattice QCD

    Science.gov (United States)

    Chambers, A. J.; Dragos, J.; Horsley, R.; Nakamura, Y.; Perlt, H.; Pleiter, D.; Rakow, P. E. L.; Schierholz, G.; Schiller, A.; Somfleth, K.; Stüben, H.; Young, R. D.; Zanotti, J. M.; Qcdsf/Ukqcd/Cssm Collaborations

    2017-12-01

    Accessing hadronic form factors at large momentum transfers has traditionally presented a challenge for lattice QCD simulations. Here, we demonstrate how a novel implementation of the Feynman-Hellmann method can be employed to calculate hadronic form factors in lattice QCD at momenta much higher than previously accessible. Our simulations are performed on a single set of gauge configurations with three flavors of degenerate mass quarks corresponding to mπ≈470 MeV . We are able to determine the electromagnetic form factors of the pion and nucleon up to approximately 6 GeV2 , with results for the ratio of the electric and magnetic form factors of the proton at our simulated quark mass agreeing well with experimental results.

  13. The coherent state variational algorithm and the QCD deconfinement phase transition

    International Nuclear Information System (INIS)

    Somsky, W.R.

    1989-01-01

    This thesis describes the coherent state variational algorithm, its implementation in a recently completed set of computer programs, and its application to the study of the QCD deconfinement phase transition. The coherent state variational algorithm is a computational method for studying the large-N limit of non-abelian gauge theories by direct exploitation of the classical nature of this limit. Unlike Monte Carlo methods, this technique is applicable to both euclidean and hamiltonian formulations of lattice gauge theories and is deterministic, rather than statistical, in nature. The first part of this thesis presents the theoretical basis of the coherent state algorithm and describes the application of the algorithm, to non-abelian lattice gauge theories. The second part describes the symbolic methods involved in the computer implementation of the coherent state algorithm and gives an overview of the programs which form the full coherent state implementation. The final part of this thesis discusses the application of the coherent state algorithm to the study of the QCD deconfinement phase transition at large N. The results obtained are indicative of a second-order transition for lattices of temporal extent N ν = 1 and N τ = 2 in both three and four space-time dimensions

  14. Applications of Jarzynski's relation in lattice gauge theories

    DEFF Research Database (Denmark)

    Nada, Alessandro; Caselle, Michele; Costagliola, Gianluca

    2016-01-01

    Jarzynski's equality is a well-known result in statistical mechanics, relating free-energy differences between equilibrium ensembles with fluctuations in the work performed during non-equilibrium transformations from one ensemble to the other. In this work, an extension of this relation to lattice...... gauge theory will be presented, along with numerical results for the ℤ2 gauge model in three dimensions and for the equation of state in SU(2) Yang-Mills theory in four dimensions. Then, further applications will be discussed, in particular for the Schrödinger functional and for the study of QCD...

  15. On the topological vacuum degeneracy in gauge theories

    International Nuclear Information System (INIS)

    Pervushin, V.N.

    1982-01-01

    It is shown that the nontrivial topology of gauge fields leads to the Josephson effect in the field space, i. e., to nonvanishing vacuum fields. The same definition is proposed for the physical (infrared) vacuum for Abelian (QED) and nonAbelian (QCD) theories. The equations and the topological Josephson effect for the gluon vacuum are discussed

  16. Decay constants in soft wall AdS/QCD revisited

    Directory of Open Access Journals (Sweden)

    Nelson R.F. Braga

    2016-12-01

    We show here that a modified framework of soft wall AdS/QCD involving an additional dimensionfull parameter, associated with an ultraviolet energy scale, provides decay constants decreasing with radial excitation level. In this version of the soft wall model the two point function of gauge theory operators is calculated at a finite position of the anti-de Sitter space radial coordinate.

  17. Anomaly matching conditions and the moduli space of supersymmetric gauge theories

    International Nuclear Information System (INIS)

    Dotti, G.; Manohar, A.V.

    1998-01-01

    The structure of the moduli space of N=1 supersymmetric gauge theories is analyzed from an algebraic geometric viewpoint. The connection between the fundamental fields of the ultraviolet theory, and the gauge-invariant composite fields of the infrared theory is explained in detail. The results are then used to prove an anomaly matching theorem. The theorem is used to study anomaly matching for supersymmetric QCD, and can explain all the known anomaly matching results for this case. (orig.)

  18. Vacuum structure and QCD sum rules

    International Nuclear Information System (INIS)

    Shifman, M.A.

    1992-01-01

    The method of the QCD sum rules was and still is one of the most productive tools in a wide range of problems associated with the hadronic phenomenology. Many heuristic ideas, computational devices, specific formulae which are useful to theorists working not only in hadronic physics, have been accumulated in this method. Some of the results and approaches which have originally been developed in connection with the QCD sum rules can be and are successfully applied in related fields, as supersymmetric gauge theories, nontraditional schemes of quarks and leptons, etc. The amount of literature on these and other more basic problems in hadronic physics has grown enormously in recent years. This volume presents a collection of papers which provide an overview of all basic elements of the sum rule approach and priority has been given to the works which seemed most useful from a pedagogical point of view

  19. Vacuum structure and QCD sum rules

    International Nuclear Information System (INIS)

    Shifman, M.A.

    1992-01-01

    The method of the QCD sum rules was and still is one of the most productive tools in a wide range of problems associated with the hadronic phenomenology. Many heuristic ideas, computational devices, specific formulae which are useful to theorists working not only in hadronic physics, have been accumulated in this method. Some of the results and approaches which have been originally developed in connection with the QCD sum rules can be and are successfully applied in related fields, such as supersymmetric gauge theories, nontraditional schemes of quarks and leptons, etc. The amount of literature on these and other more basic problems in hadronic physics has grown enormously in recent years. This collection of papers provides an overview of all basic elements of the sum rule approach. Priority has been given to those works which seemed most useful from a pedagogical point of view

  20. Two-loop master integrals for the leading QCD corrections to the Higgs coupling to a W pair and to the triple gauge couplings ZWW and γ{sup *}WW

    Energy Technology Data Exchange (ETDEWEB)

    Di Vita, Stefano [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Mastrolia, Pierpaolo; Primo, Amedeo [Padova Univ. (Italy). Dipt. di Fisica ed Astronomia; INFN, Padova (Italy); Schubert, Ulrich [Argonne National Laboratory, Argonne, IL (United States). High Energy Physics Div.

    2017-02-15

    We compute the two-loop master integrals required for the leading QCD corrections to the interaction vertex of a massive neutral boson X{sup 0}, e.g. H,Z or γ*, with a pair of W bosons, mediated by a SU(2){sub L} quark doublet composed of one massive and one massless flavor. All the external legs are allowed to have arbitrary invariant masses. The Magnus exponential is employed to identify a set of master integrals that, around d=4 space-time dimensions, obey a canonical system of differential equations. The canonical master integrals are given as a Taylor series in ε=(4-d)/2, up to order four, with coeffcients written as combination of Goncharov polylogarithms, respectively up to weight four. In the context of the Standard Model, our results are relevant for the mixed EW-QCD corrections to the Higgs decay to a W pair, as well as to the production channels obtained by crossing, and to the triple gauge boson vertices ZWW and γ{sup *}WW.

  1. The infrared behaviour of the running coupling in Landau gauge QCD

    International Nuclear Information System (INIS)

    Alkofer, R.; Fischer, C.S.; Smekal, L. von.

    2002-01-01

    Approximate solutions for the gluon and ghost propagators as well as the running coupling in Landau gauge Yang-Mills theories are presented. These propagators obtained from the corresponding Dyson-Schwinger equations are in remarkable agreement with those of recent lattice calculations. The resulting running coupling possesses an infrared fixed point, α s (0) = 8.92/N for all gauge SU(N). Above one GeV the running coupling rapidly approaches its perturbative form (Authors)

  2. Conformal Symmetry as a Template for QCD

    Energy Technology Data Exchange (ETDEWEB)

    Brodsky, S

    2004-08-04

    Conformal symmetry is broken in physical QCD; nevertheless, one can use conformal symmetry as a template, systematically correcting for its nonzero {beta} function as well as higher-twist effects. For example, commensurate scale relations which relate QCD observables to each other, such as the generalized Crewther relation, have no renormalization scale or scheme ambiguity and retain a convergent perturbative structure which reflects the underlying conformal symmetry of the classical theory. The ''conformal correspondence principle'' also dictates the form of the expansion basis for hadronic distribution amplitudes. The AdS/CFT correspondence connecting superstring theory to superconformal gauge theory has important implications for hadron phenomenology in the conformal limit, including an all-orders demonstration of counting rules for hard exclusive processes as well as determining essential aspects of hadronic light-front wavefunctions. Theoretical and phenomenological evidence is now accumulating that QCD couplings based on physical observables such as {tau} decay become constant at small virtuality; i.e., effective charges develop an infrared fixed point in contradiction to the usual assumption of singular growth in the infrared. The near-constant behavior of effective couplings also suggests that QCD can be approximated as a conformal theory even at relatively small momentum transfer. The importance of using an analytic effective charge such as the pinch scheme for unifying the electroweak and strong couplings and forces is also emphasized.

  3. Conformal Symmetry as a Template for QCD

    International Nuclear Information System (INIS)

    Brodsky, S

    2004-01-01

    Conformal symmetry is broken in physical QCD; nevertheless, one can use conformal symmetry as a template, systematically correcting for its nonzero β function as well as higher-twist effects. For example, commensurate scale relations which relate QCD observables to each other, such as the generalized Crewther relation, have no renormalization scale or scheme ambiguity and retain a convergent perturbative structure which reflects the underlying conformal symmetry of the classical theory. The ''conformal correspondence principle'' also dictates the form of the expansion basis for hadronic distribution amplitudes. The AdS/CFT correspondence connecting superstring theory to superconformal gauge theory has important implications for hadron phenomenology in the conformal limit, including an all-orders demonstration of counting rules for hard exclusive processes as well as determining essential aspects of hadronic light-front wavefunctions. Theoretical and phenomenological evidence is now accumulating that QCD couplings based on physical observables such as τ decay become constant at small virtuality; i.e., effective charges develop an infrared fixed point in contradiction to the usual assumption of singular growth in the infrared. The near-constant behavior of effective couplings also suggests that QCD can be approximated as a conformal theory even at relatively small momentum transfer. The importance of using an analytic effective charge such as the pinch scheme for unifying the electroweak and strong couplings and forces is also emphasized

  4. Gauge invariance and the quark-antiquark static potential

    International Nuclear Information System (INIS)

    Cahill, K.; Stump, D.R.

    1979-01-01

    We calculate the quark-antiquark static potential to order g 4 in temporal-gauge quantum chromodynamics by constructing a suitably general family of gauge-invariant qq-bar states and then selecting the one whose energy is minimal for a given qq-bar separation r. Our results agree with those of conventional perturbation theory. We study various ways in which quark confinement might arise from nonperturbative effects related to the Gribov ambiguity. We find that the presence of long-range gauge fields can change the asymptotic behavior of the Coulomb Green's function from r -1 to r/sup -1/2/. We illustrate this possibility by a simple example. After making some simplifying assumptions, we obtain a minimally confining potential V (r) that rises logarithmically for large r

  5. Dissociation of 1P states in hot QCD Medium Using Quasi-Particle Model

    Science.gov (United States)

    Nilima, Indrani; Agotiya, Vineet Kumar

    2018-03-01

    We extend the analysis of a very recent work [1] to study the dissociation phenomenon of 1P states of the charmonium and bottomonium spectra (χc and χb) in a hot QCD medium using Quasi-Particle Model. This study employed a medium modified heavy quark potential which has quite different form in the sense that it has a lomg range Coulombic tail in addition to the Yukawa term even above the deconfinement temperature. Then we study the flavor dependence of their binding energies and explore the nature of dissociation temperatures by employing the Quasi-Particle debye mass for pure gluonic and full QCD case. Interestingly, the dissociation temperatures obtained by employing EoS1 and EoS2 with the Γ criterion, is closer to the upper bound of the dissociation temperatures which are obtained by the dissolution of a given quarkonia state by the mean thermal energy of the quasi-partons in the hot QCD/QGP medium.

  6. New relations for gauge-theory amplitudes

    International Nuclear Information System (INIS)

    Bern, Z.; Carrasco, J. J. M.; Johansson, H.

    2008-01-01

    We present an identity satisfied by the kinematic factors of diagrams describing the tree amplitudes of massless gauge theories. This identity is a kinematic analog of the Jacobi identity for color factors. Using this we find new relations between color-ordered partial amplitudes. We discuss applications to multiloop calculations via the unitarity method. In particular, we illustrate the relations between different contributions to a two-loop four-point QCD amplitude. We also use this identity to reorganize gravity tree amplitudes diagram by diagram, offering new insight into the structure of the Kawai-Lewellen-Tye (KLT) relations between gauge and gravity tree amplitudes. This insight leads to similar but novel relations. We expect this to be helpful in higher-loop studies of the ultraviolet properties of gravity theories.

  7. Fundamental problems of gauge field theory

    International Nuclear Information System (INIS)

    Velo, G.; Wightman, A.S.

    1986-01-01

    As a result of the experimental and theoretical developments of the last two decades, gauge field theory, in one form or another, now provides the standard language for the description of Nature; QCD and the standard model of the electroweak interactions illustrate this point. It is a basic task of mathematical physics to provide a solid foundation for these developments by putting the theory in a physically transparent and mathematically rigorous form. The lecture notes collected in this volume concentrate on the many unsolved problems which arise here, and on the general ideas and methods which have been proposed for their solution. In particular, the use of rigorous renormalization group methods to obtain control over the continuum limit of lattice gauge field theories, the exploration of the extraordinary enigmatic connections between Kac-Moody-Virasoro algebras and string theory, and the systematic use of the theory of local algebras and indefinite metric spaces to classify the charged C* states in gauge field theories are mentioned

  8. Evidence for the existence of Gribov copies in Landau gauge lattice QCD

    Energy Technology Data Exchange (ETDEWEB)

    Marinari, E.; Ricci, R. (Rome-2 Univ. (Italy). Dipt. di Fisica INFN, Rome (Italy)); Parrinello, C. (New York Univ., NY (USA). Physics Dept.)

    1991-09-16

    We unambiguously show the existence of Gribov copies in a pure SU(3) gauge lattice model, with Wilson action. We show that the usual steepest-descent algorithms used for implementing the lattice Landau gauge lead to ambiguities, which are related to the existence of Gribov copies in the model. (orig.).

  9. QCD in heavy quark production and decay

    Energy Technology Data Exchange (ETDEWEB)

    Wiss, J. [Univ. of Illinois, Urbana, IL (United States)

    1997-06-01

    The author discusses how QCD is used to understand the physics of heavy quark production and decay dynamics. His discussion of production dynamics primarily concentrates on charm photoproduction data which are compared to perturbative QCD calculations which incorporate fragmentation effects. He begins his discussion of heavy quark decay by reviewing data on charm and beauty lifetimes. Present data on fully leptonic and semileptonic charm decay are then reviewed. Measurements of the hadronic weak current form factors are compared to the nonperturbative QCD-based predictions of Lattice Gauge Theories. He next discusses polarization phenomena present in charmed baryon decay. Heavy Quark Effective Theory predicts that the daughter baryon will recoil from the charmed parent with nearly 100% left-handed polarization, which is in excellent agreement with present data. He concludes by discussing nonleptonic charm decay which is traditionally analyzed in a factorization framework applicable to two-body and quasi-two-body nonleptonic decays. This discussion emphasizes the important role of final state interactions in influencing both the observed decay width of various two-body final states as well as modifying the interference between interfering resonance channels which contribute to specific multibody decays. 50 refs., 77 figs.

  10. QCD in heavy quark production and decay

    International Nuclear Information System (INIS)

    Wiss, J.

    1997-01-01

    The author discusses how QCD is used to understand the physics of heavy quark production and decay dynamics. His discussion of production dynamics primarily concentrates on charm photoproduction data which are compared to perturbative QCD calculations which incorporate fragmentation effects. He begins his discussion of heavy quark decay by reviewing data on charm and beauty lifetimes. Present data on fully leptonic and semileptonic charm decay are then reviewed. Measurements of the hadronic weak current form factors are compared to the nonperturbative QCD-based predictions of Lattice Gauge Theories. He next discusses polarization phenomena present in charmed baryon decay. Heavy Quark Effective Theory predicts that the daughter baryon will recoil from the charmed parent with nearly 100% left-handed polarization, which is in excellent agreement with present data. He concludes by discussing nonleptonic charm decay which is traditionally analyzed in a factorization framework applicable to two-body and quasi-two-body nonleptonic decays. This discussion emphasizes the important role of final state interactions in influencing both the observed decay width of various two-body final states as well as modifying the interference between interfering resonance channels which contribute to specific multibody decays. 50 refs., 77 figs

  11. Quantum chaos and chiral symmetry at the QCD and QED phase transition

    International Nuclear Information System (INIS)

    Bittner, Elmar; Markum, Harald; Pullirsch, Rainer

    2001-01-01

    We investigate the eigenvalue spectrum of the staggered Dirac matrix in SU(3) gauge theory and in full QCD as well as in quenched U(1) theory. As a measure of the fluctuation properties of the eigenvalues, we consider the nearest-neighbor spacing distribution. We find that in all regions of their phase diagrams, compact lattice gauge theories have bulk spectral correlations given by random matrix theory, which is an indication for quantum chaos. In the confinement phase, the low-lying Dirac spectrum of these quantum field theories is well described by random matrix theory, exhibiting universal behavior. Related results for gauge theories with minimal coupling are now discussed also in the chirally symmetric phase

  12. Critical slowing down and error analysis in lattice QCD simulations

    Energy Technology Data Exchange (ETDEWEB)

    Schaefer, Stefan [Humboldt-Universitaet, Berlin (Germany). Inst. fuer Physik; Sommer, Rainer; Virotta, Francesco [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC

    2010-09-15

    We study the critical slowing down towards the continuum limit of lattice QCD simulations with Hybrid Monte Carlo type algorithms. In particular for the squared topological charge we find it to be very severe with an effective dynamical critical exponent of about 5 in pure gauge theory. We also consider Wilson loops which we can demonstrate to decouple from the modes which slow down the topological charge. Quenched observables are studied and a comparison to simulations of full QCD is made. In order to deal with the slow modes in the simulation, we propose a method to incorporate the information from slow observables into the error analysis of physical observables and arrive at safer error estimates. (orig.)

  13. Critical slowing down and error analysis in lattice QCD simulations

    International Nuclear Information System (INIS)

    Schaefer, Stefan; Sommer, Rainer; Virotta, Francesco

    2010-09-01

    We study the critical slowing down towards the continuum limit of lattice QCD simulations with Hybrid Monte Carlo type algorithms. In particular for the squared topological charge we find it to be very severe with an effective dynamical critical exponent of about 5 in pure gauge theory. We also consider Wilson loops which we can demonstrate to decouple from the modes which slow down the topological charge. Quenched observables are studied and a comparison to simulations of full QCD is made. In order to deal with the slow modes in the simulation, we propose a method to incorporate the information from slow observables into the error analysis of physical observables and arrive at safer error estimates. (orig.)

  14. Self-dual gauge theories

    International Nuclear Information System (INIS)

    Zet, G.

    2002-01-01

    The self-duality equations are important in gauge theories because they show the connection between gauge models with internal symmetry groups and gauge theory of gravity. They are differential equations of the first order and it is easier to investigate the solutions for different particular configurations of the gauge fields and of space-times.One of the most important property of the self-duality equations is that they imply the Yang-Mills field equations. In this paper we will prove this property for the general case of a gauge theory with compact Lie group of symmetry over a 4-dimensional space-time manifold. It is important to remark that there are 3m independent self-duality equations (of the first order) while the number of Yang-Mills equations is equal to 4m, where m is the dimension of the gauge group. Both of them have 4m unknown functions which are the gauge potentials A μ a (x), a = 1, 2, ....,m; μ = 0, 1, 2, 3. But, we have, in addition, m gauge conditions for A μ a (x), (for example Coulomb, Lorentz or axial gauge) which together with the selfduality equation constitute a system of 4m equations. The Bianchi identities for the self-dual stress tensor F μν a coincide with the Yang-Mills equations and do not imply therefore supplementary conditions. We use the axial gauge in order to obtain the self duality equations for a SU(2) gauge theory over a curved space-time. The compatibility between self-duality and Yang-Mills equations is studied and some classes of solutions are obtained. In fact, we will write the Einstein-Yang-Mills equations and we will analyse only the Yang-Mills sector. The Einstein equations can not be obtained of course from self-duality. They should be obtained if we would consider a gauge theory having P x SU(2) as symmetry group, where P is the Poincare group. More generally, a gauge theory of N-extended supersymmetry can be developed by imposing the self-duality condition. (author)

  15. Uses of Effective Field Theory in Lattice QCD

    OpenAIRE

    Kronfeld, Andreas S.

    2002-01-01

    Several physical problems in particle physics, nuclear physics, and astrophysics require information from non-perturbative QCD to gain a full understanding. In some cases the most reliable technique for quantitative results is to carry out large-scale numerical calculations in lattice gauge theory. As in any numerical technique, there are several sources of uncertainty. This chapter explains how effective field theories are used to keep them under control and, then, obtain a sensible error ba...

  16. Light hadron spectrum in 2+1 flavor full QCD by CP-PACS and JLQCD Collaborations

    International Nuclear Information System (INIS)

    Ishikawa, T.; Aoki, S.; Fukugita, M.; Hashimoto, S.; Ishikawa, K-I.; Ishizuka, N.; Iwasaki, Y.; Kanaya, K.; Kaneko, T.; Kuramashi, Y.; Okawa, M.; Onogi, T.; Taniguchi, N.; Tsutsui, N.; Ukawa, A.; Yoshie, T.

    2005-01-01

    CP-PACS and JLQCD Collaborations are carrying out a joint project of the 2+1 flavor full QCD with the RG-improved gauge action and the non-perturbatively O(a)-improved Wilson quark action. This simulation removes quenching effects of all three light quarks, which is the last major uncertainty in lattice QCD. In this report we present our results for the light meson spectrum and quark masses on a 20 3 x40 lattice at the lattice spacing a∼0.10 fm

  17. Light-Front QCD

    Energy Technology Data Exchange (ETDEWEB)

    Brodsky, S.

    2004-11-30

    In these lectures, I survey a number of applications of light-front methods to hadron and nuclear physics phenomenology and dynamics, including light-front statistical physics. Light-front Fock-state wavefunctions provide a frame-independent representation of hadrons in terms of their fundamental quark and gluon degrees of freedom. Nonperturbative methods for computing LFWFs in QCD are discussed, including string/gauge duality which predicts the power-law fall-off at high momentum transfer of light-front Fock-state hadronic wavefunctions with an arbitrary number of constituents and orbital angular momentum. The AdS/CFT correspondence has important implications for hadron phenomenology in the conformal limit, including an all-orders derivation of counting rules for exclusive processes. One can also compute the hadronic spectrum of near-conformal QCD assuming a truncated AdS/CFT space. Given the LFWFs, one can compute form factors, heavy hadron decay amplitudes, hadron distribution amplitudes, and the generalized parton distributions underlying deeply virtual Compton scattering. The quantum fluctuations represented by the light-front Fock expansion leads to novel QCD phenomena such as color transparency, intrinsic heavy quark distributions, diffractive dissociation, and hidden-color components of nuclear wavefunctions. A new test of hidden color in deuteron photodisintegration is proposed. The origin of leading-twist phenomena such as the diffractive component of deep inelastic scattering, single-spin asymmetries, nuclear shadowing and antishadowing is also discussed; these phenomena cannot be described by light-front wavefunctions of the target computed in isolation. Part of the anomalous NuTeV results for the weak mixing angle {theta}{sub W} could be due to the non-universality of nuclear antishadowing for charged and neutral currents.

  18. Two-loop master integrals for the leading QCD corrections to the Higgs coupling to a W pair and to the triple gauge couplings ZWW and γ{sup ∗}WW

    Energy Technology Data Exchange (ETDEWEB)

    Vita, Stefano Di [DESY,Notkestraße 85, D-22607 Hamburg (Germany); Mastrolia, Pierpaolo; Primo, Amedeo [Dipartimento di Fisica ed Astronomia, Università di Padova,Via Marzolo 8, 35131 Padova (Italy); INFN - Sezione di Padova,Via Marzolo 8, 35131 Padova (Italy); Schubert, Ulrich [High Energy Physics Division, Argonne National Laboratory,Argonne, IL 60439 (United States)

    2017-04-03

    We compute the two-loop master integrals required for the leading QCD corrections to the interaction vertex of a massive neutral boson X{sup 0}, e.g. H,Z or γ{sup ∗}, with a pair of W bosons, mediated by a SU(2){sub L} quark doublet composed of one massive and one massless flavor. All the external legs are allowed to have arbitrary invariant masses. The Magnus exponential is employed to identify a set of master integrals that, around d=4 space-time dimensions, obey a canonical system of differential equations. The canonical master integrals are given as a Taylor series in ϵ=(4−d)/2, up to order four, with coefficients written as combination of Goncharov polylogarithms, respectively up to weight four. In the context of the Standard Model, our results are relevant for the mixed EW-QCD corrections to the Higgs decay to a W pair, as well as to the production channels obtained by crossing, and to the triple gauge boson vertices ZWW and γ{sup ∗}WW.

  19. An N=2 gauge theory and its supergravity dual

    CERN Document Server

    Brandhuber, A

    2000-01-01

    We study flows on the scalar manifold of N=8 gauged supergravity in five dimensions which are dual to certain mass deformations of N=4 super Yang-Mill theory. In particular, we consider a perturbation of the gauge theory by a mass term for the adjoint hyper-multiplet, giving rise to an N=2 theory. The exact solution of the 5-dim gauged supergravity equations of motion is found and the metric is uplifted to a ten-dimensional background of type-IIB supergravity. Using these geometric data and the AdS/CFT correspondence we analyze the spectra of certain operators as well as Wilson loops on the dual gauge theory side. The physical flows are parametrized by a single non-positive constant and describe part of the Coulomb branch of the N=2 theory at strong coupling.

  20. Reality of the fundamental topological structure in the QCD vacuum

    International Nuclear Information System (INIS)

    Alexandru, Andrei; Horvath, Ivan; Zhang Jianbo

    2005-01-01

    Long-range order of a specific kind has recently been found directly in configurations dominating the regularized QCD path integral. In particular, a low-dimensional global structure was identified in typical space-time distributions of topological charge defined via the overlap Dirac matrix. The presence of the order has been concluded from the fact that the structure disappears after random permutation of position coordinates in measured densities. Here we complete the argument for the reality of this structure (namely the conjecture that its existence is a consequence of QCD dynamics and not an artifact of the overlap-based definition of lattice topological field) by showing that the structure ceases to exist after randomizing the space-time coordinates of the underlying gauge field. This implies that the long-range order present in the overlap-based topological density is indeed a manifestation of the QCD vacuum, and that the notion of the fundamental structure (structure involving relevant features at all scales) is viable

  1. Higher twist effects in QCD description of light meson exclusive formfactors

    International Nuclear Information System (INIS)

    Gorskij, A.S.

    1987-01-01

    The general approach to a quantitative description of higher twist effects in hard exclusive processes in QCD is proposed. The consistent calculations in coordinate space and the choice of special gauges for quantum and classical gluon fields are essential ingradients of this method. The self consistent system of twist three wave functions for π-meson has been built

  2. QCD condensates in ADS/QCD

    DEFF Research Database (Denmark)

    Bechi, Jacopo

    2009-01-01

    This paper focuses on some issues about condensates and renormalization in AdS/QCD models. In particular we consider the consistency of the AdS/QCD approach for scale dependent quantities as the chiral condensate questioned in some recent papers and the 4D meaning of the 5D cosmological constant...... in a model in which the QCD is dual to a 5D gravity theory. We will be able to give some arguments that the cosmological constant is related to the QCD gluon condensate....

  3. Conformal gauge-Yukawa theories away from four dimensions

    Energy Technology Data Exchange (ETDEWEB)

    Codello, Alessandro; Langæble, Kasper [CP-Origins, University of Southern Denmark,Campusvej 55, Odense, DK-5230 (Denmark); Litim, Daniel F. [Department of Physics and Astronomy, University of Sussex,Brighton, BN1 9QH (United Kingdom); Sannino, Francesco [CP-Origins, University of Southern Denmark,Campusvej 55, Odense, DK-5230 (Denmark); Danish Institute for Advanced Study, Danish IAS, University of Southern Denmark,Campusvej 55, Odense, DK-5230 (Denmark)

    2016-07-22

    We present the phase diagram and associated fixed points for a wide class of Gauge-Yukawa theories in d=4+ϵ dimensions. The theories we investigate involve non-abelian gauge fields, fermions and scalars in the Veneziano-Witten limit. The analysis is performed in steps, we start with QCD{sub d} and then we add Yukawa interactions and scalars which we study at next-to- and next-to-next-to-leading order. Interacting infrared fixed points naturally emerge in dimensions lower than four while ultraviolet ones appear above four. We also analyse the stability of the scalar potential for the discovered fixed points. We argue for a very rich phase diagram in three dimensions while in dimensions higher than four certain Gauge-Yukawa theories are ultraviolet complete because of the emergence of an asymptotically safe fixed point.

  4. Closed String Tachyons, AdS/CFT, and QCD

    International Nuclear Information System (INIS)

    Silverstein, Eva M

    2001-01-01

    We find that tachyonic orbifold examples of AdS/CFT have corresponding instabilities at small radius, and can decay to more generic gauge theories. We do this by computing a destabilizing Coleman-Weinberg effective potential for twisted operators of the corresponding quiver gauge theories, generalizing calculations of Tseytlin and Zarembo and interpreting them in terms of the large-N behavior of twisted-sector modes. The dynamically generated potential involves double-trace operators, which affect large-N correlators involving twisted fields but not those involving only untwisted fields, in line with large-N inheritance arguments. We point out a simple reason that no such small radius instability exists in gauge theories arising from freely acting orbifolds, which are tachyon-free at large radius. When an instability is present, twisted gauge theory operators with the quantum numbers of the large-radius tachyons acquire VEVs, leaving a gauge theory with fewer degrees of freedom in the infrared, analogous to but less extreme than ''decays to nothing'' studied in other systems with broken supersymmetry. In some cases one is left with pure glue QCD plus decoupled matter and U(1) factors in the IR, which we thus conjecture is described by the corresponding (possibly strongly coupled) endpoint of tachyon condensation in the M/String-theory dual

  5. One-instanton calculations in N=2 supersymmetric gauge theories

    International Nuclear Information System (INIS)

    Ito, Katsushi

    1998-01-01

    We study the low-energy effective action of N=2 supersymmetric gauge theories in the Coulomb branch. Using microscopic instanton calculus, we compute the one-instanton contribution to the pre potential for N=2 supersymmetric SU(N c ) Yang-Mills theory. We show that the microscopic result agrees with the exact solution. (Author). 23 refs

  6. Matter fields near quantum critical point in (2+1)-dimensional U(1) gauge theory

    International Nuclear Information System (INIS)

    Liu Guozhu; Li Wei; Cheng Geng

    2010-01-01

    We study chiral phase transition and confinement of matter fields in (2+1)-dimensional U(1) gauge theory of massless Dirac fermions and scalar bosons. The vanishing scalar boson mass, r=0, defines a quantum critical point between the Higgs phase and the Coulomb phase. We consider only the critical point r=0 and the Coulomb phase with r>0. The Dirac fermion acquires a dynamical mass when its flavor is less than certain critical value N f c , which depends quantitatively on the flavor N b and the scalar boson mass r. When N f f c , the matter fields carrying internal gauge charge are all confined if r≠0 but are deconfined at the quantum critical point r=0. The system has distinct low-energy elementary excitations at the critical point r=0 and in the Coulomb phase with r≠0. We calculate the specific heat and susceptibility of the system at r=0 and r≠0, which can help to detect the quantum critical point and to judge whether dynamical fermion mass generation takes place.

  7. D-branes and coherent topological charge structure in QCD

    Science.gov (United States)

    Thacker, Hank

    2006-12-01

    Monte Carlo studies of pure glue SU(3) gauge theory using the overlap-based topological charge operator have revealed a laminar structure in the QCD vacuum consisting of extended, thin, co- herent, locally 3-dimensional sheets of topological charge embedded in 4D space, with opposite sign sheets interleaved. Studies of localization properties of Dirac eigenmodes have also shown evidence for the delocalization of low-lying modes on effectively 3-dimensional surfaces. In this talk, I review some theoretical ideas which suggest the possibility of 3-dimensionally coherent topological charge structure in 4-dimensional gauge theory and provide a possible interpretation of the observed structure. I begin with Luscher's "Wilson bag" integral over the 3-index Chern- Simons tensor. The analogy with a Wilson loop as a charged world line in 2-dimensional CP N-1 sigma models suggests that the Wilson bag surface represents the world volume of a physical membrane. The large-N chiral Lagrangian arguments of Witten also indicate the existence of multiple "k-vacuum" states with discontinuous transitions between k-vacua at θ = odd multi- ples of π. The domain walls between these vacua have the properties of a Wilson bag surface. Finally, I review the AdS/CFT duality view of θ dependence in QCD. The dual realtionship be- tween topological charge in gauge theory and Ramond-Ramond charge in type IIA string theory suggests that the coherent topological charge sheets observed on the lattice are the holographic image of wrapped D6 branes.

  8. Electromagnetic potentials without gauge transformations

    International Nuclear Information System (INIS)

    Chubykalo, A; Espinoza, A; Alvarado Flores, R

    2011-01-01

    In this paper, we show that the use of the Helmholtz theorem enables the derivation of uniquely determined electromagnetic potentials without the necessity of using gauge transformation. We show that the electromagnetic field comprises two components, one of which is characterized by instantaneous action at a distance, whereas the other propagates in retarded form with the velocity of light. In our attempt to show the superiority of the new proposed method to the standard one, we argue that the action-at-a-distance components cannot be considered as a drawback of our method, because the recommended procedure for eliminating the action at a distance in the Coulomb gauge leads to theoretical subtleties that allow us to say that the needed gauge transformation is not guaranteed. One of the theoretical consequences of this new definition is that, in addition to the electric E and magnetic B fields, the electromagnetic potentials are real physical quantities. We show that this property of the electromagnetic potentials in quantum mechanics is also a property of the electromagnetic potentials in classical electrodynamics.

  9. Virtual Compton Scattering off a Spinless Target in the AdS/QCD correspondence

    Energy Technology Data Exchange (ETDEWEB)

    Wallon, Samuel [Laboratoire de Physique Theorique d' Orsay - LPT, Bat. 210, Univ. Paris-Sud 11, 91405 Orsay Cedex (France); Marquet, Cyrille [IPhT - Institut de Physique Theorique, Orme des Merisiers bat. 774, PC 136, CEA/DSM/IPhT, CEA/Saclay, F-91191 Gif-sur-Yvette Cedex (France); Roiesnel, Claude [Centre de Physique Theorique - CPHT, UMR 7644, Ecole Polytechnique, Bat. 6, RDC, F91128 Palaiseau Cedex (France)

    2010-07-01

    We study the doubly virtual Compton scattering off a spinless target {gamma}* P {yields} {gamma}* P' within the Anti-de Sitter(AdS)/QCD formalism. We find that the general structure allowed by the Lorentz invariance and gauge invariance of the Compton amplitude is not easily reproduced with the standard recipes of the AdS/QCD correspondence. In the soft-photon regime, where the semi-classical approximation is supposed to apply best, we show that the measurements of the electric and magnetic polarizabilities of a target like the charged pion in real Compton scattering, can already serve as stringent tests. (author)

  10. The strong coupling constant of QCD with four flavors

    Energy Technology Data Exchange (ETDEWEB)

    Tekin, Fatih

    2010-11-01

    In this thesis we study the theory of strong interaction Quantum Chromodynamics on a space-time lattice (lattice QCD) with four flavors of dynamical fermions by numerical simulations. In the early days of lattice QCD, only pure gauge field simulations were accessible to the computational facilities and the effects of quark polarization were neglected. The so-called fermion determinant in the path integral was set to one (quenched approximation). The reason for this approximation was mainly the limitation of computational power because the inclusion of the fermion determinant required an enormous numerical effort. However, for full QCD simulations the virtual quark loops had to be taken into account and the development of new machines and new algorithmic techniques made the so-called dynamical simulations with at least two flavors possible. In recent years, different collaborations studied lattice QCD with dynamical fermions. In our project we study lattice QCD with four degenerated flavors of O(a) improved Wilson quarks in the Schroedinger functional scheme and calculate the energy dependence of the strong coupling constant. For this purpose, we determine the O(a) improvement coefficient c{sub sw} with four flavors and use this result to calculate the step scaling function of QCD with four flavors which describes the scale evolution of the running coupling. Using a recursive finite-size technique, the {lambda} parameter is determined in units of a technical scale L{sub max} which is an unambiguously defined length in the hadronic regime. The coupling {alpha}{sub SF} of QCD in the so-called Schroedinger functional scheme is calculated over a wide range of energies non-perturbatively and compared with 2-loop and 3-loop perturbation theory as well as with the non-perturbative result for only two flavors. (orig.)

  11. The strong coupling constant of QCD with four flavors

    International Nuclear Information System (INIS)

    Tekin, Fatih

    2010-01-01

    In this thesis we study the theory of strong interaction Quantum Chromodynamics on a space-time lattice (lattice QCD) with four flavors of dynamical fermions by numerical simulations. In the early days of lattice QCD, only pure gauge field simulations were accessible to the computational facilities and the effects of quark polarization were neglected. The so-called fermion determinant in the path integral was set to one (quenched approximation). The reason for this approximation was mainly the limitation of computational power because the inclusion of the fermion determinant required an enormous numerical effort. However, for full QCD simulations the virtual quark loops had to be taken into account and the development of new machines and new algorithmic techniques made the so-called dynamical simulations with at least two flavors possible. In recent years, different collaborations studied lattice QCD with dynamical fermions. In our project we study lattice QCD with four degenerated flavors of O(a) improved Wilson quarks in the Schroedinger functional scheme and calculate the energy dependence of the strong coupling constant. For this purpose, we determine the O(a) improvement coefficient c sw with four flavors and use this result to calculate the step scaling function of QCD with four flavors which describes the scale evolution of the running coupling. Using a recursive finite-size technique, the Λ parameter is determined in units of a technical scale L max which is an unambiguously defined length in the hadronic regime. The coupling α SF of QCD in the so-called Schroedinger functional scheme is calculated over a wide range of energies non-perturbatively and compared with 2-loop and 3-loop perturbation theory as well as with the non-perturbative result for only two flavors. (orig.)

  12. A quantum liquid model for the QCD vacuum

    International Nuclear Information System (INIS)

    Nielsen, H.B.; Olesen, P.

    1979-06-01

    It is shown that domains are formed in a homogeneous SU(2) color magnetic field. Due to quantum fluctuations the domains have fluid properties. It is then argued that quantum mechanically superpositions of such domains must be considered. The resulting state is gauge and rotational invariant, in spite of the fact that the original color magnetic field breaks these invariances. It is pointed out that in the model for the QCD vacuum color magnetic monopoles are not confined. (Auth.)

  13. On running couplings in gauge theories from type-IIB supergravity

    CERN Document Server

    Kehagias, A A

    1999-01-01

    We construct an explicit solution of type-IIB supergravity describing the strong coupling regime of a non-supersymmetric gauge theory. The latter has a running coupling with an ultraviolet stable fixed point corresponding to the N=4 SU(N) super-Yang-Mills theory at large N. The running coupling has a power law behaviour, argued to be universal, that is consistent with holography. Around the critical point, our solution defines an asymptotic expansion for the gauge coupling beta-function. We also calculate the first correction to the Coulombic quark-antiquark potential.

  14. Vacuum structure and QCD

    International Nuclear Information System (INIS)

    Gross, D.

    1979-01-01

    An overview of QCD is given, and some of the dynamical issues that arise in attempts to solve this theory are discussed. In particular, attention is focused on the problems that appear in attempts to discuss the structure of low-lying hadrons, e.g. nucleons, on the basis of a color gauge theory of quarks. The picture of hadronic structure developed by Callan, Dashen, and Gross is reviewed; this picture maintains that it presents the qualitative features of hadronic structure emerging in a direct way from first principles. Finally, the relevance of the emerging understanding of the structure of hadrons to the question of what hadronic matter (nuclear or quark matter) might look like at high densities is discussed

  15. RIKEN WINTER SCHOOL: STRUCTURE OF HADRONS - INTRODUCTION TO QCD HARD PROCESSES. PROCEEDINGS OF RIKEN BNL RESEARCH CENTER WORKSHOP, DECEMBER 9-12, 1998

    International Nuclear Information System (INIS)

    Saito, N.

    1999-01-01

    In this lecture I give a pedagogical introduction to the Perturbative QCD to understand the short-distance dynamics of the strong interaction. Starting with fundamental concepts such as the color degree of freedom of QCD, non-abelian gauge field theory, renormalization group equation etc., I explain a basic idea of the perturbative QCD and apply this idea to the e + e - processes and the structure functions. The notion of mass singularity and the necessity of its factorization is discussed in some detail

  16. Hadron spectrum in quenched lattice QCD and quark potential models

    International Nuclear Information System (INIS)

    Iwasaki, Y.; Yoshie, T.

    1989-01-01

    We show that the quenched lattice QCD gives a hadron spectrum which remarkably agrees with that of quark potential models for quark mass m q ≥ m strange , even when one uses the standard one-plaquette gauge action. This is contrary to what is stated in the literature. We clarify the reason of the discrepancy, paying close attention to systematic errors in numerical calculations. (orig.)

  17. Another higher order Langevin algorithm for QCD

    International Nuclear Information System (INIS)

    Kronfeld, A.S.

    1986-01-01

    This note provides an algorithm for integrating the Langevin equation which is second order. It introduces a term into the drift force which is a product of the Gaussian noise and a second derivative of the action. The specific application presented here is for nonabelian gauge theories interacting with fermions, e.g. QCD, for which it requires less memory than the Runge-Kutta algorithm of the same order. The memory and computational requirements of Euler, Runge-Kutta, and the present algorithm are compared. (orig.)

  18. Critical slowing down and error analysis in lattice QCD simulations

    Energy Technology Data Exchange (ETDEWEB)

    Virotta, Francesco

    2012-02-21

    In this work we investigate the critical slowing down of lattice QCD simulations. We perform a preliminary study in the quenched approximation where we find that our estimate of the exponential auto-correlation time scales as {tau}{sub exp}(a){proportional_to}a{sup -5}, where a is the lattice spacing. In unquenched simulations with O(a) improved Wilson fermions we do not obtain a scaling law but find results compatible with the behavior that we find in the pure gauge theory. The discussion is supported by a large set of ensembles both in pure gauge and in the theory with two degenerate sea quarks. We have moreover investigated the effect of slow algorithmic modes in the error analysis of the expectation value of typical lattice QCD observables (hadronic matrix elements and masses). In the context of simulations affected by slow modes we propose and test a method to obtain reliable estimates of statistical errors. The method is supposed to help in the typical algorithmic setup of lattice QCD, namely when the total statistics collected is of O(10){tau}{sub exp}. This is the typical case when simulating close to the continuum limit where the computational costs for producing two independent data points can be extremely large. We finally discuss the scale setting in N{sub f}=2 simulations using the Kaon decay constant f{sub K} as physical input. The method is explained together with a thorough discussion of the error analysis employed. A description of the publicly available code used for the error analysis is included.

  19. Critical slowing down and error analysis in lattice QCD simulations

    International Nuclear Information System (INIS)

    Virotta, Francesco

    2012-01-01

    In this work we investigate the critical slowing down of lattice QCD simulations. We perform a preliminary study in the quenched approximation where we find that our estimate of the exponential auto-correlation time scales as τ exp (a)∝a -5 , where a is the lattice spacing. In unquenched simulations with O(a) improved Wilson fermions we do not obtain a scaling law but find results compatible with the behavior that we find in the pure gauge theory. The discussion is supported by a large set of ensembles both in pure gauge and in the theory with two degenerate sea quarks. We have moreover investigated the effect of slow algorithmic modes in the error analysis of the expectation value of typical lattice QCD observables (hadronic matrix elements and masses). In the context of simulations affected by slow modes we propose and test a method to obtain reliable estimates of statistical errors. The method is supposed to help in the typical algorithmic setup of lattice QCD, namely when the total statistics collected is of O(10)τ exp . This is the typical case when simulating close to the continuum limit where the computational costs for producing two independent data points can be extremely large. We finally discuss the scale setting in N f =2 simulations using the Kaon decay constant f K as physical input. The method is explained together with a thorough discussion of the error analysis employed. A description of the publicly available code used for the error analysis is included.

  20. Hadron spectrum in quenched lattice QCD and distribution of zero modes

    International Nuclear Information System (INIS)

    Iwasaki, Yoichi

    1989-01-01

    I report the results of the calculation of the hadron spectrum with the standard one-plaquette gauge action on a 16 3 x48 lattice at β=5.85 in the quenched lattice QCD. The result remarkably agrees with that of quark potential models for the case where the quark mass is equal to or is larger than the strange quark mass, even when one uses the standard one-plaquette gauge action. This is contrary to what is stated in the literature. We clarify the reason of the discrepancy, paying close attention to systematic errors in numerical calculations. Further, I show the distribution of zero modes of quark matrix, both in the cases of a RG improved gauge action and the standard action, and discuss the difference between the two cases. (orig.)

  1. arXiv Mass-improvement of the vector current in three-flavor QCD

    CERN Document Server

    Fritzsch, Patrick

    2018-06-04

    We determine two improvement coefficients which are relevant to cancel mass-dependent cutoff effects in correlation functions with operator insertions of the non-singlet local QCD vector current. This determination is based on degenerate three-flavor QCD simulations of non-perturbatively O(a) improved Wilson fermions with tree-level improved gauge action. Employing a very robust strategy that has been pioneered in the quenched approximation leads to an accurate estimate of a counterterm cancelling dynamical quark cutoff effects linear in the trace of the quark mass matrix. To our knowledge this is the first time that such an effect has been determined systematically with large significance.

  2. 4d N=2 theories with disconnected gauge groups

    Energy Technology Data Exchange (ETDEWEB)

    Argyres, Philip C.; Martone, Mario [Physics Department, University of Cincinnati,PO Box 210011, Cincinnati OH 45221 (United States)

    2017-03-28

    In this paper we present a beautifully consistent web of evidence for the existence of interacting 4d rank-1 N=2 SCFTs obtained from gauging discrete subgroups of global symmetries of other existing 4d rank-1 N=2 SCFTs. The global symmetries that can be gauged involve a non-trivial combination of discrete subgroups of the U(1){sub R}, low-energy EM duality group SL(2,ℤ), and the outer automorphism group of the flavor symmetry algebra, Out(F). The theories that we construct are remarkable in many ways: (i) two of them have exceptional F{sub 4} and G{sub 2} flavor groups; (ii) they substantially complete the picture of the landscape of rank-1 N=2 SCFTs as they realize all but one of the remaining consistent rank-1 Seiberg-Witten geometries that we previously constructed but were not associated to known SCFTs; and (iii) some of them have enlarged N=3 SUSY, and have not been previously constructed. They are also examples of SCFTs which violate the Shapere-Tachikawa relation between the conformal central charges and the scaling dimension of the Coulomb branch vev. We propose a modification of the formulas computing these central charges from the topologically twisted Coulomb branch partition function which correctly compute them for discretely gauged theories.

  3. Infra-red divergences and Regge behaviour in QCD

    International Nuclear Information System (INIS)

    Jaroszewicz, T.

    1980-01-01

    We analyze high energy behaviour of multi-gluon exchange amplitudes in the leading-lns approximation in perturbation theory. Working in the Coulomb gauge and employing Ward identities we derive an integral equation for the n-gluon system in the exchange channel. We find that the Regge behaviour is associated with exponentiation of leading infrared divergences, and the position of the j-plane singularities is determined by the colour quantum numbers of the exchanged system. (author)

  4. More about orbitally excited hadrons from lattice QCD

    International Nuclear Information System (INIS)

    DeGrand, T.A.; Hecht, M.W.

    1992-01-01

    This is the second of two papers describing the calculation of spectroscopy for orbitally excited states from lattice simulations of quantum chromodynamics. New features include higher statistics for P-wave systems and first results for the spectroscopy of D-wave mesons and baryons, for relatively heavy-quark masses. We parametrize the Coulomb gauge wave functions for P- and D-wave systems and compare them to those of their corresponding S-wave states

  5. A non-technical introduction to confinement and N = 2 globally supersymmetric Yang-Mills gauge theories

    International Nuclear Information System (INIS)

    Fucito, F.

    1997-01-01

    The aim of this talk is to give a brief introduction to the problem of confinement in QCD and N = 2 globally supersymmetric Yang-Mills gauge theories (SYM). While avoiding technicalities as much as possible I will try to emphasize the physical ideas which lie behind the picture of confinement as a consequence of the vacua of QCD to be a dual superconductor. Finally I review the implementation of this picture in the framework of N = 2 SYM. (author)

  6. Direct gauge mediation of uplifted metastable supersymmetry breaking in supergravity

    International Nuclear Information System (INIS)

    Maru, Nobuhito

    2010-01-01

    We propose a direct gauge mediation model based on an uplifted metastable supersymmetry (SUSY) breaking coupled to supergravity. A constant superpotential plays an essential role to fix the moduli as well as breaking SUSY and R symmetry and the cancellation of the cosmological constant. Gaugino masses are generated at leading order of SUSY breaking scale, and comparable to the sfermion masses as in the ordinary gauge mediation. The Landau pole problem for QCD coupling can be easily solved since more than half of messengers become superheavy, which are heavier than the grand unified theory (GUT) scale.

  7. Full NLO massive gauge boson pair production at the LHC

    CERN Document Server

    Baglio, Julien; Weber, Marcus M

    2013-01-01

    Electroweak gauge boson pair production is a very important process at the LHC as it probes the non-abelian structure of electroweak interactions and is a background process for many searches. We present full next-to-leading order predictions for the production cross sections and distributions of on-shell massive gauge boson pair production in the Standard Model, including both QCD and electroweak corrections. The hierarchy between the ZZ, WW and WZ channels, observed in the transverse momentum distributions, will be analyzed. We will also present a comparison with experimental data for the total cross sections including a study of the theoretical uncertainties.

  8. Pion structure from lattice QCD

    Energy Technology Data Exchange (ETDEWEB)

    Javadi Motaghi, Narjes

    2015-05-12

    In this thesis we use lattice QCD to compute the second Mellin moments of pion generalized parton distributions and pion electromagnetic form factors. For our calculations we are able to analyze a large set of gauge configurations with 2 dynamical flavours using non-perturbatively the improved Wilson-Sheikholeslami-Wohlert fermionic action pion masses ranging down to 151 MeV. By employing improved smearing we were able to suppress excited state contamination. However, our data in the physical quark mass limit show that some excited state contamination remains. We show the non-zero sink momentum is optimal for the computation of the electromagnetic form factors and generalized form factors at finite momenta.

  9. A gauge-invariant reorganization of thermal gauge theory

    International Nuclear Information System (INIS)

    Su, Nan

    2010-01-01

    This dissertation is devoted to the study of thermodynamics for quantum gauge theories. The poor convergence of quantum field theory at finite temperature has been the main obstacle in the practical applications of thermal QCD for decades. In this dissertation I apply hard-thermal-loop perturbation theory, which is a gauge-invariant reorganization of the conventional perturbative expansion for quantum gauge theories to the thermodynamics of QED and Yang-Mills theory to three-loop order. For the Abelian case, I present a calculation of the free energy of a hot gas of electrons and photons by expanding in a power series in m D /T, m f /T and e 2 , where m D and m f are the photon and electron thermal masses, respectively, and e is the coupling constant. I demonstrate that the hard-thermal-loop perturbation reorganization improves the convergence of the successive approximations to the QED free energy at large coupling, e ∝ 2. For the non-Abelian case, I present a calculation of the free energy of a hot gas of gluons by expanding in a power series in m D /T and g 2 , where m D is the gluon thermal mass and g is the coupling constant. I show that at three-loop order hard-thermal-loop perturbation theory is compatible with lattice results for the pressure, energy density, and entropy down to temperatures T ∝ 2 - 3 T c . The results suggest that HTLpt provides a systematic framework that can be used to calculate static and dynamic quantities for temperatures relevant at LHC. (orig.)

  10. An asymptotic solution of large-N QCD

    Directory of Open Access Journals (Sweden)

    Bochicchio Marco

    2014-01-01

    Full Text Available We find an asymptotic solution for two-, three- and multi-point correlators of local gauge-invariant operators, in a lower-spin sector of massless large-N QCD, in terms of glueball and meson propagators, in such a way that the solution is asymptotic in the ultraviolet to renormalization-group improved perturbation theory, by means of a new purely field-theoretical technique that we call the asymptotically-free bootstrap, based on a recently-proved asymptotic structure theorem for two-point correlators. The asymptotically-free bootstrap provides as well asymptotic S-matrix amplitudes in terms of glueball and meson propagators. Remarkably, the asymptotic S-matrix depends only on the unknown particle spectrum, but not on the anomalous dimensions, as a consequence of the LS Z reduction formulae. Very many physics consequences follow, both practically and theoretically. In fact, the asymptotic solution sets the strongest constraints on any actual solution of large-N QCD, and in particular on any string solution.

  11. Performance tests of the Kramers equation and boson algorithms for simulations of QCD

    International Nuclear Information System (INIS)

    Jansen, K.; Liu Chuan; Jegerlehner, B.

    1995-12-01

    We present a performance comparison of the Kramers equation and the boson algorithms for simulations of QCD with two flavors of dynamical Wilson fermions and gauge group SU(2). Results are obtained on 6 3 12, 8 3 12 and 16 4 lattices. In both algorithms a number of optimizations are installed. (orig.)

  12. Light-Front Quantization of Gauge Theories

    Energy Technology Data Exchange (ETDEWEB)

    Brodsky, Stanley J.

    2003-03-25

    Light-front wavefunctions provide a frame-independent representation of hadrons in terms of their physical quark and gluon degrees of freedom. The light-front Hamiltonian formalism provides new nonperturbative methods for obtaining the QCD spectrum and eigensolutions, including resolvant methods, variational techniques, and discretized light-front quantization. A new method for quantizing gauge theories in light-cone gauge using Dirac brackets to implement constraints is presented. In the case of the electroweak theory, this method of light-front quantization leads to a unitary and renormalizable theory of massive gauge particles, automatically incorporating the Lorentz and 't Hooft conditions as well as the Goldstone boson equivalence theorem. Spontaneous symmetry breaking is represented by the appearance of zero modes of the Higgs field leaving the light-front vacuum equal to the perturbative vacuum. I also discuss an ''event amplitude generator'' for automatically computing renormalized amplitudes in perturbation theory. The importance of final-state interactions for the interpretation of diffraction, shadowing, and single-spin asymmetries in inclusive reactions such as deep inelastic lepton-hadron scattering is emphasized.

  13. Light-Front Quantization of Gauge Theories

    Energy Technology Data Exchange (ETDEWEB)

    Brodskey, Stanley

    2002-12-01

    Light-front wavefunctions provide a frame-independent representation of hadrons in terms of their physical quark and gluon degrees of freedom. The light-front Hamiltonian formalism provides new nonperturbative methods for obtaining the QCD spectrum and eigensolutions, including resolvant methods, variational techniques, and discretized light-front quantization. A new method for quantizing gauge theories in light-cone gauge using Dirac brackets to implement constraints is presented. In the case of the electroweak theory, this method of light-front quantization leads to a unitary and renormalizable theory of massive gauge particles, automatically incorporating the Lorentz and 't Hooft conditions as well as the Goldstone boson equivalence theorem. Spontaneous symmetry breaking is represented by the appearance of zero modes of the Higgs field leaving the light-front vacuum equal to the perturbative vacuum. I also discuss an ''event amplitude generator'' for automatically computing renormalized amplitudes in perturbation theory. The importance of final-state interactions for the interpretation of diffraction, shadowing, and single-spin asymmetries in inclusive reactions such as deep inelastic lepton-hadron scattering is emphasized.

  14. Hyperon-Nulceon Scattering from Fully-Dynamical Lattice QCD

    Energy Technology Data Exchange (ETDEWEB)

    Silas Beane; Paulo Bedaque; Thomas Luu; Konstantinos Orginos; Elizabetta Pallante; Assumpta Parreno; Martin Savage

    2007-10-01

    We present results of the first fully-dynamical lattice QCD determination of hyperon-nucleon scattering. One s-wave phase shift was determined for n{Lambda} scattering in both spin-channels at pion masses of 350, 490, and 590 MeV, and for n{Sigma}^- scattering in both spin channels at pion masses of 490, and 590 MeV. The calculations were performed with domain-wall valence quarks on dynamical, staggered gauge configurations with a lattice spacing of b ~0.125 fm.

  15. 13. international QCD conference (QCD 06)

    International Nuclear Information System (INIS)

    2006-01-01

    This conference was organized around 5 sessions: 1) quantum chromodynamics (QCD) at colliders, 2) CP-violation, Kaon decays and Chiral symmetry, 3) perturbative QCD, 4) physics of light and heavy hadrons, 5) confinement, thermodynamics QCD and axion searches. This document gathers only the slides of the presentations

  16. 13. international QCD conference (QCD 06)

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2006-07-01

    This conference was organized around 5 sessions: 1) quantum chromodynamics (QCD) at colliders, 2) CP-violation, Kaon decays and Chiral symmetry, 3) perturbative QCD, 4) physics of light and heavy hadrons, 5) confinement, thermodynamics QCD and axion searches. This document gathers only the slides of the presentations.

  17. Baryon bags in strong coupling QCD

    Science.gov (United States)

    Gattringer, Christof

    2018-04-01

    We discuss lattice QCD with one flavor of staggered fermions and show that in the path integral the baryon contributions can be fully separated from quark and diquark contributions. The baryonic degrees of freedom (d.o.f.) are independent of the gauge field, and the corresponding free fermion action describes the baryons through the joint propagation of three quarks. The nonbaryonic dynamics is described by quark and diquark terms that couple to the gauge field. When evaluating the quark and diquark contributions in the strong coupling limit, the partition function completely factorizes into baryon bags and a complementary domain. Baryon bags are regions in space-time where the dynamics is described by a single free fermion made out of three quarks propagating coherently as a baryon. Outside the baryon bags, the relevant d.o.f. are monomers and dimers for quarks and diquarks. The partition sum is a sum over all baryon bag configurations, and for each bag, a free fermion determinant appears as a weight factor.

  18. Setting the renormalization scale in QCD: The principle of maximum conformality

    DEFF Research Database (Denmark)

    Brodsky, S. J.; Di Giustino, L.

    2012-01-01

    A key problem in making precise perturbative QCD predictions is the uncertainty in determining the renormalization scale mu of the running coupling alpha(s)(mu(2)). The purpose of the running coupling in any gauge theory is to sum all terms involving the beta function; in fact, when the renormali......A key problem in making precise perturbative QCD predictions is the uncertainty in determining the renormalization scale mu of the running coupling alpha(s)(mu(2)). The purpose of the running coupling in any gauge theory is to sum all terms involving the beta function; in fact, when...... the renormalization scale is set properly, all nonconformal beta not equal 0 terms in a perturbative expansion arising from renormalization are summed into the running coupling. The remaining terms in the perturbative series are then identical to that of a conformal theory; i.e., the corresponding theory with beta...... = 0. The resulting scale-fixed predictions using the principle of maximum conformality (PMC) are independent of the choice of renormalization scheme-a key requirement of renormalization group invariance. The results avoid renormalon resummation and agree with QED scale setting in the Abelian limit...

  19. A new scheme for NMSSM in gauge mediation

    International Nuclear Information System (INIS)

    Asano, Masaki; Nakai, Yuichiro; Yokozaki, Norimi

    2016-01-01

    We propose a new framework for the next-to-minimal supersymmetric standard model (NMSSM) in gauge mediation, where in general the correct electroweak symmetry breaking (EWSB) is difficult to be explained. The difficulty is caused by the absence of a soft supersymmetry (SUSY) breaking mass for the NMSSM singlet S. In our framework, S is a meson in a hidden QCD. This QCD is responsible for the dynamical SUSY breaking, forming S, and the soft SUSY breaking mass for S, which is a key to explain the correct EWSB: all the ingredients for successful phenomenology originate from the common dynamics. From the requirement of the successful EWSB, the low-scale SUSY breaking around 100–1000 TeV is predicted. This is favored to avoid the large fine-tuning.

  20. A new scheme for NMSSM in gauge mediation

    Energy Technology Data Exchange (ETDEWEB)

    Asano, Masaki [Physikalisches Institut and Bethe Center for Theoretical Physics, Universität Bonn,Nussallee 12, D-53115 Bonn (Germany); Nakai, Yuichiro [Department of Physics, Harvard University,17 Oxford Street, Cambridge, MA 02138 (United States); Yokozaki, Norimi [Istituto Nazionale di Fisica Nucleare, Sezione di Roma,Piazzale Aldo Moro 2, I-00185 Rome (Italy)

    2016-01-12

    We propose a new framework for the next-to-minimal supersymmetric standard model (NMSSM) in gauge mediation, where in general the correct electroweak symmetry breaking (EWSB) is difficult to be explained. The difficulty is caused by the absence of a soft supersymmetry (SUSY) breaking mass for the NMSSM singlet S. In our framework, S is a meson in a hidden QCD. This QCD is responsible for the dynamical SUSY breaking, forming S, and the soft SUSY breaking mass for S, which is a key to explain the correct EWSB: all the ingredients for successful phenomenology originate from the common dynamics. From the requirement of the successful EWSB, the low-scale SUSY breaking around 100–1000 TeV is predicted. This is favored to avoid the large fine-tuning.

  1. Closed String Tachyons, AdS/CFT, and QCD

    Energy Technology Data Exchange (ETDEWEB)

    Silverstein, Eva M

    2001-07-25

    We find that tachyonic orbifold examples of AdS/CFT have corresponding instabilities at small radius, and can decay to more generic gauge theories. We do this by computing a destabilizing Coleman-Weinberg effective potential for twisted operators of the corresponding quiver gauge theories, generalizing calculations of Tseytlin and Zarembo and interpreting them in terms of the large-N behavior of twisted-sector modes. The dynamically generated potential involves double-trace operators, which affect large-N correlators involving twisted fields but not those involving only untwisted fields, in line with large-N inheritance arguments. We point out a simple reason that no such small radius instability exists in gauge theories arising from freely acting orbifolds, which are tachyon-free at large radius. When an instability is present, twisted gauge theory operators with the quantum numbers of the large-radius tachyons acquire VEVs, leaving a gauge theory with fewer degrees of freedom in the infrared, analogous to but less extreme than ''decays to nothing'' studied in other systems with broken supersymmetry. In some cases one is left with pure glue QCD plus decoupled matter and U(1) factors in the IR, which we thus conjecture is described by the corresponding (possibly strongly coupled) endpoint of tachyon condensation in the M/String-theory dual.

  2. Field strength correlators in QCD: new fits to the lattice data

    International Nuclear Information System (INIS)

    Meggiolaro, E.

    1999-01-01

    We discuss the results obtained by fitting the lattice data of the gauge-invariant field strength correlators in QCD with some particular functions which are commonly used in the literature in some phenomenological approaches to high-energy hadron-hadron scattering. A comparison is done with the results obtained in the original fits to the lattice data. (Copyright (c) 1999 Elsevier Science B.V., Amsterdam. All rights reserved.)

  3. Aspects of confinement in QCD from lattice simulations

    International Nuclear Information System (INIS)

    Spielmann, Daniel

    2011-01-01

    We study confinement in quantum chromodynamics via numerical simulations in the framework of lattice gauge theory. In Landau gauge, the mechanism of confinement is related to the infrared behavior of the ghost and gluon propagators via the Gribov-Zwanziger and Kugo- Ojima scenarios. These scenarios entail a scaling behavior. Functional methods in the continuum allow both for this behavior and for decoupling solutions, while lattice simulations in three and four dimensions yield only the latter. A possible explanation for this mismatch is based on limitations of standard lattice gauge fixing methods. Hence, we investigate a number of alternative gauge fixing algorithms in pure SU(2) gauge theory in two, three and four dimensions. We find that stochastic quantization yields an infrared behavior of the propagators in agreement with the results of standard procedures, even though the Faddeev-Popov operator spectrum indicates some different properties. In the strong-coupling limit, our results challenge the standard picture. In particular, we find in a non-perturbative completion of Landau gauge an enormous effect of the Gribov ambiguity. It entails that no subset of infrared solutions can be excluded yet. Moreover, we study the gluon propagator with free boundary conditions. On large lattices, the results mostly show the standard behavior. We also examine non-periodic gauge transformations. Furthermore, we analyze two topics related to the phase diagram of QCD. First, we explore the sign problem for fermions on the lattice by simulating the three-dimensional Thirring model with a complex Langevin equation. The algorithm succeeds in yielding a 'Silver Blaze' behavior of observables, but it does not reliably describe the onset to a phase with non-zero density. Second, we determine properties of the deconfinement phase transition of pure SU(2) gauge theory in 2+1 dimensions, like the critical temperature, by means of the gluon propagator in Landau gauge. (orig.)

  4. Aspects of confinement in QCD from lattice simulations

    Energy Technology Data Exchange (ETDEWEB)

    Spielmann, Daniel

    2011-01-12

    We study confinement in quantum chromodynamics via numerical simulations in the framework of lattice gauge theory. In Landau gauge, the mechanism of confinement is related to the infrared behavior of the ghost and gluon propagators via the Gribov-Zwanziger and Kugo- Ojima scenarios. These scenarios entail a scaling behavior. Functional methods in the continuum allow both for this behavior and for decoupling solutions, while lattice simulations in three and four dimensions yield only the latter. A possible explanation for this mismatch is based on limitations of standard lattice gauge fixing methods. Hence, we investigate a number of alternative gauge fixing algorithms in pure SU(2) gauge theory in two, three and four dimensions. We find that stochastic quantization yields an infrared behavior of the propagators in agreement with the results of standard procedures, even though the Faddeev-Popov operator spectrum indicates some different properties. In the strong-coupling limit, our results challenge the standard picture. In particular, we find in a non-perturbative completion of Landau gauge an enormous effect of the Gribov ambiguity. It entails that no subset of infrared solutions can be excluded yet. Moreover, we study the gluon propagator with free boundary conditions. On large lattices, the results mostly show the standard behavior. We also examine non-periodic gauge transformations. Furthermore, we analyze two topics related to the phase diagram of QCD. First, we explore the sign problem for fermions on the lattice by simulating the three-dimensional Thirring model with a complex Langevin equation. The algorithm succeeds in yielding a 'Silver Blaze' behavior of observables, but it does not reliably describe the onset to a phase with non-zero density. Second, we determine properties of the deconfinement phase transition of pure SU(2) gauge theory in 2+1 dimensions, like the critical temperature, by means of the gluon propagator in Landau gauge. (orig.)

  5. Report of the 2005 Snowmass Top/QCD Working Group

    Energy Technology Data Exchange (ETDEWEB)

    Juste, A.; /Fermilab; Kiyo, Y.; /Aachen, Tech. Hochsch.; Petriello, F.; /Wisconsin U., Madison /Fermilab; Teubner, T.; /Liverpool U., Dept. Math.; Agashe, K.; Batra, P.; Baur, U.; Berger, C.F.; Cembranos, J.A.R.; Gehrmann-De Ridder, A.; Gehrmann, T.; Glover, E.W.N.; Godfrey, S.; Hoang, A.; Perelstein, M.; Sullivan, Z.; Tait, T.; Zhu, S.; /Johns

    2006-01-17

    This report discusses several topics in both top quark physics and QCD at an International Linear Collider (ILC). Issues such as measurements at the t tbar threshold, including both theoretical and machine requirements, and the determination of electroweak top quark couplings are reviewed. New results concerning the potential of a 500 GeV e+e collider for measuring Wtb couplings and the top quark Yukawa coupling are presented. The status of higher order QCD corrections to jet production cross sections, heavy quark form factors, and longitudinal gauge boson scattering, needed for percent-level studies at the ILC, are reviewed. A new study of the measurement of the hadronic structure of the photon at a gamma gamma collider is presented. The effects on top quark properties from several models of new physics, including composite models, Little Higgs theories, and CPT violation, are studied.

  6. Atomic Quantum Simulations of Abelian and non-Abelian Gauge Theories

    CERN Multimedia

    CERN. Geneva

    2014-01-01

    Using a Fermi-Bose mixture of ultra-cold atoms in an optical lattice, in a collaboration of atomic and particle physicists, we have constructed a quantum simulator for a U(1) gauge theory coupled to fermionic matter. The construction is based on quantum link models which realize continuous gauge symmetry with discrete quantum variables. At low energies, quantum link models with staggered fermions emerge from a Hubbard-type model which can be quantum simulated. This allows investigations of string breaking as well as the real-time evolution after a quench in gauge theories, which are inaccessible to classical simulation methods. Similarly, using ultracold alkaline-earth atoms in optical lattices, we have constructed a quantum simulator for U(N) and SU(N) lattice gauge theories with fermionic matter based on quantum link models. These systems share qualitative features with QCD, including chiral symmetry breaking and restoration at non-zero temperature or baryon density. Unlike classical simulations, a quantum ...

  7. Correlation of the ghost and the quark in the lattice Landau gauge QCD

    International Nuclear Information System (INIS)

    Furui, Sadataka; Nakajima, Hideo

    2007-01-01

    Effects of the quark field on the ghost propagator of the lattice Landau gauge are investigated by using the unquenched SU(3) configurations produced by the MILC collaboration and compared with quenched gauge configurations of SU(2) first copy of the over relaxation gauge fixing, the parallel tempering (PT) gauge fixing and quenched SU(3) 56 4 configurations. We measure the color symmetric and the color antisymmetric ghost propagator and the Binder cumulant of the l 1 norm and the l 2 norm of color antisymmetric ghost propagators and investigate deviation from those of Gaussian distributions. In the first copy samples of quenched SU(2) we observe a large fluctuation in the Binder cumulant at the lowest momentum point. This fluctuation is reduced in the P T gauge fixed samples. The color anti-symmetric ghost propagator of quenched SU(3) configurations depends on the lattice size and is small as compared to the symmetric one in the large lattice of 56 4 . The Binder cumulant of the quenched SU(2) and the N f = 2 + 1 unquenched SU(3) are almost consistent with 3-d and 8-d Gaussian distribution, respectively. A comparison of the SU(3) unquenched configurations and quenched configurations indicates that the dynamical quarks have the effect of making color antisymmetric ghost propagator closer to the Gaussian distribution and the Kugo-Ojima color confinement parameter c closer to 1. (author)

  8. Hadron masses in a gauge theory

    International Nuclear Information System (INIS)

    De Rujula, A.; Georgi, H.; Glashow, S.L.

    1975-01-01

    We explore the implications for hadron spectroscopy of the ''standard'' gauge model of weak, electromagnetic, and strong interactions. The model involves four types of fractionally charged quarks, each in three colors, coupling to massless gauge gluons. The quarks are confined within colorless hadrons by a long-range spin-independent force realizing infrared slavery. We use the asymptotic freedom of the model to argue that for the calculation of hadron masses, the short-range quark-quark interaction may be taken to be Coulomb-like. We rederive many successful quark-model mass relations for the low-lying hadrons. Because a specific interaction and symmetry-breaking mechanism are forced on us by the underlying renormalizable gauge field theory, we also obtain new mass relations. They are well satisfied. We develop a qualitative understanding of many features of the hadron mass spectrum, such as the origin and sign of the Σ-Λ mass splitting. Interpreting the newly discovered narrow boson resonances as states of charmonium, we use the model to predict the masses of charmed mesons and baryons

  9. Lattice simulations of QCD-like theories at finite baryon density

    Energy Technology Data Exchange (ETDEWEB)

    Scior, Philipp Friedrich

    2016-07-13

    The exploration of the phase diagram of quantum chromodynamics (QCD) is of great importance to describe e.g. the properties of neutron stars or heavy-ion collisions. Due to the sign problem of lattice QCD at finite chemical potential we need effective theories to study QCD at finite density. Here, we use a three-dimensional Polyakov-loop theory to study the phase diagrams of QCD-like theories. In particular, we investigate the heavy quark limit of the QCD-like theories where the effective theory can be derived from the full theory by a combined strong coupling and hopping expansion. This expansion can be systematically improved order by order. Since there is no sign problem for the QCD-like theories we consider, we can compare our results to data from lattice calculations of the full theories to make qualitative and quantitative statements of the effective theory's validity. We start by deriving the effective theory up to next-to-next-to leading-order, in particular for two-color and G{sub 2}-QCD where replace the three colors in QCD with only two colors or respectively replace the gauge group SU(3) of QCD with G{sub 2}. We will then apply the effective theory at finite temperature mainly to test the theory and the implementation but also to make some predictions for the deconfinement phase transition in G{sub 2} Yang-Mills theory. Finally, we turn our attention to the cold and dense regime of the phase diagram where we observe a sharp increase of the baryon density with the quark chemical potential μ, when μ reaches half the diquark mass. At vanishing temperature this is expected to happen in a quantum phase transition with Bose-Einstein-condensation of diquarks. In contrast to the liquid-gas transition in QCD, the phase transition to the Bose-Einstein condensate is continuous. We find evidence that the effective theories for heavy quarks are able to describe the qualitative difference between first and second order phase transitions. For even higher μ we

  10. Lattice simulations of QCD-like theories at finite baryon density

    International Nuclear Information System (INIS)

    Scior, Philipp Friedrich

    2016-01-01

    The exploration of the phase diagram of quantum chromodynamics (QCD) is of great importance to describe e.g. the properties of neutron stars or heavy-ion collisions. Due to the sign problem of lattice QCD at finite chemical potential we need effective theories to study QCD at finite density. Here, we use a three-dimensional Polyakov-loop theory to study the phase diagrams of QCD-like theories. In particular, we investigate the heavy quark limit of the QCD-like theories where the effective theory can be derived from the full theory by a combined strong coupling and hopping expansion. This expansion can be systematically improved order by order. Since there is no sign problem for the QCD-like theories we consider, we can compare our results to data from lattice calculations of the full theories to make qualitative and quantitative statements of the effective theory's validity. We start by deriving the effective theory up to next-to-next-to leading-order, in particular for two-color and G_2-QCD where replace the three colors in QCD with only two colors or respectively replace the gauge group SU(3) of QCD with G_2. We will then apply the effective theory at finite temperature mainly to test the theory and the implementation but also to make some predictions for the deconfinement phase transition in G_2 Yang-Mills theory. Finally, we turn our attention to the cold and dense regime of the phase diagram where we observe a sharp increase of the baryon density with the quark chemical potential μ, when μ reaches half the diquark mass. At vanishing temperature this is expected to happen in a quantum phase transition with Bose-Einstein-condensation of diquarks. In contrast to the liquid-gas transition in QCD, the phase transition to the Bose-Einstein condensate is continuous. We find evidence that the effective theories for heavy quarks are able to describe the qualitative difference between first and second order phase transitions. For even higher μ we find the rise of the

  11. D3-brane shells to black branes on the Coulomb branch

    International Nuclear Information System (INIS)

    Giddings, Steven B.; Ross, Simon F.

    2000-01-01

    We use the AdS-CFT duality to study the special point on the Coulomb branch of N=4 SU(N) gauge theory which corresponds to a spherically symmetric shell of D3-branes. This point is of interest both because the spacetime region inside the shell is flat, and because this configuration gives a very simple example of the transition between D-branes in the perturbative string regime and the nonperturbative regime of black holes. We discuss how this geometry is described in the dual gauge theory, through its effect on the two-point functions and Wilson loops. In the calculation of the two-point function, we stress the importance of absorption by the branes. (c) 1999 The American Physical Society

  12. Renormalization of Supersymmetric QCD on the Lattice

    Science.gov (United States)

    Costa, Marios; Panagopoulos, Haralambos

    2018-03-01

    We perform a pilot study of the perturbative renormalization of a Supersymmetric gauge theory with matter fields on the lattice. As a specific example, we consider Supersymmetric N=1 QCD (SQCD). We study the self-energies of all particles which appear in this theory, as well as the renormalization of the coupling constant. To this end we compute, perturbatively to one-loop, the relevant two-point and three-point Green's functions using both dimensional and lattice regularizations. Our lattice formulation involves theWilson discretization for the gluino and quark fields; for gluons we employ the Wilson gauge action; for scalar fields (squarks) we use naive discretization. The gauge group that we consider is SU(Nc), while the number of colors, Nc, the number of flavors, Nf, and the gauge parameter, α, are left unspecified. We obtain analytic expressions for the renormalization factors of the coupling constant (Zg) and of the quark (ZΨ), gluon (Zu), gluino (Zλ), squark (ZA±), and ghost (Zc) fields on the lattice. We also compute the critical values of the gluino, quark and squark masses. Finally, we address the mixing which occurs among squark degrees of freedom beyond tree level: we calculate the corresponding mixing matrix which is necessary in order to disentangle the components of the squark field via an additional finite renormalization.

  13. QCD-instantons at LHC. Theoretical aspects; QCD-Instantonen am LHC. Theoretische Aspekte

    Energy Technology Data Exchange (ETDEWEB)

    Petermann, M.

    2007-06-15

    Instantons are nonperturbative, topologically nontrivial field configurations, which occur in every nonabelian gauge theory. They can be understood as tunneling processes between topologically distinct vacua. Although being a basic theoretical aspect of the Standard Model, a direct experimental verification of instanton processes is still lacking. In this thesis the general discovery potential for QCD-instantons at the LHC is studied in detail by means of instanton perturbation theory. In this context the close correspondence between the leading instanton induced processes at HERA and at LHC becomes important. Essential aspects and differences to deep inelastic scattering can already be revealed by studying the simplest process. Based on these results inclusive cross sections are calculated including the emission of final state gluons. Compared to deep inelastic scattering, a large enhancement of the cross section is found. (orig.)

  14. A gauge-invariant reorganization of thermal gauge theory

    Energy Technology Data Exchange (ETDEWEB)

    Su, Nan

    2010-07-01

    This dissertation is devoted to the study of thermodynamics for quantum gauge theories. The poor convergence of quantum field theory at finite temperature has been the main obstacle in the practical applications of thermal QCD for decades. In this dissertation I apply hard-thermal-loop perturbation theory, which is a gauge-invariant reorganization of the conventional perturbative expansion for quantum gauge theories to the thermodynamics of QED and Yang-Mills theory to three-loop order. For the Abelian case, I present a calculation of the free energy of a hot gas of electrons and photons by expanding in a power series in m{sub D}/T, m{sub f}/T and e{sup 2}, where m{sub D} and m{sub f} are the photon and electron thermal masses, respectively, and e is the coupling constant. I demonstrate that the hard-thermal-loop perturbation reorganization improves the convergence of the successive approximations to the QED free energy at large coupling, e {proportional_to} 2. For the non-Abelian case, I present a calculation of the free energy of a hot gas of gluons by expanding in a power series in m{sub D}/T and g{sup 2}, where m{sub D} is the gluon thermal mass and g is the coupling constant. I show that at three-loop order hard-thermal-loop perturbation theory is compatible with lattice results for the pressure, energy density, and entropy down to temperatures T {proportional_to} 2 - 3 T{sub c}. The results suggest that HTLpt provides a systematic framework that can be used to calculate static and dynamic quantities for temperatures relevant at LHC. (orig.)

  15. Universal monopole scaling near transitions from the Coulomb phase.

    Science.gov (United States)

    Powell, Stephen

    2012-08-10

    Certain frustrated systems, including spin ice and dimer models, exhibit a Coulomb phase at low temperatures, with power-law correlations and fractionalized monopole excitations. Transitions out of this phase, at which the effective gauge theory becomes confining, provide examples of unconventional criticality. This Letter studies the behavior at nonzero monopole density near such transitions, using scaling theory to arrive at universal expressions for the crossover phenomena. For a particular transition in spin ice, quantitative predictions are made by mapping to the XY model and confirmed using Monte Carlo simulations.

  16. Duality in a Supersymmetric Gauge Theory From a Perturbative Viewpoint

    DEFF Research Database (Denmark)

    Ryttov, Thomas A.; Shrock, Robert

    2018-01-01

    points of the renormalization group emerge in scheme-independent series expansions in the electric and magnetic theories. We further demonstrate that truncations of these series expansions to modest order yield very accurate approximations to these quantities and suggest possible implications......We study duality in N ¼ 1 supersymmetric QCD in the non-Abelian Coulomb phase, order-by-order in scheme-independent series expansions. Using exact results, we show how the dimensions of various fundamental and composite chiral superfields, and the quantities a, c, a=c, and b at superconformal fixed...

  17. Asymmetric dark matter and the hadronic spectra of hidden QCD

    Science.gov (United States)

    Lonsdale, Stephen J.; Schroor, Martine; Volkas, Raymond R.

    2017-09-01

    The idea that dark matter may be a composite state of a hidden non-Abelian gauge sector has received great attention in recent years. Frameworks such as asymmetric dark matter motivate the idea that dark matter may have similar mass to the proton, while mirror matter and G ×G grand unified theories provide rationales for additional gauge sectors which may have minimal interactions with standard model particles. In this work we explore the hadronic spectra that these dark QCD models can allow. The effects of the number of light colored particles and the value of the confinement scale on the lightest stable state, the dark matter candidate, are examined in the hyperspherical constituent quark model for baryonic and mesonic states.

  18. Hadronic final states in high -pT QCD at CDF

    Energy Technology Data Exchange (ETDEWEB)

    Matera, Keith [University of Illinois, Urbana-Champaign

    2013-11-18

    The heavy quark content of gauge boson events is of great interest to studies of QCD. These events probe the gluon and heavy-quark parton distribution functions of the proton, and also provide a measurement of the rate of final state gluon splitting to heavy flavor. In addition, gauge boson plus heavy quark events are representative of backgrounds to Higgs, single top, and supersymmetric particle searches. Recent work with the CDF II detector at the Fermilab Tevatron has measured the cross-section of several gauge boson plus heavy flavor production processes, including the first Tevatron observation of specific charm process p{p bar} → W +c. Results are found to be in agreement with NLO predictions that include an enhanced rate of g → {cc bar}/bb splitting. Lastly, a new analysis promises to probe a lower pT (c) region than has been previously explored, by fully reconstructing D* → D0(Kπ)π decays in the full CDF dataset (9.7 fb-1).

  19. Renormalization of composite operators in Yang-Mills theories using a general covariant gauge

    International Nuclear Information System (INIS)

    Collins, J.C.; Scalise, R.J.

    1994-01-01

    Essential to QCD applications of the operator product expansion, etc., is a knowledge of those operators that mix with gauge-invariant operators. A standard theorem asserts that the renormalization matrix is triangular: Gauge-invariant operators have ''alien'' gauge-variant operators among their counterterms, but, with a suitably chosen basis, the necessary alien operators have only themselves as counterterms. Moreover, the alien operators are supposed to vanish in physical matrix elements. A recent calculation by Hamberg and van Neerven apparently contradicts these results. By explicit calculations with the energy-momentum tensor, we show that the problems arise because of subtle infrared singularities that appear when gluonic matrix elements are taken on shell at zero momentum transfer

  20. Holographic QCD beyond the leading order

    International Nuclear Information System (INIS)

    Kim, Youngman; Ko, P.; Wu, Xiao-Hong

    2008-01-01

    We consider a holographic QCD model for light mesons beyond the leading order in the context of 5-dim gauged linear sigma model on the interval in the AdS 5 space. We include two dimension-6 operators in addition to the canonical bulk kinetic terms, and study chiral dynamics of π, ρ, a 1 and some of their KK modes. As novel features of dim-6 operators, we get non-vanishing Br(a 1 → πγ), the electromagnetic form factor and the charge radius of a charged pion, which improve the leading order results significantly and agree well with the experimental results.

  1. Non-perturbative O(a) improvement of lattice QCD

    CERN Document Server

    Lüscher, Martin; Sommer, Rainer; Weisz, P; Wolff, U; Luescher, Martin; Sint, Stefan; Sommer, Rainer; Weisz, Peter; Wolff, Ulli

    1997-01-01

    The coefficients multiplying the counterterms required for O($a$) improvement of the action and the isovector axial current in lattice QCD are computed non-perturbatively, in the quenched approximation and for bare gauge couplings $g_0$ in the range $0 \\leq g_0 \\leq 1$. A finite-size method based on the Schrödinger functional is employed, which enables us to perform all calculations at zero or nearly zero quark mass. As a by-product the critical hopping parameter $\\kappa_c$ is obtained at all couplings considered.

  2. The arithmetic of elliptic fibrations in gauge theories on a circle

    Energy Technology Data Exchange (ETDEWEB)

    Grimm, Thomas W. [Max-Planck-Institut für Physik,Föhringer Ring 6, 80805 Munich (Germany); Institute for Theoretical Physics,Utrecht University, Leuvenlaan 4, 3584 CE Utrecht (Netherlands); Center for Extreme Matter and Emergent Phenomena,Utrecht University, Leuvenlaan 4, 3584 CE Utrecht (Netherlands); Kapfer, Andreas [Max-Planck-Institut für Physik,Föhringer Ring 6, 80805 Munich (Germany); Klevers, Denis [Theory Group, Physics Department, CERN,CH-1211, Geneva 23 (Switzerland)

    2016-06-20

    The geometry of elliptic fibrations translates to the physics of gauge theories in F-theory. We systematically develop the dictionary between arithmetic structures on elliptic curves as well as desingularized elliptic fibrations and symmetries of gauge theories on a circle. We show that the Mordell-Weil group law matches integral large gauge transformations around the circle in Abelian gauge theories and explain the significance of Mordell-Weil torsion in this context. We also use Higgs transitions and circle large gauge transformations to introduce a group law for genus-one fibrations with multi-sections. Finally, we introduce a novel arithmetic structure on elliptic fibrations with non-Abelian gauge groups in F-theory. It is defined on the set of exceptional divisors resolving the singularities and divisor classes of sections of the fibration. This group structure can be matched with certain integral non-Abelian large gauge transformations around the circle when studying the theory on the lower-dimensional Coulomb branch. Its existence is required by consistency with Higgs transitions from the non-Abelian theory to its Abelian phases in which it becomes the Mordell-Weil group. This hints towards the existence of a new underlying geometric symmetry.

  3. The arithmetic of elliptic fibrations in gauge theories on a circle

    Science.gov (United States)

    Grimm, Thomas W.; Kapfer, Andreas; Klevers, Denis

    2016-06-01

    The geometry of elliptic fibrations translates to the physics of gauge theories in F-theory. We systematically develop the dictionary between arithmetic structures on elliptic curves as well as desingularized elliptic fibrations and symmetries of gauge theories on a circle. We show that the Mordell-Weil group law matches integral large gauge transformations around the circle in Abelian gauge theories and explain the significance of Mordell-Weil torsion in this context. We also use Higgs transitions and circle large gauge transformations to introduce a group law for genus-one fibrations with multi-sections. Finally, we introduce a novel arithmetic structure on elliptic fibrations with non-Abelian gauge groups in F-theory. It is defined on the set of exceptional divisors resolving the singularities and divisor classes of sections of the fibration. This group structure can be matched with certain integral non-Abelian large gauge transformations around the circle when studying the theory on the lower-dimensional Coulomb branch. Its existence is required by consistency with Higgs transitions from the non-Abelian theory to its Abelian phases in which it becomes the Mordell-Weil group. This hints towards the existence of a new underlying geometric symmetry.

  4. The arithmetic of elliptic fibrations in gauge theories on a circle

    International Nuclear Information System (INIS)

    Grimm, Thomas W.; Kapfer, Andreas; Klevers, Denis

    2016-01-01

    The geometry of elliptic fibrations translates to the physics of gauge theories in F-theory. We systematically develop the dictionary between arithmetic structures on elliptic curves as well as desingularized elliptic fibrations and symmetries of gauge theories on a circle. We show that the Mordell-Weil group law matches integral large gauge transformations around the circle in Abelian gauge theories and explain the significance of Mordell-Weil torsion in this context. We also use Higgs transitions and circle large gauge transformations to introduce a group law for genus-one fibrations with multi-sections. Finally, we introduce a novel arithmetic structure on elliptic fibrations with non-Abelian gauge groups in F-theory. It is defined on the set of exceptional divisors resolving the singularities and divisor classes of sections of the fibration. This group structure can be matched with certain integral non-Abelian large gauge transformations around the circle when studying the theory on the lower-dimensional Coulomb branch. Its existence is required by consistency with Higgs transitions from the non-Abelian theory to its Abelian phases in which it becomes the Mordell-Weil group. This hints towards the existence of a new underlying geometric symmetry.

  5. Parton densities in quantum chromodynamics. Gauge invariance, path-dependence, and Wilson lines

    International Nuclear Information System (INIS)

    Cherednikov, Igor O.

    2017-01-01

    The purpose of this book is to give a systematic pedagogical exposition of the quantitative analysis of Wilson lines and gauge-invariant correlation functions in quantum chromodynamics. Using techniques from the previous volume (Wilson Lines in Quantum Field Theory, 2014), an ab initio methodology is developed and practical tools for its implementation are presented. Emphasis is put on the implications of gauge invariance and path-dependence properties of transverse-momentum dependent parton density functions. The latter are associated with the QCD factorization approach to semi-inclusive hadronic processes, studied at currently operating and planned experimental facilities.

  6. Parton densities in quantum chromodynamics. Gauge invariance, path-dependence, and Wilson lines

    Energy Technology Data Exchange (ETDEWEB)

    Cherednikov, Igor O. [Antwerpen Univ. (Belgium). Dept. Fysica; Veken, Frederik F. van der [CERN, Geneva (Switzerland)

    2017-05-01

    The purpose of this book is to give a systematic pedagogical exposition of the quantitative analysis of Wilson lines and gauge-invariant correlation functions in quantum chromodynamics. Using techniques from the previous volume (Wilson Lines in Quantum Field Theory, 2014), an ab initio methodology is developed and practical tools for its implementation are presented. Emphasis is put on the implications of gauge invariance and path-dependence properties of transverse-momentum dependent parton density functions. The latter are associated with the QCD factorization approach to semi-inclusive hadronic processes, studied at currently operating and planned experimental facilities.

  7. Infrared exponents and the strong-coupling limit in lattice Landau gauge

    International Nuclear Information System (INIS)

    Sternbeck, Andre; Smekal, Lorenz von

    2010-01-01

    We study the gluon and ghost propagators of lattice Landau gauge in the strong-coupling limit β=0 in pure SU(2) lattice gauge theory to find evidence of the conformal infrared behavior of these propagators as predicted by a variety of functional continuum methods for asymptotically small momenta q 2 QCD 2 . In the strong-coupling limit, this same behavior is obtained for the larger values of a 2 q 2 (in units of the lattice spacing a), where it is otherwise swamped by the gauge-field dynamics. Deviations for a 2 q 2 <1 are well parameterized by a transverse gluon mass ∝1/a. Perhaps unexpectedly, these deviations are thus no finite-volume effect but persist in the infinite-volume limit. They furthermore depend on the definition of gauge fields on the lattice, while the asymptotic conformal behavior does not. We also comment on a misinterpretation of our results by Cucchieri and Mendes (Phys. Rev. D 81:016005, 2010). (orig.)

  8. Spin-2 NΩ dibaryon from lattice QCD

    International Nuclear Information System (INIS)

    Etminan, Faisal; Nemura, Hidekatsu; Aoki, Sinya; Doi, Takumi; Hatsuda, Tetsuo; Ikeda, Yoichi; Inoue, Takashi; Ishii, Noriyoshi; Murano, Keiko; Sasaki, Kenji

    2014-01-01

    We investigate properties of the N(nucleon)–Ω(Omega) interaction in lattice QCD to seek for possible dibaryon states in the strangeness −3 channel. We calculate the NΩ potential through the equal-time Nambu–Bethe–Salpeter wave function in 2+1 flavor lattice QCD with the renormalization group improved Iwasaki gauge action and the nonperturbatively O(a) improved Wilson quark action at the lattice spacing a≃0.12 fm on a (1.9 fm) 3 × 3.8 fm lattice. The ud and s quark masses in our study correspond to m π =875(1) MeV and m K =916(1) MeV. At these parameter values, the central potential in the S-wave with the spin 2 shows attractions at all distances. By solving the Schrödinger equation with this potential, we find one bound state whose binding energy is 18.9(5.0)( +12.1 −1.8 ) MeV, where the first error is the statistical one, while the second represents the systematic error

  9. Spin-2 NΩ dibaryon from lattice QCD

    Energy Technology Data Exchange (ETDEWEB)

    Etminan, Faisal [Center for Computational Sciences, University of Tsukuba, Ibaraki 305-8571 (Japan); Department of Physics, Faculty of Sciences, University of Birjand, Birjand 97175-615 (Iran, Islamic Republic of); Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502 (Japan); Nemura, Hidekatsu [Center for Computational Sciences, University of Tsukuba, Ibaraki 305-8571 (Japan); Aoki, Sinya [Center for Computational Sciences, University of Tsukuba, Ibaraki 305-8571 (Japan); Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502 (Japan); Doi, Takumi [Theoretical Research Division, Nishina Center, RIKEN, Saitama 351-0198 (Japan); Hatsuda, Tetsuo [Theoretical Research Division, Nishina Center, RIKEN, Saitama 351-0198 (Japan); Kavli IPMU (WPI), The University of Tokyo, Chiba 277-8583 (Japan); Ikeda, Yoichi [Theoretical Research Division, Nishina Center, RIKEN, Saitama 351-0198 (Japan); Inoue, Takashi [Nihon University, College of Bioresource Sciences, Kanagawa 252-0880 (Japan); Ishii, Noriyoshi [Center for Computational Sciences, University of Tsukuba, Ibaraki 305-8571 (Japan); Murano, Keiko [Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502 (Japan); Sasaki, Kenji [Center for Computational Sciences, University of Tsukuba, Ibaraki 305-8571 (Japan)

    2014-08-15

    We investigate properties of the N(nucleon)–Ω(Omega) interaction in lattice QCD to seek for possible dibaryon states in the strangeness −3 channel. We calculate the NΩ potential through the equal-time Nambu–Bethe–Salpeter wave function in 2+1 flavor lattice QCD with the renormalization group improved Iwasaki gauge action and the nonperturbatively O(a) improved Wilson quark action at the lattice spacing a≃0.12 fm on a (1.9 fm){sup 3}× 3.8 fm lattice. The ud and s quark masses in our study correspond to m{sub π}=875(1) MeV and m{sub K}=916(1) MeV. At these parameter values, the central potential in the S-wave with the spin 2 shows attractions at all distances. By solving the Schrödinger equation with this potential, we find one bound state whose binding energy is 18.9(5.0)({sup +12.1}{sub −1.8}) MeV, where the first error is the statistical one, while the second represents the systematic error.

  10. NLO QCD effective field theory analysis of W+W- production at the LHC including fermionic operators

    Science.gov (United States)

    Baglio, Julien; Dawson, Sally; Lewis, Ian M.

    2017-10-01

    We study the impact of anomalous gauge boson and fermion couplings on the production of W+W- pairs at the LHC. Helicity amplitudes are presented separately to demonstrate the sources of new physics contributions and the impact of QCD and electroweak corrections. The QCD corrections have important effects on the fits to anomalous couplings, in particular when one W boson is longitudinally polarized and the other is transversely polarized. In effective field theory language, we demonstrate that the dimension-6 approximation to constraining new physics effects in W+W- pair production fails at pT˜500 - 1000 GeV .

  11. Infrared finite ghost propagator in the Feynman gauge

    International Nuclear Information System (INIS)

    Aguilar, A. C.; Papavassiliou, J.

    2008-01-01

    We demonstrate how to obtain from the Schwinger-Dyson equations of QCD an infrared finite ghost propagator in the Feynman gauge. The key ingredient in this construction is the longitudinal form factor of the nonperturbative gluon-ghost vertex, which, contrary to what happens in the Landau gauge, contributes nontrivially to the gap equation of the ghost. The detailed study of the corresponding vertex equation reveals that in the presence of a dynamical infrared cutoff this form factor remains finite in the limit of vanishing ghost momentum. This, in turn, allows the ghost self-energy to reach a finite value in the infrared, without having to assume any additional properties for the gluon-ghost vertex, such as the presence of massless poles. The implications of this result and possible future directions are briefly outlined

  12. Unified models of the QCD axion and supersymmetry breaking

    Directory of Open Access Journals (Sweden)

    Keisuke Harigaya

    2017-08-01

    Full Text Available Similarities between the gauge meditation of supersymmetry breaking and the QCD axion model suggest that they originate from the same dynamics. We present a class of models where supersymmetry and the Peccei–Quinn symmetry are simultaneously broken. The messengers that mediate the effects of these symmetry breakings to the Standard Model are identical. Since the axion resides in the supersymmetry breaking sector, the saxion and the axino are heavy. We show constraints on the axion decay constant and the gravitino mass.

  13. A new scheme for the running coupling constant in gauge theories using Wilson loops

    Energy Technology Data Exchange (ETDEWEB)

    Kurachi, Masafumi [Los Alamos National Laboratory; Bilgici, Erek [AUSTRIA; Flachi, Antonion [KYOTO UNIV; Itou, Etsuko [KOGAKUIN UNIV; David Lin, C J [NATIONAL CHIAO-TUNG UNIV; Matsufuru, Hideo [KEK; Ohki, Hiroshi [KYOTO UNIV; Onogi, Tetsuya [KYOTO UNIV; Yamazaki, Takeshi [UNIV OF TSUKUBA

    2009-01-01

    We propose a new renormalization scheme of the running coupling constant in general gauge theories defined by using the Wilson loops. The renormalized coupling constant is obtained from the Cretz ratio in lattice simulations and the corresponding perturbative coefficient at the leading order. The latter calculation is performed by adopting the zeta-function resummation techniques. We make a benchmark test of our scheme in quenched QCD with the plaquette gauge action. The running of the coupling constant is determined by applying the step scaling procedure. Using several methods to improve the statistical accuracy, we show that the running coupling constant can be determined in a wide range of energy scales with relatively small number of gauge configurations.

  14. The universality of the confining potential and the running of the quasi-Coulombic potential constant in the independent-quark model

    International Nuclear Information System (INIS)

    Khruschev, V.V.; Savrin, V.I.; Semenov, S.V.

    1999-01-01

    Parameters of the QCD-motivated static potential and the quark masses are calculated on the basis of the 1 -- meson mass spectra in the framework of the relativistic independent-quark model based on the Dirac equation. The value of the confining potential parameter is found to be (0.20 ± 0.01) GeV 2 for interactions between quarks and antiquarks independently on their flavors. The flavor independence of the confining potential is justified on the 5 x 10 -2 accuracy level both for the heavy quarks and for the light ones. The values of parameter α s , which is a strength of the quasi-Coulombic potential are consistent with the QCD-motivated decrease of α s at small interaction range [ru

  15. Lattice gauge fixing as quenching and the violation of spectral positivity

    International Nuclear Information System (INIS)

    Aubin, C.; Ogilvie, Michael C.

    2004-01-01

    Lattice Landau gauge and other related lattice gauge-fixing schemes are known to violate spectral positivity. The most direct sign of the violation is the rise of the effective mass as a function of distance. The origin of this phenomenon lies in the quenched character of the auxiliary field g used to implement lattice gauge-fixing, and is similar to quenched QCD in this respect. This is best studied using the Parrinello Jona-Lasinio Zwanziger formalism, leading to a class of covariant gauges similar to the one-parameter class of covariant gauges commonly used in continuum gauge theories. Soluble models are used to illustrate the origin of the violation of spectral positivity. The phase diagram of the lattice theory, as a function of the gauge coupling β and the gauge-fixing parameter α, is similar to that of the unquenched theory, a Higgs model of a type first studied by Fradkin and Shenker. The gluon propagator is interpreted as yielding bound states in the confined phase, and a mixture of fundamental particles in the Higgs phase, but lattice simulation shows the two phases are connected. Gauge-field propagators from the simulation of an SU(2) lattice gauge theory on a 20 4 lattice are well described by a quenched mass-mixing model. The mass of the lightest state, which we interpret as the gluon mass, appears to be independent of α for sufficiently large α

  16. Coulomb excitation

    International Nuclear Information System (INIS)

    McGowan, F.K.; Stelson, P.H.

    1974-01-01

    The theory of Coulomb excitation and a brief review of pertinent treatments of the Coulomb excitation process that are useful for the analysis of experiments are given. Examples demonstrating the scope of nuclear structure information obtainable from gamma spectroscopy are presented. Direct Elambda excitation of 232 Th is discussed in terms of the one phonon octupole vibrational spectrum. B(MI) reduced transition probabilities resulting from Coulomb excitation of odd-A deformed nuclei with heavy ions are presented as a test of the rotational model. The use of gamma ray coincidence and particle-gamma coincidence as tools for investigating Coulomb excitation is discussed. (U.S.)

  17. New Perspectives for Hadron Phenomenology:The Effects of Final-State Interactions and Near-Conformal Effective QCD Couplings

    Energy Technology Data Exchange (ETDEWEB)

    Brodsky, S

    2003-10-24

    The effective QCD charge extracted from {tau} decay is remarkably constant at small momenta, implying the near-conformal behavior of hadronic interactions at small momentum transfer. The correspondence of large-N{sub c} supergravity theory in higher-dimensional anti-de Sitter spaces with gauge theory in physical space-time also has interesting implications for hadron phenomenology in the conformal limit, such as constituent counting rules for hard exclusive processes. The utility of light-front quantization and lightfront Fock wavefunctions for analyzing such phenomena and representing the dynamics of QCD bound states is reviewed. I also discuss the novel effects of initial- and final-state interactions in hard QCD inclusive processes, including Bjorken-scaling single-spin asymmetries and the leading-twist diffractive and shadowing contributions to deep inelastic lepton-proton scattering.

  18. Computing K and D meson masses with N-f=2+1+1 twisted mass lattice QCD

    NARCIS (Netherlands)

    Baron, Remi; Boucaud, Philippe; Carbonell, Jaume; Drach, Vincent; Farchioni, Federico; Herdoiza, Gregorio; Jansen, Karl; Michael, Chris; Montvay, Istvan; Pallante, Elisabetta; Pene, Olivier; Reker, Siebren; Urbach, Carsten; Wagner, Marc; Wenger, Urs

    We discuss the computation of the mass of the K and D mesons within the framework of N-f = 2 + 1 + 1 twisted mass lattice QCD from a technical point of view. These quantities are essential, already at the level of generating gauge configurations, being obvious candidates to tune the strange and

  19. A scaling study of the step scaling function of quenched QCD with improved gauge actions

    International Nuclear Information System (INIS)

    Takeda, S.; Aoki, S.; Fukugita, M.; Ishikawa, K-I.; Ishizuka, N.; Iwasaki, Y.; Kanaya, K.; Kaneko, T.; Kuramashi, Y.; Okawa, M.; Taniguchi, Y.; Ukawa, A.; Yoshie, T.

    2005-01-01

    We study the scaling behavior of the step scaling function for SU(3) gauge theory, employing the Iwasaki gauge action and the Luescher-Weisz gauge action. In particular, we test the choice of boundary counter terms and apply a perturbative procedure for removal of lattice artifacts for the simulation results in the extrapolation procedure. We confirm the universality of the step scaling functions at both weak and strong coupling regions. We also measure the low energy scale ratio with the Iwasaki action, and confirm its universality

  20. Thermalization and confinement in strongly coupled gauge theories

    Directory of Open Access Journals (Sweden)

    Ishii Takaaki

    2016-01-01

    Full Text Available Quantum field theories of strongly interacting matter sometimes have a useful holographic description in terms of the variables of a gravitational theory in higher dimensions. This duality maps time dependent physics in the gauge theory to time dependent solutions of the Einstein equations in the gravity theory. In order to better understand the process by which “real world” theories such as QCD behave out of thermodynamic equilibrium, we study time dependent perturbations to states in a model of a confining, strongly coupled gauge theory via holography. Operationally, this involves solving a set of non-linear Einstein equations supplemented with specific time dependent boundary conditions. The resulting solutions allow one to comment on the timescale by which the perturbed states thermalize, as well as to quantify the properties of the final state as a function of the perturbation parameters. We comment on the influence of the dual gauge theory’s confinement scale on these results, as well as the appearance of a previously anticipated universal scaling regime in the “abrupt quench” limit.

  1. AdS/QCD, Light-Front Holography, and Sublimated Gluons

    Energy Technology Data Exchange (ETDEWEB)

    Brodsky, Stanley J.; /SLAC; de Teramond, Guy F.; /Costa Rica U.

    2012-02-16

    The gauge/gravity duality leads to a simple analytical and phenomenologically compelling nonperturbative approximation to the full light-front QCD Hamiltonian - 'Light-Front Holography', which provides a Lorentz-invariant first-approximation to QCD, and successfully describes the spectroscopy of light-quark meson and baryons, their elastic and transition form factors, and other hadronic properties. The bound-state Schroedinger and Dirac equations of the soft-wall AdS/QCD model predict linear Regge trajectories which have the same slope in orbital angular momentum L and radial quantum number n for both mesons and baryons. Light-front holography connects the fifth-dimensional coordinate of AdS space z to an invariant impact separation variable {zeta} in 3+1 space at fixed light-front time. A key feature is the determination of the frame-independent light-front wavefunctions of hadrons - the relativistic analogs of the Schroedinger wavefunctions of atomic physics which allow one to compute form factors, transversity distributions, spin properties of the valence quarks, jet hadronization, and other hadronic observables. One thus obtains a one-parameter color-confining model for hadron physics at the amplitude level. AdS/QCD also predicts the form of the non-perturbative effective coupling {alpha}{sub s}{sup AdS} (Q) and its {beta}-function with an infrared fixed point which agrees with the effective coupling a{sub g1} (Q{sup 2}) extracted from measurements of the Bjorken sum rule below Q{sup 2} < 1 GeV{sup 2}. This is consistent with a flux-tube interpretation of QCD where soft gluons with virtualities Q{sup 2} < 1 GeV{sup 2} are sublimated into a color-confining potential for quarks. We discuss a number of phenomenological hadronic properties which support this picture.

  2. Charmed meson decay constants in three-flavor lattice QCD

    Energy Technology Data Exchange (ETDEWEB)

    Aubin, C.; Bernard, C.; DeTar, C.; Di Pierro, M.; Freeland, Elizabeth D.; Gottlieb, Steven; Heller, U.M.; Hetrick, J.E.; El-Khadra, Aida X.; Kronfeld, Andreas S.; Levkova, L.; Mackenzie, P.B.; Menscher, D.; Maresca, F.; Nobes, M.; Okamoto, M.; Renner, D.B.; Simone, J.; Sugar, R.; Toussaint, D.; Trottier, H.D.; /Art Inst. of Chicago /Columbia

    2005-06-01

    The authors present the first lattice QCD calculation with realistic sea quark content of the D{sup +}-meson decay constant f{sub D+}. They use the MILC Collaboration's publicly available ensembles of lattice gauge fields, which have a quark sea with two flavors (up and down) much lighter than a third (strange). They obtain f{sub D+} = 201 {+-} 3 {+-} 17 MeV, where the errors are statistical and a combination of systematic errors. They also obtain f{sub D{sub s}} = 249 {+-} 3 {+-} 16 MeV for the D{sub s} meson.

  3. Higher order effects of pseudoparticles in QCD

    International Nuclear Information System (INIS)

    Hietarinta, J.; Palmer, W.F.

    1977-01-01

    Gauge invariant Green's functions of quark-antiquark bilinear densities in massless, two-color QCD are studied. Nonzero-energy fermion modes, pseudoparticle solutions with topological charge absolute value ν > 1, and n-point functions with n > 2. Some general properties of the O(Dirac constant) approximation are developed, enabling one to isolate and define the terms which contribute to a general n-point function. The higher effects it is found preserve the symmetry breakdown found earlier in the 2-point function (U(2) x U(2) → SU(2) x SU(2) x U(1)). It is shown that a previous 2-point function analysis is exact to order Dirac constant

  4. Exploring the structure of the quenched QCD vacuum with overlap fermions

    International Nuclear Information System (INIS)

    Ilgenfritz, E.M.; Koller, K.; Koma, Y.; Schierholz, G.; Deutsches Elektronen-Synchrotron; Streuer, T.; Weinberg, V.; Freie Univ. Berlin

    2007-05-01

    Overlap fermions have an exact chiral symmetry on the lattice and are thus an appropriate tool for investigating the chiral and topological structure of the QCD vacuum. We study various chiral and topological aspects of quenched gauge field configurations. This includes the localization and chiral properties of the eigenmodes, the local structure of the ultraviolet filtered field strength tensor, as well as the structure of topological charge fluctuations. We conclude that the vacuum has a multifractal structure. (orig.)

  5. Probing the topological structure of the QCD vacuum with overlap fermions

    International Nuclear Information System (INIS)

    Ilgenfritz, E.M.; Schierholz, G.; Deutsches Elektronen-Synchrotron; Streuer, T.; Weinberg, V.; Freie Univ. Berlin

    2005-12-01

    Overlap fermions implement exact chiral symmetry on the lattice and are thus an appropriate tool for investigating the chiral and topological structure of the QCD vacuum. We study various chiral and topological aspects on Luescher-Weisz-type quenched gauge field configurations using overlap fermions as a probe. Particular emphasis is placed upon the analysis of the spectral density and the localisation properties of the eigenmodes as well as on the local structure of topological charge fluctuations. (orig.)

  6. Kaon interferometry as signal for the QCD phase transition at RHIC

    International Nuclear Information System (INIS)

    Bernard, S.; Maruhn, J.A.; Greiner, W.; Rischke, D.H.

    1997-01-01

    Pion and kaon correlations in relativistic nuclear collisions are studied in the framework of boost-invariant, cylindrically symmetric hydrodynamics. It is investigated how the inverse widths, R out , R side , of the two-particle correlation functions in out- and side-direction depend on the average transverse momentum K perpendicular to of the particle pair, the initial energy density ε 0 , and the equation of state of the system. The QCD transition leads to a time delay in the expansion of the system and consequently to an enhancement of the ratio R out /R side . This time-delay signal is found to be particularly strong for large average transverse momenta K perpendicular to ∝1 GeV and initial energy densities accessible at RHIC, ε 0 ∝10-20 GeV fm -3 . Neutral kaon pair correlation functions, which are not influenced by final state Coulomb effects and less contaminated by resonance decays than pion correlation functions, seem to be the ideal tool to detect this collective time-delay signature of the QCD transition. (orig.)

  7. An Introduction to Perturbative Methods in Gauge Theories

    International Nuclear Information System (INIS)

    T Muta

    1998-01-01

    This volume develops the techniques of perturbative QCD in great pedagogical detail starting with field theory. Aside from extensive treatments of the renormalization group technique, the operator product expansion formalism and their applications to short-distance reactions, this book provides a comprehensive introduction to gauge theories. Examples and exercises are provided to amplify the discussions on important topics. This is an ideal textbook on the subject of quantum chromodynamics and is essential for researchers and graduate students in high energy physics, nuclear physics and mathematical physics

  8. Investigations of chiral symmetry breaking and topological aspects of lattice QCD

    International Nuclear Information System (INIS)

    Garcia Ramos, Elena

    2013-01-01

    The spontaneous breaking of chiral symmetry is a fascinating phenomenon of QCD whose mechanism is still not well understood and it has fundamental phenomenological implications. It is, for instance, responsible for the low mass of the pions which are effectively Goldstone bosons of the spontaneously broken symmetry. Since these phenomena belong to the low energy regime of QCD, non-perturbative techniques have to be applied in order to study them. In this work we use the twisted mass lattice QCD regularization to compute the chiral condensate, the order parameter of spontaneous chiral symmetry breaking. To this end we apply the recently introduced method of spectral projectors which allows us to perform calculations in large volumes due to its inherently low computational cost. This approach, moreover, enables a direct calculation of the chiral condensate based on a theoretically clean definition of the observable via density chains. We thus present a continuum limit determination of the chirally extrapolated condensate for N f =2 and N f =2+1+1 flavours of twisted mass fermions at maximal twist. In addition we study the chiral behavior of the topological susceptibility, a measure of the topological fluctuations of the gauge fields. We again apply the spectral projector method for this calculation. We comment on the difficulties which appear in the calculation of this observable due to the large autocorrelations involved. Finally we present the continuum limit result of the topological susceptibility in the pure gluonic theory which allows us to perform a test of the Witten-Veneziano relation. We found that this relation is well satisfied. Our results support the validity of the Witten-Veneziano formula which relates the topological fluctuations of the gauge fields with the unexpectedly large value of the η' mass.

  9. Exact mquark ≠ 0 condensates in QCD1+1(NC → ∞)

    International Nuclear Information System (INIS)

    Burkardt, M.

    1994-01-01

    In the limit of an infinite number of colors, we derive an analytic expression for the quark condensation in QCD 1+1 as a function of the quark mass and the gauge coupling constant. For zero quark mass, a nonvanishing quark condensate is obtained. Nevertheless, we prove that there is no phase transition as a function of the quark mass. It is furthermore shown that the expansion of left-angle 0|bar ψψ|0 right-angle in the gauge coupling has zero radius of convergence but that the perturbation series is Borel summable with finite radius of convergence. The nonanalytic behavior m q →0 ∼ -N C √G 2 can only be obtained by summing the perturbation series to infinite order

  10. Flavor-singlet spectrum in multi-flavor QCD

    Energy Technology Data Exchange (ETDEWEB)

    Aoki, Yasamichi; Rinaldi, Enrico

    2017-06-18

    Studying SU(3) gauge theories with increasing number of light fermions is relevant both for understanding the strong dynamics of QCD and for constructing strongly interacting extensions of the Standard Model (e.g. UV completions of composite Higgs models). In order to contrast these many-flavors strongly interacting theories with QCD, we study the flavor-singlet spectrum as an interesting probe. In fact, some composite Higgs models require the Higgs boson to be the lightest flavor-singlet scalar in the spectrum of a strongly interacting new sector with a well defined hierarchy with the rest of the states. Moreover, introducing many light flavors at fixed number of colors can influence the dynamics of the lightest flavor-singlet pseudoscalar. We present the on-going study of these flavor-singlet channels using multiple interpolating operators on high-statistics ensembles generated by the LatKMI collaboration and we compare results with available data obtained by the Lattice Strong Dynamics collaboration. For the theory with 8 flavors, the two collaborations have generated configurations that complement each others with the aim to tackle the massless limit using the largest possible volumes.

  11. Flavor-singlet spectrum in multi-flavor QCD

    Science.gov (United States)

    Aoki, Yasumichi; Aoyama, Tatsumi; Bennett, Ed; Kurachi, Masafumi; Maskawa, Toshihide; Miura, Kohtaroh; Nagai, Kei-ichi; Ohki, Hiroshi; Rinaldi, Enrico; Shibata, Akihiro; Yamawaki, Koichi; Yamazaki, Takeshi

    2018-03-01

    Studying SU(3) gauge theories with increasing number of light fermions is relevant both for understanding the strong dynamics of QCD and for constructing strongly interacting extensions of the Standard Model (e.g. UV completions of composite Higgs models). In order to contrast these many-flavors strongly interacting theories with QCD, we study the flavor-singlet spectrum as an interesting probe. In fact, some composite Higgs models require the Higgs boson to be the lightest flavor-singlet scalar in the spectrum of a strongly interacting new sector with a well defined hierarchy with the rest of the states. Moreover, introducing many light flavors at fixed number of colors can influence the dynamics of the lightest flavor-singlet pseudoscalar. We present the on-going study of these flavor-singlet channels using multiple interpolating operators on high-statistics ensembles generated by the LatKMI collaboration and we compare results with available data obtained by the Lattice Strong Dynamics collaboration. For the theory with 8 flavors, the two collaborations have generated configurations that complement each others with the aim to tackle the massless limit using the largest possible volumes.

  12. Experimental status QCD

    International Nuclear Information System (INIS)

    Radyushkin, A.V.; Slepchenko, L.A.

    1983-01-01

    Analysis of experimental status of quantum chromodynamics (QCD) has been carried out. A short introduction into QCD is given. QCD sum rules are considered. Jets in e + e - annihilation and inclusive processes of lepton-hadron and hadron-hadron scattering are considered. Effect of QCD corrections to perturbation theory on quark count is analyzed

  13. Phase transition over gauge group center and quark confinement in QCD

    International Nuclear Information System (INIS)

    Khokhlachev, S.B.; Makeenko, Yu.N.

    1979-01-01

    A lattice gauge model with the phase transition corresponding to spontaneous breakdown of the group center symmetry is considered. It is shown that the phase diagram, obtained in multicolor case, separates the high and low-temperature phases with confined and nonconfined quarks. The possibility of the Lorentz-invariant continuum limit in the phase with permanently confined quarks is confirmed

  14. Rho meson decay width in SU(2) gauge theories with 2 fundamental flavours

    CERN Document Server

    Janowski, Tadeusz; Pica, Claudio

    2016-01-01

    SU(2) gauge theories with two quark flavours in the fundamental representation are among the most promising theories of composite dynamics describing the electroweak sector. Three out of five Goldstone bosons in these models become the longitudinal components of the W and Z bosons giving them mass. Like in QCD, we expect a spectrum of excitations which appear as resonances in vector boson scattering, in particular the vector resonance corresponding to the rho-meson in QCD. In this talk I will present the preliminary results of the first calculation of the rho-meson decay width in this theory, which is analogous to rho to two pions decay calculation in QCD. The results presented were calculated in a moving frame with total momentum (0,0,1) on two ensembles. Future plans include using 3 moving frames on a larger set of ensembles to extract the resonance parameters more reliably and also take the chiral and continuum limits.

  15. Exclusion of nuclear forces in heavy-ion Coulomb excitation and Coulomb fission experiments

    International Nuclear Information System (INIS)

    Neese, R.E.; Guidry, M.W.

    1982-01-01

    A simple prescription for estimating the energy at which nuclear forces begin to play a role in heavy-ion Coulomb excitation and Coulomb fission experiments is presented. The method differs from most commonly used recipes in accounting for projectile and target nucleus deformation effects. Using a single adjustable parameter the formula reproduces the energy for the onset of Coulomb-nuclear interference effects for a broad range of heavy-ion systems. It is suggested that most Coulomb fission experiments which have been done involve both Coulomb and nuclear excitation processes and should more properly be termed Coulomb-nuclear fission experiments

  16. The Coulomb gap and low energy statistics for Coulomb glasses

    International Nuclear Information System (INIS)

    Glatz, Andreas; Vinokur, Valerii M; Bergli, Joakim; Kirkengen, Martin; Galperin, Yuri M

    2008-01-01

    We study the statistics of local energy minima in the configuration space of two-dimensional lattice Coulomb glasses with site disorder and the behavior of the Coulomb gap depending on the strength of random site energies. At intermediate disorder, i.e., when the typical strength of the disorder is of the same order as the nearest-neighbor Coulomb energy, the high energy tail of the distribution of the local minima is exponential. We furthermore analyze the structure of the local minima and show that most sites of the system have the same occupation numbers in all of these states. The density of states (DOS) shows a transition from the crystalline state at zero disorder (with a hard gap) to an intermediate, probably glassy state with a Coulomb gap. We analyze this Coulomb gap in some detail and show that the DOS deviates slightly from the traditional linear behavior in 2D. For finite systems these intermediate Coulomb gap states disappear for large disorder strengths and only a random localized state in which all electrons are in the minima of the random potential exists. Dedication: This paper is dedicated to Thomas Nattermann, our dearest friend, brilliant colleague, and outstanding teacher

  17. Evaluation of the Coulomb logarithm using cutoff and screened Coulomb interaction potentials

    International Nuclear Information System (INIS)

    Ordonez, C.A.; Molina, M.I.

    1994-01-01

    The Coulomb logarithm is a fundamental plasma parameter which is commonly derived within the framework of the binary collision approximation. The conventional formula for the Coulomb logarithm, λ=ln Λ, takes into account a pure Coulomb interaction potential for binary collisions and is not accurate at small values (λ D in place of λ D (the Debye length) in the conventional formula for the Coulomb logarithm

  18. Investigations in gauge theories, topological solitons and string theories

    International Nuclear Information System (INIS)

    1993-01-01

    This is the Final Report on a supported research project on theoretical particle physics entitled ''Investigations in Gauge Theories, Topological Solitons and String Theories.'' The major theme of particle theory pursued has been within the rubric of the standard model, particularly on the interplay between symmetries and dynamics. Thus, the research has been carried out primarily in the context of gauge with or without chiral fermions and in effective chiral lagrangian field theories. The topics studied include the physical implications of abelian and non-abelian anomalies on the spectrum and possible dynamical symmetry breaking in a wide range of theories. A wide range of techniques of group theory, differential geometry and function theory have been applied to probe topological and conformal properties of quantum field theories in two and higher dimensions, the breaking of global chiral symmetries by vector-like gauge theories such as QCD,the phenomenology of a possibly strongly interacting Higgs sector within the minimal standard model, and the relevance of solitonic ideas to non-perturbative phenomena at SSC energies

  19. Local gauge symmetry and confinement in quantum chromodynamics

    International Nuclear Information System (INIS)

    Bardeen, W.A.; Pearson, R.B.

    1977-01-01

    The nonabelian color gauge theory of quarks and gluons has been proposed as the basis for fundamental theory of hadrons. The features of this theory (quantum chromodynamics) are considered which lead to confinement. A transverse lattice formulation of the theory is also discussed, which is used as a basis for calculation of properties of the hadron bound states. The theory is quantized by eliminating the longitudinal degrees of freedom in favour of coulomb potential. Hadrons are formed as bound states of quarks and the symmetric phase gluons

  20. Low energy gauge couplings in grand unified theories and high precision physics

    International Nuclear Information System (INIS)

    Lynn, B.W.

    1993-09-01

    I generalize the leading log relations between low energy SU(3) QCD , SU(2) rvec I and U(l) Y effective gauge couplings to include all one-loop threshold effects of matter fields in oblique vector self energy quantum corrections for both supersymmetric and non-supersymmetric SU(5) grand unified theories. These always involve an exactly conserved current from the unbroken SU(3) QCD x U(L) QED subgroup; this fact strongly constrains any non-decoupling of heavy states as well as the generic character of threshold effects. Relations between low energy gauge couplings depend on the details of the spectra of both the superheavy and low mass sectors; I display the common origin of the logs appropriate to superheavy matter states, which can be found with well known renormalization group techniques, and the combination of logs and polynomials appropriate for light matter states, which cannot. Relations between any two or all three low energy effective gauge couplings do not depend on the top quark or standard model Higgs' masses. Neither do they depend on neutral color singlet states such as other neutral color singlet Higgs' or higgsinos, neutrinos, zinos or photinos. Further, they do not depend on degenerate SU(5) matter representations, of either spin 0 or spin 1/2 of any mass; matter representations of SU(5) can affect such relations only if there is mass splitting within them. The b quark splitting from the τ and ν τ can affect the relation between gauge couplings for |q 2 | → m b 2 as can hadronic resonances and multi-hadron states for lower |q 2 |. New mass-split representations of light states, such as occur in supersymmetric theories, can also affect such relations

  1. Low energy gauge couplings in grand unified theories and high precision physics

    Energy Technology Data Exchange (ETDEWEB)

    Lynn, B.W. [Stanford Univ., CA (United States). Dept. of Physics]|[Superconducting Super Collider Lab., Dallas, TX (United States)

    1993-09-01

    I generalize the leading log relations between low energy SU(3){sub QCD}, SU(2){sub {rvec I}} and U(l){sub Y} effective gauge couplings to include all one-loop threshold effects of matter fields in oblique vector self energy quantum corrections for both supersymmetric and non-supersymmetric SU(5) grand unified theories. These always involve an exactly conserved current from the unbroken SU(3){sub QCD} {times} U(L){sub QED} subgroup; this fact strongly constrains any non-decoupling of heavy states as well as the generic character of threshold effects. Relations between low energy gauge couplings depend on the details of the spectra of both the superheavy and low mass sectors; I display the common origin of the logs appropriate to superheavy matter states, which can be found with well known renormalization group techniques, and the combination of logs and polynomials appropriate for light matter states, which cannot. Relations between any two or all three low energy effective gauge couplings do not depend on the top quark or standard model Higgs` masses. Neither do they depend on neutral color singlet states such as other neutral color singlet Higgs` or higgsinos, neutrinos, zinos or photinos. Further, they do not depend on degenerate SU(5) matter representations, of either spin 0 or spin 1/2 of any mass; matter representations of SU(5) can affect such relations only if there is mass splitting within them. The b quark splitting from the {tau} and {nu}{sub {tau}} can affect the relation between gauge couplings for {vert_bar}q{sub 2}{vert_bar} {yields} m{sub b}{sup 2} as can hadronic resonances and multi-hadron states for lower {vert_bar}q{sub 2}{vert_bar}. New mass-split representations of light states, such as occur in supersymmetric theories, can also affect such relations.

  2. Convergence of the iterative solution of loop equations in planar QCD2

    International Nuclear Information System (INIS)

    Marchesini, G.; Onofri, E.

    1985-01-01

    A numerical algorithm recently introduced to solve the loop equations in lattice gauge theory is tested on a simple model with a phase transition: the planar limit of QCD in two dimensions. We show that the algorithm reproduces the correct known results in both strong and weak coupling phases, provided that a relaxation parameter a la Gauss-Seidel is introduced in the iteration process. We also give some analytical explanation of the applicability of the method. (orig.)

  3. High-energy effective action from scattering of QCD shock waves

    Energy Technology Data Exchange (ETDEWEB)

    Ian Balitsky

    2005-07-01

    At high energies, the relevant degrees of freedom are Wilson lines - infinite gauge links ordered along straight lines collinear to the velocities of colliding particles. The effective action for these Wilson lines is determined by the scattering of QCD shock waves. I develop the symmetric expansion of the effective action in powers of strength of one of the shock waves and calculate the leading term of the series. The corresponding first-order effective action, symmetric with respect to projectile and target, includes both up and down fan diagrams and pomeron loops.

  4. Double gauge invariance and covariantly-constant vector fields in Weyl geometry

    Science.gov (United States)

    Kassandrov, Vladimir V.; Rizcallah, Joseph A.

    2014-08-01

    The wave equation and equations of covariantly-constant vector fields (CCVF) in spaces with Weyl nonmetricity turn out to possess, in addition to the canonical conformal-gauge, a gauge invariance of another type. On a Minkowski metric background, the CCVF system alone allows us to pin down the Weyl 4-metricity vector, identified herein with the electromagnetic potential. The fundamental solution is given by the ordinary Lienard-Wiechert field, in particular, by the Coulomb distribution for a charge at rest. Unlike the latter, however, the magnitude of charge is necessarily unity, "elementary", and charges of opposite signs correspond to retarded and advanced potentials respectively, thus establishing a direct connection between the particle/antiparticle asymmetry and the "arrow of time".

  5. Consistency questions in the light cone gauge based on equal time commutation rules

    International Nuclear Information System (INIS)

    Haller, K.

    1989-01-01

    We investigate whether time displacement invariant propagators are compatible canonical formulations in the light cone gauge based on equal time commutation rules. We conclude that, in the light cone gauge, time displacement invariant propagators are not consistent with the requirement that, in canonical formulations of gauge theories, only transversely polarized, massless gauge field excitations (photons, or gluons in perturbative QCD), can contribute to the transverse part of a time displacement invariant propagator. When the time displacement invariant light cone gauge propagator is represented as a four-dimensional momentum space Fourier integral the following is observed: Transverse parts of the propagator obtain time displacement invariant contributions from the (k 3 -k 0 ) pole, as well as from the (vertical strokekvertical stroke 2 -k 0 2 ) pole. But since, in the Schroedinger picture (i.e. at t=0), the divergence-free part of the gauge field consists of transversely polarized gauge field excitations only, the transverse part of the propagator either can have time displacement invariant time dependence determined by the (vertical strokekvertical stroke 2 -k 0 2 ) pole; or, if any part of the transverse propagator has time dependence determined by the (k 3 -k 0 ) pole, it cannot be time displacement invariant. (orig.)

  6. Gauge theories in particle physics a practical introduction

    CERN Document Server

    Aitchison, Ian J R

    2013-01-01

    The fourth edition of this well-established, highly regarded two-volume set continues to provide a fundamental introduction to advanced particle physics while incorporating substantial new experimental results, especially in the areas of CP violation and neutrino oscillations. It offers an accessible and practical introduction to the three gauge theories included in the Standard Model of particle physics: quantum electrodynamics (QED), quantum chromodynamics (QCD), and the Glashow-Salam-Weinberg (GSW) electroweak theory. In the first volume, a new chapter on Lorentz transformations and discrete symmetries presents a simple treatment of Lorentz transformations of Dirac spinors. Along with updating experimental results, this edition also introduces Majorana fermions at an early stage, making the material suitable for a first course in relativistic quantum mechanics. Covering much of the experimental progress made in the last ten years, the second volume remains focused on the two non-Abelian quantum gauge field...

  7. QCD as a basis for quark and nuclear forces

    International Nuclear Information System (INIS)

    Close, F.E.

    1983-01-01

    This chapter examines quarks in nucleons and the ideas behind the quantum chromodynamic (QCD) theory of their interactions. Compares nuclei and nucleons, and examines length or energy scales in physics. Reviews the present knowledge about the basic building blocks: quarks and leptons. Discusses color, building colorless hadrons, effects of color inside hadrons (spin flavor correlations, magnetic moments), color as the source of a field theory (molecular and nuclear forces), non-Abelian theories (qualitative features, boson-fermion vertices in SU(N), gauge invariance), renormalization and scaling violation (Lagrangians and renormalization, logs in perturbation theory), and quarks and nuclear forces

  8. 6d, Coulomb branch anomaly matching

    Science.gov (United States)

    Intriligator, Kenneth

    2014-10-01

    6d QFTs are constrained by the analog of 't Hooft anomaly matching: all anomalies for global symmetries and metric backgrounds are constants of RG flows, and for all vacua in moduli spaces. We discuss an anomaly matching mechanism for 6d theories on their Coulomb branch. It is a global symmetry analog of Green-Schwarz-West-Sagnotti anomaly cancellation, and requires the apparent anomaly mismatch to be a perfect square, . Then Δ I 8 is cancelled by making X 4 an electric/magnetic source for the tensor multiplet, so background gauge field instantons yield charged strings. This requires the coefficients in X 4 to be integrally quantized. We illustrate this for theories. We also consider the SCFTs from N small E8 instantons, verifying that the recent result for its anomaly polynomial fits with the anomaly matching mechanism.

  9. B-physics computations from Nf=2 tmQCD

    CERN Document Server

    Carrasco, N.; Dimopoulos, P.; Frezzotti, R.; Gimenez, V.; Herdoiza, G.; Lubicz, V.; Michael, C.; Picca, E.; Rossi, G.C.; Sanfilippo, F.; Shindler, A.; Silvestrini, L.; Simula, S.; Tarantino, C.

    2014-01-01

    We present an accurate lattice QCD computation of the b-quark mass, the B and Bs decay constants, the B-mixing bag-parameters for the full four-fermion operator basis, as well as estimates for \\xi and f_{Bq}\\sqrt{B_q} extrapolated to the continuum limit and the physical pion mass. We have used Nf = 2 dynamical quark gauge configurations at four values of the lattice spacing generated by ETMC. Extrapolation in the heavy quark mass from the charm to the bottom quark region has been carried out using ratios of physical quantities computed at nearby quark masses, having an exactly known infinite mass limit.

  10. Confinement, Chiral Symmetry Breaking and it's Restoration using Dual QCD Formalism

    Directory of Open Access Journals (Sweden)

    Punetha Garima

    2018-01-01

    Full Text Available Utilizing the dual QCD model in term of magnetic symmetry structure of non- Abelian gauge theories, the dynamical chiral-symmetry breaking using Schwinger-Dyson equation has been investigated. A close relation among the color confinement and chiralsymmetry breaking has been observed and demonstrated by computing dynamical parameters. The recovery of the chiral symmetry has also been discussed at finite temperature through the variation of quark mass function and quark condensate which gradually decreases with temperature and vanishes suddenly near the critical temperature.

  11. Numerical studies of QCD renormalons in high-order perturbative expansions

    International Nuclear Information System (INIS)

    Bauer, Clemens

    2013-01-01

    Perturbative expansions in four-dimensional non-Abelian gauge theories such as Quantum Chromodynamics (QCD) are expected to be divergent, at best asymptotic. One reason is that it is impossible to strictly exclude from the relevant Feynman diagrams those energy regions in which a perturbative treatment is inapplicable. The divergent nature of the series is then signaled by a rapid (factorial) growth of the perturbative expansion coefficients, commonly referred to as a renormalon. In QCD, the most severe divergences occur in the infrared (IR) limit and therefore they are classified as IR renormalons. Their appearance can be understood within the well-accepted Operator Product Expansion (OPE) framework. According to the OPE, the perturbative calculation of a physical observable must be amended by non-perturbative power corrections that come in the form of condensates, universal characteristics of the rich QCD vacuum structure. Adding up perturbative and non-perturbative contributions, the ambiguity due to the renormalon cancels and the physical observable is well-defined. Although the field has made considerable progress in the last twenty years, a proof of renormalon existence is still pending. It has only been tested assuming strong simplifications or in toy models. The aim of this thesis is to provide the first numerical evidence for renormalon existence in the gauge sector of QCD. We use Numerical Stochastic Perturbation Theory (NSPT) to directly obtain perturbative coefficients within lattice regularization, a means to replace continuum spacetime by a four-dimensional hypercubic lattice. A peculiar feature of NSPT are comparatively low simulation costs when reaching high expansion orders. We examine two distinct observables: the static self-energy of an isolated quark and the elementary plaquette. Following the OPE classification, the static quark self-energy is ideally suited for a renormalon study. Taking into account peculiarities of the lattice approach such

  12. Colour singlets in perturbative QCD

    International Nuclear Information System (INIS)

    Bassetto, A.

    1979-01-01

    In the axial gauge and at the leading log level, a definite and consistent picture seems to emerge of a parton decay into states in which many partons are found just before confinement should take place. They are grouped into colourless clusters in a number sufficient to exhaust the ''final'' state, still possessing a finite average mass. This result is peculiar of QCD, in particular of its non-abelian nature. Large transverse momenta or more generally average invariant quantities of partons are mainly due to the multiplicities involved in the branching processes. If eventually confinement would convert these clusters into hadrons (and this is of course the main issue which has still to be proven) without a large rearrangement of the colour lines, the picture we have found for colour singlets could apply to the real hadronic world. (author)

  13. Examining the identity of Yukawa with gauge couplings in supersymmetric QCD at LHC

    Energy Technology Data Exchange (ETDEWEB)

    Freitas, A. [Zuerich Univ. (Switzerland). Inst. fuer Theoretische Physik; Skands, P. [Fermi National Accelerator Lab., Batavia, IL (United States); Spira, M. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Zerwas, P.M. [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)

    2007-03-15

    The identity of the quark-squark-gluino Yukawa coupling with the corresponding quark-quark-gluon QCD coupling in supersymmetric theories can be examined experimentally at the Large Hadron Collider (LHC). Extending earlier investigations of like-sign di-lepton final states, we include jets in the analysis of the minimal supersymmetric standard model, adding squark-gluino and gluino-pair production to squark-pair production. Moreover we expand the method towards model-independent analyses which cover more general scenarios. In all cases, squark decays to light charginos and neutralinos persist to play a dominant role. (orig.)

  14. Examining the identity of Yukawa with gauge couplings in supersymmetric QCD at LHC

    Energy Technology Data Exchange (ETDEWEB)

    Freitas, Ayres; /Zurich U.; Skands, Peter Z.; /Fermilab; Spira, M.; /PSI, Villigen; Zerwas, P.M.; /DESY

    2007-03-01

    The identity of the quark-squark-gluino Yukawa coupling with the corresponding quark-quark-gluon QCD coupling in supersymmetric theories can be examined experimentally at the Large Hadron Collider (LHC). Extending earlier investigations of like-sign di-lepton final states, we include jets in the analysis of the minimal supersymmetric standard model, adding squark-gluino and gluino-pair production to squark-pair production. Moreover we expand the method towards model-independent analyses which cover more general scenarios. In all cases, squark decays to light charginos and neutralinos persist to play a dominant role.

  15. Examining the identity of Yukawa with gauge couplings in supersymmetric QCD at LHC

    International Nuclear Information System (INIS)

    Freitas, A.; Spira, M.; Zerwas, P.M.

    2007-03-01

    The identity of the quark-squark-gluino Yukawa coupling with the corresponding quark-quark-gluon QCD coupling in supersymmetric theories can be examined experimentally at the Large Hadron Collider (LHC). Extending earlier investigations of like-sign di-lepton final states, we include jets in the analysis of the minimal supersymmetric standard model, adding squark-gluino and gluino-pair production to squark-pair production. Moreover we expand the method towards model-independent analyses which cover more general scenarios. In all cases, squark decays to light charginos and neutralinos persist to play a dominant role. (orig.)

  16. Extended Hamiltonian formalism of the pure space-like axial gauge Schwinger model

    International Nuclear Information System (INIS)

    Nakawaki, Yuji; Mccartor, Gary

    2001-01-01

    We demonstrate that pure space-like axial gauge quantizations of gauge fields can be constructed in ways that are free from infrared divergences. To do so, we must extend the Hamiltonian formalism to include residual gauge fields. We construct an operator solution and an extended Hamiltonian of the pure space-like axial gauge Schwinger model. We begin by constructing an axial gauge formation in auxiliary coordinates, x μ =(x + , x - ), where x + =x 0 sinθ + x 1 cosθ, x - =x 0 cosθ - x 1 sinθ, and we take A=A 0 cosθ + A 1 sin θ=0 as the gauge fixing condition. In the region 0 - as the evolution parameter and construct a traditional canonical formulation of the temporal gauge Schwinger model in which residual gauge fields dependent only on x + are static canonical variables. Then we extrapolate the temporal gauge operator solution into the axial region, π / 4 + is taken as the evolution parameter. In the axial region we find that we have to take the representation of the residual gauge fields realizing the Mandelstam-Leibbrandt prescription in order for the infrared divergences resulting from (∂) -1 to be canceled by corresponding ones resulting from the inverse of the hyperbolic Laplace operator. We overcome the difficulty of constructing the Hamiltonian for the residual gauge fields by employing McCartor and Robertson's method, which gives us a term integrated over x - =constant. Finally, by taking the limit θ→π / 2 - 0, we obtain an operator solution and the Hamiltonian of the axial gauge (Coulomb gauge) Schwinger model in ordinary coordinates. That solution includes auxiliary fields, and the representation space is of indefinite metric, providing further evidence that 'physical' gauges are no more physical than 'unphysical' gauges. (author)

  17. Foundations of quantum chromodynamics: Perturbative methods in gauge theories

    International Nuclear Information System (INIS)

    Muta, T.

    1986-01-01

    This volume develops the techniques of perturbative QCD in great detail starting with field theory. Aside from extensive treatments of the renormalization group technique, the operator product expansion formalism and their applications to short-distance reactions, this book provides a comprehensive introduction to gauge field theories. Examples and exercises are provided to amplify the discussions on important topics. Contents: Introduction; Elements of Quantum Chromodynamics; The Renormalization Group Method; Asymptotic Freedom; Operator Product Expansion Formalism; Applications; Renormalization Scheme Dependence; Factorization Theorem; Further Applications; Power Corrections; Infrared Problem. Power Correlations; Infrared Problem

  18. Status and future of lattice gauge theory

    International Nuclear Information System (INIS)

    Hoek, J.

    1989-07-01

    The current status of lattice Quantum Chromo Dynamics (QCD) calculations, the computer requirements to obtain physical results and the direction computing is taking are described. First of all, there is a lot of evidence that QCD is the correct theory of strong interactions. Since it is an asymptotically free theory we can use perturbation theory to solve it in the regime of very hard collisions. However even in the case of very hard parton collisions the end-results of the collisions are bound states of quarks and perturbation theory is not sufficient to calculate these final stages. The way to solve the theory in this regime was opened by Wilson. He contemplated replacing the space-time continuum by a discrete lattice, with a lattice spacing a. Continuum physics is then recovered in the limit where the correlation length of the theory, say ξ. is large with respect to the lattice spacing. This will be true if the lattice spacing becomes very small, which for asymptotically free theories also implies that the coupling g becomes small. The lattice approach to QCD is in many respects analogous to the use of finite element methods to solve classical field theories. These finite element methods are easy to apply in 2-dimensional simulations but are computationally demanding in the 3-dimensional case. Therefore it is not unexpected that the 4-dimensional simulations needed for lattice gauge theories have led to an explosion in demand for computing power by theorists. (author)

  19. Non-Perturbative QCD Coupling and Beta Function from Light Front Holography

    International Nuclear Information System (INIS)

    Brodsky, Stanley J.

    2010-01-01

    The light-front holographic mapping of classical gravity in AdS space, modified by a positive-sign dilaton background, leads to a non-perturbative effective coupling α s AdS (Q 2 ). It agrees with hadron physics data extracted from different observables, such as the effective charge defined by the Bjorken sum rule, as well as with the predictions of models with built-in confinement and lattice simulations. It also displays a transition from perturbative to nonperturbative conformal regimes at a momentum scale ∼ 1 GeV. The resulting β-function appears to capture the essential characteristics of the full β-function of QCD, thus giving further support to the application of the gauge/gravity duality to the confining dynamics of strongly coupled QCD. Commensurate scale relations relate observables to each other without scheme or scale ambiguity. In this paper we extrapolate these relations to the nonperturbative domain, thus extending the range of predictions based on α s AdS (Q 2 ).

  20. Exponential noise reduction in Lattice QCD: new tools for new physics

    CERN Multimedia

    CERN. Geneva

    2017-01-01

    The numerical computations of many quantities of theoretical and phenomenological interest are plagued by statistical errors which increase exponentially with the distance of the sources in the relevant correlators. Notable examples are baryon masses and matrix elements, the hadronic vacuum polarization and the light-by-light scattering contributions to the muon g-2, and the form factors of semileptonic B decays. Reliable and precise determinations of these quantities are very difficult if not impractical with state-of-the-art standard Monte Carlo integration schemes. I will discuss a recent proposal for factorizing the fermion determinant in lattice QCD that leads to a local action in the gauge field and in the auxiliary boson fields. Once combined with the corresponding factorization of the quark propagator, it paves the way for multi-level Monte Carlo integration in the presence of fermions opening new perspectives in lattice QCD and in its capability to unveil new physics. Exploratory results on the impac...

  1. Determination of csw in Nf=3+1 lattice QCD with massive Wilson fermions

    International Nuclear Information System (INIS)

    Fritzsch, Patrick; Stollenwerk, Felix; Wolff, Ulli; Sommer, Rainer

    2015-01-01

    We develop a strategy for the non-perturbative determination of the O(a)-improvement coefficient c sw for Wilson fermions with massive sea quarks. The improvement condition is defined via the PCAC relation in the Schroedinger functional. It is imposed along a line of constant physics designed to be close to the correct mass of the charm quark. The numerical work uses the tree-level improved Luescher-Weisz gauge action in N f =3+1 Lattice QCD.

  2. Integrands for QCD rational terms and {N} = {4} SYM from massive CSW rules

    Science.gov (United States)

    Elvang, Henriette; Freedman, Daniel Z.; Kiermaier, Michael

    2012-06-01

    We use massive CSW rules to derive explicit compact expressions for integrands of rational terms in QCD with any number of external legs. Specifically, we present all- n integrands for the one-loop all-plus and one-minus gluon amplitudes in QCD. We extract the finite part of spurious external-bubble contributions systematically; this is crucial for the application of integrand-level CSW rules in theories without supersymmetry. Our approach yields integrands that are independent of the choice of CSW reference spinor even before integration. Furthermore, we present a recursive derivation of the recently proposed massive CSW-style vertex expansion for massive tree amplitudes and loop integrands on the Coulomb-branch of {N} = {4} SYM. The derivation requires a careful study of boundary terms in all-line shift recursion relations, and provides a rigorous (albeit indirect) proof of the recently proposed construction of massive amplitudes from soft-limits of massless on-shell amplitudes. We show that the massive vertex expansion manifestly preserves all holomorphic and half of the anti-holomorphic supercharges, diagram-by-diagram, even off-shell.

  3. Polarisation of electroweak gauge bosons at the LHC

    Directory of Open Access Journals (Sweden)

    Vryonidou Eleni

    2013-05-01

    Full Text Available We present results for the polarisation of gauge bosons produced at the LHC. Polarisation effects for W bosons manifest themselves in the angular distributions of the lepton and in the distributions of lepton transverse momentum and missing transverse energy. The polarisation is discussed for a range of different processes producing W bosons such as W+jets and W from top production. The relative contributions of the different polarisation states vary from process to process, reflecting the dynamics of the underlying hardscattering process. We also calculate the polarisation of the Z boson produced in association with QCD jets at the LHC.

  4. QCD-instantons at LHC. Theoretical aspects

    International Nuclear Information System (INIS)

    Petermann, M.

    2007-06-01

    Instantons are nonperturbative, topologically nontrivial field configurations, which occur in every nonabelian gauge theory. They can be understood as tunneling processes between topologically distinct vacua. Although being a basic theoretical aspect of the Standard Model, a direct experimental verification of instanton processes is still lacking. In this thesis the general discovery potential for QCD-instantons at the LHC is studied in detail by means of instanton perturbation theory. In this context the close correspondence between the leading instanton induced processes at HERA and at LHC becomes important. Essential aspects and differences to deep inelastic scattering can already be revealed by studying the simplest process. Based on these results inclusive cross sections are calculated including the emission of final state gluons. Compared to deep inelastic scattering, a large enhancement of the cross section is found. (orig.)

  5. National software infrastructure for lattice gauge theory

    International Nuclear Information System (INIS)

    Brower, Richard C

    2005-01-01

    The current status of the SciDAC software infrastructure project for lattice gauge theory is summarized. This includes the the design of a QCD application programmers interface (API) that allows existing and future codes to be run efficiently on Terascale hardware facilities and to be rapidly ported to new dedicated or commercial platforms. The critical components of the API have been implemented and are in use on the US QCDOC hardware at BNL and on both the switched and mesh architecture Pentium 4 clusters at Fermi National Accelerator Laboratory (FNAL) and Thomas Jefferson National Accelerator Facility (JLab). Future software infrastructure requirements and research directions are also discussed

  6. BPS/CFT Correspondence III: Gauge Origami Partition Function and qq-Characters

    Science.gov (United States)

    Nekrasov, Nikita

    2018-03-01

    We study generalized gauge theories engineered by taking the low energy limit of the Dp branes wrapping {X × {T}^{p-3}}, with X a possibly singular surface in a Calabi-Yau fourfold Z. For toric Z and X the partition function can be computed by localization, making it a statistical mechanical model, called the gauge origami. The random variables are the ensembles of Young diagrams. The building block of the gauge origami is associated with a tetrahedron, whose edges are colored by vector spaces. We show the properly normalized partition function is an entire function of the Coulomb moduli, for generic values of the {Ω} -background parameters. The orbifold version of the theory defines the qq-character operators, with and without the surface defects. The analytic properties are the consequence of a relative compactness of the moduli spaces M({ěc n}, k) of crossed and spiked instantons, demonstrated in "BPS/CFT correspondence II: instantons at crossroads, moduli and compactness theorem".

  7. Mirror symmetry in three-dimensional gauge theories, quivers and D-branes

    International Nuclear Information System (INIS)

    De Boer, J.; Ernest Orlando Lawrence Berkeley Nat. Lab., CA; Hori, K.; Ernest Orlando Lawrence Berkeley Nat. Lab., CA; Ooguri, H.; Ernest Orlando Lawrence Berkeley Nat. Lab., CA; Oz, Y.; Ernest Orlando Lawrence Berkeley Nat. Lab., CA

    1997-01-01

    We construct and analyze dual N=4 supersymmetric gauge theories in three dimensions with unitary and symplectic gauge groups. The gauge groups and the field content of the theories are encoded in quiver diagrams. The duality exchanges the Coulomb and Higgs branches and the Fayet-Iliopoulos and mass parameters. We analyze the classical and the quantum moduli spaces of the theories and construct an explicit mirror map between the mass parameters and the Fayet-Iliopoulos parameters of the dual. The results generalize the relation between ALE spaces and moduli spaces of SU(n) and SO(2n) instantons. We interpret some of these results from the string theory viewpoint, for SU(n) by analyzing T-duality and extremal transitions in type II string compactifications, for SO(2n) by using D-branes as probes. Finally, we make a proposal for the moduli space of vacua of these theories in the absence of matter. (orig.)

  8. Fuzzy bags, Polyakov loop and gauge/string duality

    Directory of Open Access Journals (Sweden)

    Zuo Fen

    2014-01-01

    Full Text Available Confinement in SU(N gauge theory is due to the linear potential between colored objects. At short distances, the linear contribution could be considered as the quadratic correction to the leading Coulomb term. Recent lattice data show that such quadratic corrections also appear in the deconfined phase, in both the thermal quantities and the Polyakov loop. These contributions are studied systematically employing the gauge/string duality. “Confinement” in N${\\cal N}$ = 4 SU(N Super Yang-Mills (SYM theory could be achieved kinematically when the theory is defined on a compact space manifold. In the large-N limit, deconfinement of N${\\cal N}$ = 4 SYM on S3${{\\Bbb S}^3}$ at strong coupling is dual to the Hawking-Page phase transition in the global Anti-de Sitter spacetime. Meantime, all the thermal quantities and the Polyakov loop achieve significant quadratic contributions. Similar results can also be obtained at weak coupling. However, when confinement is induced dynamically through the local dilaton field in the gravity-dilaton system, these contributions can not be generated consistently. This is in accordance with the fact that there is no dimension-2 gauge-invariant operator in the boundary gauge theory. Based on these results, we suspect that quadratic corrections, and also confinement, should be due to global or non-local effects in the bulk spacetime.

  9. Coulomb interaction in multiple scattering theory

    International Nuclear Information System (INIS)

    Ray, L.; Hoffmann, G.W.; Thaler, R.M.

    1980-01-01

    The treatment of the Coulomb interaction in the multiple scattering theories of Kerman-McManus-Thaler and Watson is examined in detail. By neglecting virtual Coulomb excitations, the lowest order Coulomb term in the Watson optical potential is shown to be a convolution of the point Coulomb interaction with the distributed nuclear charge, while the equivalent Kerman-McManus-Thaler Coulomb potential is obtained from an averaged, single-particle Coulombic T matrix. The Kerman-McManus-Thaler Coulomb potential is expressed as the Watson Coulomb term plus additional Coulomb-nuclear and Coulomb-Coulomb cross terms, and the omission of the extra terms in usual Kerman-McManus-Thaler applications leads to negative infinite total reaction cross section predictions and incorrect pure Coulomb scattering limits. Approximations are presented which eliminate these anomalies. Using the two-potential formula, the full projectile-nucleus T matrix is separated into two terms, one resulting from the distributed nuclear charge and the other being a Coulomb distorted nuclear T matrix. It is shown that the error resulting from the omission of the Kerman-McManus-Thaler Coulomb terms is effectively removed when the pure Coulomb T matrix in Kerman-McManus-Thaler is replaced by the analogous quantity in the Watson approach. Using the various approximations, theoretical angular distributions are obtained for 800 MeV p+ 208 Pb elastic scattering and compared with experimental data

  10. Lattice QCD calculations on commodity clusters at DESY

    International Nuclear Information System (INIS)

    Gellrich, A.; Pop, D.; Wegner, P.; Wittig, H.; Hasenbusch, M.; Jansen, K.

    2003-06-01

    Lattice Gauge Theory is an integral part of particle physics that requires high performance computing in the multi-Tflops regime. These requirements are motivated by the rich research program and the physics milestones to be reached by the lattice community. Over the last years the enormous gains in processor performance, memory bandwidth, and external I/O bandwidth for parallel applications have made commodity clusters exploiting PCs or workstations also suitable for large Lattice Gauge Theory applications. For more than one year two clusters have been operated at the two DESY sites in Hamburg and Zeuthen, consisting of 32 resp. 16 dual-CPU PCs, equipped with Intel Pentium 4 Xeon processors. Interconnection of the nodes is done by way of Myrinet. Linux was chosen as the operating system. In the course of the projects benchmark programs for architectural studies were developed. The performance of the Wilson-Dirac Operator (also in an even-odd preconditioned version) as the inner loop of the Lattice QCD (LQCD) algorithms plays the most important role in classifying the hardware basis to be used. Using the SIMD streaming extensions (SSE/SSE2) on Intel's Pentium 4 Xeon CPUs give promising results for both the single CPU and the parallel version. The parallel performance, in addition to the CPU power and the memory throughput, is nevertheless strongly influenced by the behavior of hardware components like the PC chip-set and the communication interfaces. The paper starts by giving a short explanation about the physics background and the motivation for using PC clusters for Lattice QCD. Subsequently, the concept, implementation, and operating experiences of the two clusters are discussed. Finally, the paper presents benchmark results and discusses comparisons to systems with different hardware components including Myrinet-, GigaBit-Ethernet-, and Infiniband-based interconnects. (orig.)

  11. The topological long range order in QCD. Applications to heavy ion collisions and cosmology

    Directory of Open Access Journals (Sweden)

    Zhitnitsky Ariel R.

    2015-01-01

    Full Text Available We argue that the local violation of P invariance in heavy ion collisions is a consequence of the long range topological order which is inherent feature of strongly coupled QCD. A similar phenomenon is known to occur in some topologically ordered condensed matter systems with a gap. We also discuss possible cosmological applications of this long range order in strongly coupled gauge theories. In particular, we argue that the de Sitter behaviour might be dynamically generated as a result of the long range order. In this framework the inflaton is an auxiliary field which effectively describes the dynamics of topological sectors in a gauge theory in the expanding universe, rather than a new dynamical degree of freedom.

  12. On the independent particle approximation of Gauge theories: a simple example

    International Nuclear Information System (INIS)

    Palladino, B.E.

    1992-08-01

    In this work, the independent particle model formulation is studied as a mean-field approximation of gauge theories using the path integral approach in the framework of quantum electrodynamics in 1+1 dimensions. It is shown how a mean-field approximation scheme can be applied to fit an effective potential to an independent particle model, building a straightforward relation between the model and the associated gauge field theory. An example is made considering the problem of massive Dirac fermions on a line, the so called massive Schwinger model. An interesting result is found, indicating a behaviour of screening of the charges in the relativistic limit of strong coupling. A forthcoming application of the method developed to confining potentials in independent quark models for QCD is in view and is briefly discussed. (author)

  13. SU(N) instantons in the field strength approach to QCD

    International Nuclear Information System (INIS)

    Reinhardt, H.

    1994-01-01

    Field strength formulated Yang-Mills theory is confronted to the traditional formulation in terms of gauge fields. It is shown that both formulations yield the same semiclassics, in particular the same instanton physics. The field strength formulation is, however, superior at the tree level where it includes already a good deal of quantum fluctuations of the standard formulation. These quantum fluctuations break the scale invariance of classical QCD and give rise to an instanton interaction. The latter causes the instanton to condense and to form a homogeneous instanton solid. These instanton solids show up in the field strength approach as homogeneous (constant up to gauge transformations) vacuum solutions. A new class of SU(N) instantons is presented which are not embeddings of SU(N-1) instantons but have non-trivial SU(N) color structure and carry winding number n = N/(N 2 -1)/6. These novel instantons generate (after condensation) the lowest action homogeneous solutions of the field strength approach. (orig.)

  14. High temperature QCD with three flavors of improved staggered quarks

    International Nuclear Information System (INIS)

    Bernard, C.; Burch, T.; Tar, C.E. de; Gottlieb, Steven; Gregory, Eric; Heller, U.M.; Osborn, J.; Sugar, R.L.; Toussaint, D.

    2003-01-01

    We present an update of our study of high temperature QCD with three flavors of quarks, using a Symanzik improved gauge action and the Asqtad staggered quark action. Simulations are being carried out on lattices with N t = 4, 6 and 8 for the case of three degenerate quarks with masses less than or equal to the strange quark mass, m s and on lattices with N t = 6 and 8 for degenerate up and down quarks with masses in the range 0.2m s ≤ m u,d ≤ 0.6m s and the strange quark fixed near its physical value. We also report on first computations of quark number susceptibilities with the Asqtad action. These susceptibilities are of interest because they can be related to event-by-event fluctuations in heavy ion collision experiments. Use of the improved quark action leads to a substantial reduction in lattice artifacts. This can be seen already for free fermions and carries over into our results for QCD

  15. Baryon interactions from lattice QCD with physical quark masses - Nuclear forces and ΞΞ forces -

    Science.gov (United States)

    Doi, Takumi; Iritani, Takumi; Aoki, Sinya; Gongyo, Shinya; Hatsuda, Tetsuo; Ikeda, Yoichi; Inoue, Takashi; Ishii, Noriyoshi; Miyamoto, Takaya; Nemura, Hidekatsu; Sasaki, Kenji

    2018-03-01

    We present the latest lattice QCD results for baryon interactions obtained at nearly physical quark masses. Nf = 2 + 1 nonperturbatively O(a)-improved Wilson quark action with stout smearing and Iwasaki gauge action are employed on the lattice of (96a)4 ≃(8.1fm)4 with a-1 ≃2.3 GeV, where mπ ≃146 MeV and mK ≃525 MeV. In this report, we study the two-nucleon systems and two-Ξ systems in 1S0 channel and 3S1-3D1 coupled channel, and extract central and tensor interactions by the HAL QCD method. We also present the results for the NΩ interaction in 5S2 channel which is relevant to the NΩ pair-momentum correlation in heavy-ion collision experiments.

  16. ΛcN interaction from lattice QCD and its application to Λc hypernuclei

    Science.gov (United States)

    Miyamoto, Takaya; Aoki, Sinya; Doi, Takumi; Gongyo, Shinya; Hatsuda, Tetsuo; Ikeda, Yoichi; Inoue, Takashi; Iritani, Takumi; Ishii, Noriyoshi; Kawai, Daisuke; Murano, Keiko; Nemura, Hidekatsu; Sasaki, Kenji

    2018-03-01

    The interaction between Λc and a nucleon (N) is investigated by employing the HAL QCD method in the (2 + 1)-flavor lattice QCD on a (2.9fm) 3 volume at mπ ≃ 410 , 570 , 700 MeV. We study the central potential in S10 channel as well as central and tensor potentials in S31-3D1 channel, and find that the tensor potential for Λc N is negligibly weak and central potentials in both S10 and S31-3D1 channels are almost identical with each other except at short distances. Phase shifts and scattering lengths calculated with these potentials show that the interaction of Λc N system is attractive and has a similar strength in S10 and S31 channels at low energies (i.e. the kinetic energy less than about 40 MeV). While the attractions are not strong enough to form two-body bound states, our results lead to a possibility to form Λc hypernuclei for sufficiently large atomic numbers (A). To demonstrate this, we derive a single-folding potential for Λc hypernuclei from the Λc-nucleon potential obtained in lattice QCD, and find that Λc hypernuclei can exist for A ≥ 12 with the binding energies of a few MeV. We also estimate the Coulomb effect for the Λc hypernuclei.

  17. A Conclusive Test of Abelian Dominance Hypothesis for Topological Charge in the QCD Vacuum

    OpenAIRE

    Sasaki, Shoichi; Miyamura, Osamu

    1998-01-01

    We study the topological feature in the QCD vacuum based on the hypothesis of abelian dominance. The topological charge $Q_{\\rm SU(2)}$ can be explicitly represented in terms of the monopole current in the abelian dominated system. To appreciate its justification, we directly measure the corresponding topological charge $Q_{\\rm Mono}$, which is reconstructed only from the monopole current and the abelian component of gauge fields, by using the Monte Carlo simulation on SU(2) lattice. We find ...

  18. From the Dyson-Schwinger to the Transport Equation in the Background Field Gauge of QCD

    CERN Document Server

    Wang, Q; Stöcker, H; Greiner, W

    2003-01-01

    The non-equilibrium quantum field dynamics is usually described in the closed-time-path formalism. The initial state correlations are introduced into the generating functional by non-local source terms. We propose a functional approach to the Dyson-Schwinger equation, which treats the non-local and local source terms in the same way. In this approach, the generating functional is formulated for the connected Green functions and one-particle-irreducible vertices. The great advantages of our approach over the widely used two-particle-irreducible method are that it is much simpler and that it is easy to implement the procedure in a computer program to automatically generate the Feynman diagrams for a given process. The method is then applied to a pure gluon plasma to derive the gauge-covariant transport equation from the Dyson-Schwinger equation in the background covariant gauge. We discuss the structure of the kinetic equation and show its relationship with the classical one. We derive the gauge-covariant colli...

  19. Introduction to lattice gauge theory

    International Nuclear Information System (INIS)

    Gupta, R.

    1987-01-01

    The lattice formulation of Quantum Field Theory (QFT) can be exploited in many ways. We can derive the lattice Feynman rules and carry out weak coupling perturbation expansions. The lattice then serves as a manifestly gauge invariant regularization scheme, albeit one that is more complicated than standard continuum schemes. Strong coupling expansions: these give us useful qualitative information, but unfortunately no hard numbers. The lattice theory is amenable to numerical simulations by which one calculates the long distance properties of a strongly interacting theory from first principles. The observables are measured as a function of the bare coupling g and a gauge invariant cut-off ≅ 1/α, where α is the lattice spacing. The continuum (physical) behavior is recovered in the limit α → 0, at which point the lattice artifacts go to zero. This is the more powerful use of lattice formulation, so in these lectures the author focuses on setting up the theory for the purpose of numerical simulations to get hard numbers. The numerical techniques used in Lattice Gauge Theories have their roots in statistical mechanics, so it is important to develop an intuition for the interconnection between quantum mechanics and statistical mechanics. This will be the emphasis of the first lecture. In the second lecture, the author reviews the essential ingredients of formulating QCD on the lattice and discusses scaling and the continuum limit. In the last lecture the author summarizes the status of some of the main results. He also mentions the bottlenecks and possible directions for research. 88 refs

  20. The QCD mass gap and quark deconfinement scales as mass bounds in strong gravity

    Energy Technology Data Exchange (ETDEWEB)

    Burikham, Piyabut [Chulalongkorn University, High Energy Physics Theory Group, Department of Physics, Faculty of Science, Bangkok (Thailand); Harko, Tiberiu [Babes-Bolyai University, Department of Physics, Cluj-Napoca (Romania); University College London, Department of Mathematics, London (United Kingdom); Lake, Matthew J. [Sun Yat-Sen University, School of Physics, Guangzhou (China); Nanyang Technological University, School of Physical and Mathematical Sciences, Singapore (Singapore); Naresuan University, The Institute for Fundamental Study, ' ' The Tah Poe Academia Institute' ' , Phitsanulok (Thailand); Thailand Center of Excellence in Physics, Ministry of Education, Bangkok (Thailand)

    2017-11-15

    Though not a part of mainstream physics, Salam's theory of strong gravity remains a viable effective model for the description of strong interactions in the gauge singlet sector of QCD, capable of producing particle confinement and asymptotic freedom, but not of reproducing interactions involving SU(3) color charge. It may therefore be used to explore the stability and confinement of gauge singlet hadrons, though not to describe scattering processes that require color interactions. It is a two-tensor theory of both strong interactions and gravity, in which the strong tensor field is governed by equations formally identical to the Einstein equations, apart from the coupling parameter, which is of order 1 GeV{sup -1}. We revisit the strong gravity theory and investigate the strong gravity field equations in the presence of a mixing term which induces an effective strong cosmological constant, Λ{sub f}. This introduces a strong de Sitter radius for strongly interacting fermions, producing a confining bubble, which allows us to identify Λ{sub f} with the 'bag constant' of the MIT bag model, B ≅ 2 x 10{sup 14} g cm{sup -3}. Assuming a static, spherically symmetric geometry, we derive the strong gravity TOV equation, which describes the equilibrium properties of compact hadronic objects. From this, we determine the generalized Buchdahl inequalities for a strong gravity 'particle', giving rise to upper and lower bounds on the mass/radius ratio of stable, compact, strongly interacting objects. We show, explicitly, that the existence of the lower mass bound is induced by the presence of Λ{sub f}, producing a mass gap, and that the upper bound corresponds to a deconfinement phase transition. The physical implications of our results for holographic duality in the context of the AdS/QCD and dS/QCD correspondences are also discussed. (orig.)

  1. Relating hard QCD processes through universality of mass singularities

    International Nuclear Information System (INIS)

    Amati, D.; Petronzio, R.; Veneziano, G.

    1978-01-01

    Hard QCD processes involving final jets are studied and compared by means of a simple approach to mass singularities. This is based on the Lee-Nauenberg-Kinoshita theorem and on a rather subtle use of gauge invariance in hard collinear gluon bremsstrahlung. One-loop results are easily derived for processes involving any number of initial quarks and/or currents. The method greatly simplifies the computation of higher-order loops at the leading log level and the preliminary results allow one to conclude that the crucial features encountered at the one-loop level will persist. The authors are thus able to relate different hard processes and to show that suitable ratios of cross sections, being free from mass singularities, can be computed perturbatively, as usually assumed in QCD-inspired parton models. It is also possible to relate the universal leading mass singularities to leading scaling violations and to extend therefor the results of the operator product expansion method to processes outside the range of the light-cone analysis. Some delicate points caused by confinement-related singularities (e.g. narrow resonance poles) are also discussed. (Auth.)

  2. The role of instantons in scale-invariant gauge theories

    International Nuclear Information System (INIS)

    Affleck, I.

    1980-01-01

    Instanton calculations in scale-invariant gauge theories, such as QCD, have long been plagued by divergences at large distances where strong coupling effects are important. Furthermore, Witten has argued that quantum effects may cause the instanton gas to disappear and has displayed this phenomenon in the CPsup(N-1) model at large N. It is argued here that instantons can play a role in calculations involving an inherent infrared cut-off, and this is demonstrated in the CPsup(N-1) model for large N at a finite temperature. Some results on finite-temperature QED are also obtained in passing. (orig.)

  3. QCD corrections to $e^{+} e^{-} \\to u \\overline {d} s \\overline {c}$ at LEP 2 and the Next Linear Collider CC11 at O $\\alpha_{s}$

    CERN Document Server

    Maina, E; Pizzio, M

    1998-01-01

    QCD one-loop corrections to the full gauge invariant set of electroweak diagrams describing the hadronic process $e^+ e^- \\to u~\\bar d~s~\\bar c$ are computed. Four-jet shape variables for $WW$ events are studied at next-to-leading order and the effects of QCD corrections on the determination of the $W$--mass in the hadronic channel at Lep 2 and NLC is discussed. We compare the exact calculation with a ``naive''approach to strong radiative corrections which has been widely used in the literature.

  4. Electron transport in gold colloidal nanoparticle-based strain gauges

    Science.gov (United States)

    Moreira, Helena; Grisolia, Jérémie; Sangeetha, Neralagatta M.; Decorde, Nicolas; Farcau, Cosmin; Viallet, Benoit; Chen, Ke; Viau, Guillaume; Ressier, Laurence

    2013-03-01

    A systematic approach for understanding the electron transport mechanisms in resistive strain gauges based on assemblies of gold colloidal nanoparticles (NPs) protected by organic ligands is described. The strain gauges were fabricated from parallel micrometer wide wires made of 14 nm gold (Au) colloidal NPs on polyethylene terephthalate substrates, elaborated by convective self-assembly. Electron transport in such devices occurs by inter-particle electron tunneling through the tunnel barrier imposed by the organic ligands protecting the NPs. This tunnel barrier was varied by changing the nature of organic ligands coating the nanoparticles: citrate (CIT), phosphines (BSPP, TDSP) and thiols (MPA, MUDA). Electro-mechanical tests indicate that only the gold NPs protected by phosphine and thiol ligands yield high gauge sensitivity. Temperature-dependent resistance measurements are explained using the ‘regular island array model’ that extracts transport parameters, i.e., the tunneling decay constant β and the Coulomb charging energy EC. This reveals that the Au@CIT nanoparticle assemblies exhibit a behavior characteristic of a strong-coupling regime, whereas those of Au@BSPP, Au@TDSP, Au@MPA and Au@MUDA nanoparticles manifest a weak-coupling regime. A comparison of the parameters extracted from the two methods indicates that the most sensitive gauges in the weak-coupling regime feature the highest β. Moreover, the EC values of these 14 nm NPs cannot be neglected in determining the β values.

  5. Prospects for gauge theories

    International Nuclear Information System (INIS)

    Bailin, D.

    1980-01-01

    The author reviews the present status of the standard model of weak and electromagnetic interactions and of QCD and examines the likely avenues of future development. The most attractive possibility is that there is a ''grand unified theory'' (GUT) which describes all known interactions except gravity, and in which the only input energy scale is the Planck mass. The GUTs so far proposed share the deficiency that they offer no explanation of the (>=3) observed fermion generations. The author reviews the 'horizontal' symmetries invented to bring order to the fermion sector. Typically such theories have non-minimal Higgs content, so he reviews the processes whereby charged or neutral scalars may be found. The incorporation of supersymmetry into the gauge theory of strong, weak and electromagnetic interactions is another attractive prospect and he discusses briefly the attempts to do this and the likely experimental signatures of such a scheme. (Auth.)

  6. Investigating Coulomb's Law.

    Science.gov (United States)

    Noll, Ellis; Koehlinger, Mervin; Kowalski, Ludwik; Swackhamer, Gregg

    1998-01-01

    Describes the use of a computer-linked camera to demonstrate Coulomb's law. Suggests a way of reducing the difficulties in presenting Coulomb's law by teaching the inverse square law of gravity and the inverse square law of electricity in the same unit. (AIM)

  7. Exceptional thermodynamics. The equation of state of G2 gauge theory

    International Nuclear Information System (INIS)

    Bruno, Mattia; Panero, Marco; Pellegrini, Roberto

    2014-10-01

    We present a lattice study of the equation of state in Yang-Mills theory based on the exceptional G 2 gauge group. As is well-known, at zero temperature this theory shares many qualitative features with real-world QCD, including the absence of colored states in the spectrum and dynamical string breaking at large distances. In agreement with previous works, we show that at finite temperature this theory features a first-order deconfining phase transition, whose nature can be studied by a semi-classical computation. We also show that the equilibrium thermodynamic observables in the deconfined phase bear striking quantitative similarities with those found in SU(N) gauge theories: in particular, these quantities exhibit nearly perfect proportionality to the number of gluon degrees of freedom, and the trace anomaly reveals a characteristic quadratic dependence on the temperature, also observed in SU(N) Yang-Mills theories (both in four and in three spacetime dimensions). We compare our lattice data with analytical predictions from effective models, and discuss their implications for the deconfinement mechanism and high-temperature properties of strongly interacting, non-supersymmetric gauge theories. Our results give strong evidence for the conjecture that the thermal deconfining transition is governed by a universal mechanism, common to all simple gauge groups.

  8. Finite-temperature phase structure of lattice QCD with Wilson quark action

    International Nuclear Information System (INIS)

    Aoki, S.; Ukawa, A.; Umemura, T.

    1996-01-01

    The long-standing issue of the nature of the critical line of lattice QCD with the Wilson quark action at finite temperatures, defined to be the line of vanishing pion screening mass, and its relation to the line of finite-temperature chiral transition is examined. Presented are both analytical and numerical evidence that the critical line forms a cusp at a finite gauge coupling, and that the line of chiral transition runs past the tip of the cusp without touching the critical line. Implications on the continuum limit and the flavor dependence of chiral transition are discussed. copyright 1996 The American Physical Society

  9. Exclusive radiative decays of W and Z bosons in QCD factorization

    Energy Technology Data Exchange (ETDEWEB)

    Grossman, Yuval [Department of Physics, LEPP, Cornell University,Ithaca, NY 14853 (United States); König, Matthias [PRISMA Cluster of Excellence & Mainz Institute for Theoretical Physics,Johannes Gutenberg University,55099 Mainz (Germany); Neubert, Matthias [Department of Physics, LEPP, Cornell University,Ithaca, NY 14853 (United States); PRISMA Cluster of Excellence & Mainz Institute for Theoretical Physics,Johannes Gutenberg University,55099 Mainz (Germany)

    2015-04-20

    We present a detailed theoretical analysis of very rare, exclusive hadronic decays of the electroweak gauge bosons V=W,Z from first principles of QCD. Our main focus is on the radiative decays V→Mγ, in which M is a pseudoscalar or vector meson. At leading order in an expansion in powers of Λ{sub QCD}/m{sub V} the decay amplitudes can be factorized into convolutions of calculable hard-scattering coefficients with the leading-twist light-cone distribution amplitude of the meson M. Power corrections to the decay rates arise first at order (Λ{sub QCD}/m{sub V}){sup 2}. They can be estimated in terms of higher-twist distribution amplitudes and are predicted to be tiny. We include one-loop O(α{sub s}) radiative corrections to the hard-scattering coefficients and perform the resummation of large logarithms (α{sub s}ln (m{sub V}{sup 2}/μ{sub 0}{sup 2})){sup n} (with μ{sub 0}∼1 GeV a typical hadronic scale) to all orders in perturbation theory. Evolution effects have an important impact both numerically and conceptually, since they reduce the sensitivity to poorly determined hadronic parameters. We present detailed numerical predictions and error estimates, which can serve as benchmarks for future precision measurements. We also present an exploratory study of the weak radiative decays Z→MW. Some of the decay modes studied here have branching ratios large enough to be accessible in the high-luminosity run of the LHC. Many of them can be measured with high accuracy at a future lepton collider. This will provide stringent tests of the QCD factorization formalism and enable novel searches for new physics.

  10. QCD and string theories

    International Nuclear Information System (INIS)

    Cohen-Tannoudji, G.

    1990-01-01

    This paper is devoted to a review of the connections between quantumchromodynamics (QCD) and string theories. One reviews the phenomenological models leading to string pictures in non perturbative QCD and the string effects, related to soft gluon coherence, which arise in perturbative QCD. One tries to build a string theory which goes to QCD at the zero slope limit. A specific model, based on superstring theories is shown to agree with QCD four point amplitudes at the Born approximation and with one loop corrections. One shows how this approach can provide a theoretical framework to account for the phenomenological property of parton-hadron duality

  11. QCD and hadronic strings

    International Nuclear Information System (INIS)

    Cohen-Tannoudji, G.

    1989-01-01

    This series of lectures is devoted to review ot he connections between QCD and string theories. One reviews the phenomenological models leading to string pictures in non perturbative QCD and the string effects, related to soft gluon coherence, which arise in perturbative QCD. One tries to build a string theory which goes to QCD at the zero slope limit. A specific model, based on superstring theories is shown to agree with QCD four point amplitudes at the Born approximation and with one loop corrections. One shows how this approach can provide a theoretical framework to account for the phenomenological property of parton-hadron duality.(author)

  12. Efficient evaluation of the Coulomb force in the Gaussian and finite-element Coulomb method.

    Science.gov (United States)

    Kurashige, Yuki; Nakajima, Takahito; Sato, Takeshi; Hirao, Kimihiko

    2010-06-28

    We propose an efficient method for evaluating the Coulomb force in the Gaussian and finite-element Coulomb (GFC) method, which is a linear-scaling approach for evaluating the Coulomb matrix and energy in large molecular systems. The efficient evaluation of the analytical gradient in the GFC is not straightforward as well as the evaluation of the energy because the SCF procedure with the Coulomb matrix does not give a variational solution for the Coulomb energy. Thus, an efficient approximate method is alternatively proposed, in which the Coulomb potential is expanded in the Gaussian and finite-element auxiliary functions as done in the GFC. To minimize the error in the gradient not just in the energy, the derived functions of the original auxiliary functions of the GFC are used additionally for the evaluation of the Coulomb gradient. In fact, the use of the derived functions significantly improves the accuracy of this approach. Although these additional auxiliary functions enlarge the size of the discretized Poisson equation and thereby increase the computational cost, it maintains the near linear scaling as the GFC and does not affects the overall efficiency of the GFC approach.

  13. Light-like Wilson Loops and Cusp Anomalous Dimensions in Nonconformal Gauge Theories

    International Nuclear Information System (INIS)

    Pando Zayas, Leopoldo A.; Phalen, Daniel J.; Terrero-Escalante, Cesar A.

    2008-01-01

    We emphasize that nonconformal theories provide a natural playground for the ideas of the Maldacena conjecture opening the possibility of exploring properties that could potentially be in the same universality class as QCD. In particular, we discuss in detail how light-like Wilson loops, an important ingredient in the prescription for scattering amplitudes, can be described in a number of gravity duals of nonconformal gauge theories. We point out to a few universal properties and the prominent role of the strong scale

  14. Diffusion in Coulomb crystals.

    Science.gov (United States)

    Hughto, J; Schneider, A S; Horowitz, C J; Berry, D K

    2011-07-01

    Diffusion in Coulomb crystals can be important for the structure of neutron star crusts. We determine diffusion constants D from molecular dynamics simulations. We find that D for Coulomb crystals with relatively soft-core 1/r interactions may be larger than D for Lennard-Jones or other solids with harder-core interactions. Diffusion, for simulations of nearly perfect body-centered-cubic lattices, involves the exchange of ions in ringlike configurations. Here ions "hop" in unison without the formation of long lived vacancies. Diffusion, for imperfect crystals, involves the motion of defects. Finally, we find that diffusion, for an amorphous system rapidly quenched from Coulomb parameter Γ=175 to Coulomb parameters up to Γ=1750, is fast enough that the system starts to crystalize during long simulation runs. These results strongly suggest that Coulomb solids in cold white dwarf stars, and the crust of neutron stars, will be crystalline and not amorphous.

  15. Properties of the twisted Polyakov loop coupling and the infrared fixed point in the SU(3) gauge theories

    Science.gov (United States)

    Itou, Etsuko

    2013-08-01

    We report the nonperturbative behavior of the twisted Polyakov loop (TPL) coupling constant for the SU(3) gauge theories defined by the ratio of Polyakov loop correlators in finite volume with twisted boundary condition. We reveal the vacuum structures and the phase structure for the lattice gauge theory with the twisted boundary condition. Carrying out the numerical simulations, we determine the nonperturbative running coupling constant in this renormalization scheme for the quenched QCD and N_f=12 SU(3) gauge theories. First, we study the quenched QCD theory using the plaquette gauge action. The TPL coupling constant has a fake fixed point in the confinement phase. We discuss this fake fixed point of the TPL scheme and obtain the nonperturbative running coupling constant in the deconfinement phase, where the magnitude of the Polyakov loop shows the nonzero values. We also investigate the system coupled to fundamental fermions. Since we use the naive staggered fermion with the twisted boundary condition in our simulation, only multiples of 12 are allowed for the number of flavors. According to the perturbative two-loop analysis, the N_f=12 SU(3) gauge theory might have a conformal fixed point in the infrared region. However, recent lattice studies show controversial results for the existence of the fixed point. We point out possible problems in previous work, and present our careful study. Finally, we find the infrared fixed point (IRFP) and discuss the robustness of the nontrivial IRFP of a many-flavor system under the change of the analysis method. Some preliminary results were reported in the proceedings [E. Bilgici et al., PoS(Lattice 2009), 063 (2009); Itou et al., PoS(Lattice 2010), 054 (2010)] and the letter paper [T. Aoyama et al., arXiv:1109.5806 [hep-lat

  16. A Simultaneous Measurement of the QCD Colour Factors and the Strong Coupling

    CERN Document Server

    Abbiendi, G.; Akesson, P.F.; Alexander, G.; Allison, John; Anagnostou, G.; Anderson, K.J.; Arcelli, S.; Asai, S.; Axen, D.; Azuelos, G.; Bailey, I.; Ball, H.; Barberio, E.; Barlow, Roger J.; Batley, R.J.; Behnke, T.; Bell, Kenneth Watson; Bella, G.; Bellerive, A.; Benelli, G.; Bethke, S.; Biebel, O.; Bloodworth, I.J.; Boeriu, O.; Bock, P.; Bohme, J.; Bonacorsi, D.; Boutemeur, M.; Braibant, S.; Brigliadori, L.; Brown, Robert M.; Burckhart, H.J.; Cammin, J.; Capiluppi, P.; Carnegie, R.K.; Caron, B.; Carter, A.A.; Carter, J.R.; Chang, C.Y.; Charlton, David G.; Clarke, P.E.L.; Clay, E.; Cohen, I.; Couchman, J.; Csilling, A.; Cuffiani, M.; Dado, S.; Dallavalle, G.Marco; Dallison, S.; De Roeck, A.; De Wolf, E.A.; Dervan, P.; Desch, K.; Dienes, B.; Dixit, M.S.; Donkers, M.; Dubbert, J.; Duchovni, E.; Duckeck, G.; Duerdoth, I.P.; Estabrooks, P.G.; Etzion, E.; Fabbri, F.; Fanti, M.; Feld, L.; Ferrari, P.; Fiedler, F.; Fleck, I.; Ford, M.; Frey, A.; Furtjes, A.; Futyan, D.I.; Gagnon, P.; Gary, J.W.; Gaycken, G.; Geich-Gimbel, C.; Giacomelli, G.; Giacomelli, P.; Glenzinski, D.; Goldberg, J.; Grandi, C.; Graham, K.; Gross, E.; Grunhaus, J.; Gruwe, M.; Gunther, P.O.; Gupta, A.; Hajdu, C.; Hanson, G.G.; Harder, K.; Harel, A.; Harin-Dirac, M.; Hauschild, M.; Hawkes, C.M.; Hawkings, R.; Hemingway, R.J.; Hensel, C.; Herten, G.; Heuer, R.D.; Hill, J.C.; Hoffman, Kara Dion; Homer, R.J.; Honma, A.K.; Horvath, D.; Hossain, K.R.; Howard, R.; Huntemeyer, P.; Igo-Kemenes, P.; Ishii, K.; Jawahery, A.; Jeremie, H.; Jones, C.R.; Jovanovic, P.; Junk, T.R.; Kanaya, N.; Kanzaki, J.; Karapetian, G.; Karlen, D.; Kartvelishvili, V.; Kawagoe, K.; Kawamoto, T.; Keeler, R.K.; Kellogg, R.G.; Kennedy, B.W.; Kim, D.H.; Klein, K.; Klier, A.; Kluth, S.; Kobayashi, T.; Kobel, M.; Kokott, T.P.; Komamiya, S.; Kowalewski, Robert V.; Kamer, T.; Kress, T.; Krieger, P.; von Krogh, J.; Krop, D.; Kuhl, T.; Kupper, M.; Kyberd, P.; Lafferty, G.D.; Landsman, H.; Lanske, D.; Lawson, I.; Layter, J.G.; Leins, A.; Lellouch, D.; Letts, J.; Levinson, L.; Liebisch, R.; Lillich, J.; Littlewood, C.; Lloyd, A.W.; Lloyd, S.L.; Loebinger, F.K.; Long, G.D.; Losty, M.J.; Lu, J.; Ludwig, J.; Macchiolo, A.; Macpherson, A.; Mader, W.; Marcellini, S.; Marchant, T.E.; Martin, A.J.; Martin, J.P.; Martinez, G.; Mashimo, T.; Mattig, Peter; McDonald, W.John; McKenna, J.; McMahon, T.J.; McPherson, R.A.; Meijers, F.; Mendez-Lorenzo, P.; Menges, W.; Merritt, F.S.; Mes, H.; Michelini, A.; Mihara, S.; Mikenberg, G.; Miller, D.J.; Mohr, W.; Montanari, A.; Mori, T.; Nagai, K.; Nakamura, I.; Neal, H.A.; Nisius, R.; O'Neale, S.W.; Oakham, F.G.; Odorici, F.; Oh, A.; Okpara, A.; Oreglia, M.J.; Orito, S.; Pahl, C.; Pasztor, G.; Pater, J.R.; Patrick, G.N.; Pilcher, J.E.; Pinfold, J.; Plane, David E.; Poli, B.; Polok, J.; Pooth, O.; Quadt, A.; Rabbertz, K.; Rembser, C.; Renkel, P.; Rick, H.; Rodning, N.; Roney, J.M.; Rosati, S.; Roscoe, K.; Rossi, A.M.; Rozen, Y.; Runge, K.; Runolfsson, O.; Rust, D.R.; Sachs, K.; Saeki, T.; Sahr, O.; Sarkisian, E.K.G.; Sbarra, C.; Schaile, A.D.; Schaile, O.; Scharff-Hansen, P.; Schroder, Matthias; Schumacher, M.; Schwick, C.; Scott, W.G.; Seuster, R.; Shears, T.G.; Shen, B.C.; Shepherd-Themistocleous, C.H.; Sherwood, P.; Siroli, G.P.; Skuja, A.; Smith, A.M.; Snow, G.A.; Sobie, R.; Soldner-Rembold, S.; Spagnolo, S.; Spano, F.; Sproston, M.; Stahl, A.; Stephens, K.; Strom, David M.; Strohmer, R.; Stumpf, L.; Surrow, B.; Talbot, S.D.; Tarem, S.; Tasevsky, M.; Taylor, R.J.; Teuscher, R.; Thomas, J.; Thomson, M.A.; Torrence, E.; Towers, S.; Toya, D.; Trefzger, T.; Trigger, I.; Trocsanyi, Z.; Tsur, E.; Turner-Watson, M.F.; Ueda, I.; Vachon, B.; Vollmer, C.F.; Vannerem, P.; Verzocchi, M.; Voss, H.; Vossebeld, J.; Waller, D.; Ward, C.P.; Ward, D.R.; Watkins, P.M.; Watson, A.T.; Watson, N.K.; Wells, P.S.; Wengler, T.; Wermes, N.; Wetterling, D.; White, J.S.; Wilson, G.W.; Wilson, J.A.; Wyatt, T.R.; Yamashita, S.; Zacek, V.; Zer-Zion, D.

    2001-01-01

    Using data from e+e- annihilation into hadrons, taken with the OPAL detector at LEP at the Z pole between 1991 and 1995, we performed a simultaneous measurement of the colour factors of the underlying gauge group of the strong interaction, CF and CA, and the strong coupling, alpha(s). The measurement was carried out by fitting next-to-leading order perturbative predictions to measured angular correlations of 4-jet events together with multi-jet related variables. Our results, CA = 3.02 +/- 0.25 (stat.) +/- 0.49 (syst.) CF = 1.34 +/- 0.13 (stat.) +/- 0.22 (syst.), alpha(s)(M_Z) = 0.120 +/- 0.011 (stat.) +/- 0.020 (syst.), provide a test of perturbative QCD in which the only assumptions are non-abelian gauge symmetry and standard hadronization models. The measurements are in agreement with SU(3) expectations for CF and CA and the world average of alpha(s)(M_Z).

  17. NLO QCD corrections to tt-barbb-bar production at the LHC: 1. quark-antiquark annihilation

    International Nuclear Information System (INIS)

    Bredenstein, A.; Denner, A.; Dittmaier, S.; Pozzorini, S.

    2008-01-01

    The process pp → tt-barbb-bar + X represents a very important background reaction to searches at the LHC, in particular to tt-barH production where the Higgs boson decays into a bb-bar pair. A successful analysis of tt-barH at the LHC requires the knowledge of direct tt-barbb-bar production at next-to-leading order in QCD. We take the first step in this direction upon calculating the next-to-leading-order QCD corrections to the subprocess initiated by q q-bar annihilation. We devote an appendix to the general issue of rational terms resulting from ultraviolet or infrared (soft or collinear) singularities within dimensional regularization. There we show that, for arbitrary processes, in the Feynman gauge, rational terms of infrared origin cancel in truncated one-loop diagrams and result only from trivial self-energy corrections.

  18. Deconfinement, chiral transition and localisation in a QCD-like model

    Energy Technology Data Exchange (ETDEWEB)

    Giordano, Matteo; Katz, Sándor D. [Institute for Theoretical Physics, Eötvös University,Pázmány P. sétány 1/A, H-1117 Budapest (Hungary); MTA-ELTE “Lendület” Lattice Gauge Theory Research Group,Pázmány P. sétány 1/A, H-1117 Budapest (Hungary); Kovács, Tamás G. [Institute for Nuclear Research of the Hungarian Academy of Sciences,Bem tér 18/c, H-4026 Debrecen (Hungary); Pittler, Ferenc [HISKP(Theory), University of Bonn,Nussallee 14-16, D-53115 Bonn (Germany)

    2017-02-10

    We study the problems of deconfinement, chiral symmetry restoration and localisation of the low Dirac eigenmodes in a toy model of QCD, namely unimproved staggered fermions on lattices of temporal extension N{sub T}=4. This model displays a genuine deconfining and chirally-restoring first-order phase transition at some critical value of the gauge coupling. Our results indicate that the onset of localisation of the lowest Dirac eigenmodes takes place at the same critical coupling where the system undergoes the first-order phase transition. This provides further evidence of the close relation between deconfinement, chiral symmetry restoration and localisation of the low modes of the Dirac operator on the lattice.

  19. Instanton dominance over αs at low momenta from lattice QCD simulations at Nf = 0, Nf = 2 + 1 and Nf = 2 + 1 + 1

    Science.gov (United States)

    Athenodorou, Andreas; Boucaud, Philippe; de Soto, Feliciano; Rodríguez-Quintero, José; Zafeiropoulos, Savvas

    2018-03-01

    We report on an instanton-based analysis of the gluon Green functions in the Landau gauge for low momenta; in particular we use lattice results for αs in the symmetric momentum subtraction scheme (MOM) for large-volume lattice simulations. We have exploited quenched gauge field configurations, Nf = 0, with both Wilson and tree-level Symanzik improved actions, and unquenched ones with Nf = 2 + 1 and Nf = 2 + 1 + 1 dynamical flavors (domain wall and twisted-mass fermions, respectively). We show that the dominance of instanton correlations on the low-momenta gluon Green functions can be applied to the determination of phenomenological parameters of the instanton liquid and, eventually, to a determination of the lattice spacing. We furthermore apply the Gradient Flow to remove short-distance fluctuations. The Gradient Flow gets rid of the QCD scale, ΛQCD, and reveals that the instanton prediction extents to large momenta. For those gauge field configurations free of quantum fluctuations, the direct study of topological charge density shows the appearance of large-scale lumps that can be identified as instantons, giving access to a direct study of the instanton density and size distribution that is compatible with those extracted from the analysis of the Green functions.

  20. Non-Perturbative QCD Coupling and Beta Function from Light Front Holography

    Energy Technology Data Exchange (ETDEWEB)

    Brodsky, Stanley J.; /SLAC /Southern Denmark U., CP3-Origins; de Teramond, Guy F.; /Costa Rica U.; Deur, Alexandre; /Jefferson Lab

    2010-05-26

    The light-front holographic mapping of classical gravity in AdS space, modified by a positive-sign dilaton background, leads to a non-perturbative effective coupling {alpha}{sub s}{sup AdS} (Q{sup 2}). It agrees with hadron physics data extracted from different observables, such as the effective charge defined by the Bjorken sum rule, as well as with the predictions of models with built-in confinement and lattice simulations. It also displays a transition from perturbative to nonperturbative conformal regimes at a momentum scale {approx} 1 GeV. The resulting {beta}-function appears to capture the essential characteristics of the full {beta}-function of QCD, thus giving further support to the application of the gauge/gravity duality to the confining dynamics of strongly coupled QCD. Commensurate scale relations relate observables to each other without scheme or scale ambiguity. In this paper we extrapolate these relations to the nonperturbative domain, thus extending the range of predictions based on {alpha}{sub s}{sup AdS} (Q{sup 2}).

  1. Improved actions for QCD thermodynamics on the lattice

    CERN Document Server

    Beinlich, B; Laermann, E

    1996-01-01

    Finite cut-off effects strongly influence the thermodynamics of lattice regularized QCD at high temperature in the standard Wilson formulation. We analyze the reduction of finite cut-off effects in formulations of the thermodynamics of SU(N) gauge theories with three different O(a^2) and O(a^4) improved actions. We calculate the energy density and pressure on finite lattices in leading order weak coupling perturbation theory (T\\rightarrow \\infty) and perform Monte Carlo simulations with improved SU(3) actions at non-zero g^2. Already on lattices with temporal extent N_\\tau=4 we find a strong reduction of finite cut-off effects in the high temperature limit, which persists also down to temperatures a few times the deconfinement transition temperature.

  2. A possible description of baryon dynamics in dual and gauge theories

    CERN Document Server

    Rossi, G C

    1977-01-01

    The authors generalize to baryons a framework recently proposed in order to unify gauge, dual and Regge-Gribov theories of mesons. They depart from the 1/N/sub colour/ expansion of quantum chromodynamics (QCD) and replace it by a more general definition of a 'dual' approximation of QCD, based on the zero-width limit. Theoretical and phenomenological consequences of the scheme are derived. For N/sub colour/=3, the baryon resembles a Y shaped string; three families of new 'baryonium' bound states are predicted and rough estimates of intercepts and slopes of the associated Regge trajectories are given. A new type of Zweig-like selection rule is found to hold in leading order and its violations through higher-order topologies are discussed. Duality diagrams for baryons are ambiguous unless implemented with extra lines indicating the flow of certain colour indices. Duality between scattering and annihilation channels is found in BB scattering and its consequences are discussed. Some justification is given for the ...

  3. On-shell gauge-parameter independence of contributions to electroweak quark self-energies

    International Nuclear Information System (INIS)

    Ahmady, M.R.; Elias, V.; Mendel, R.R.; Scadron, M.D.; Steele, T.

    1989-01-01

    We allow an external condensate to enter standard SU(2) x U(1) electroweak theory via the vacuum expectation value , as in QCD sum-rule applications. For a given flavor, we then find that any gauge-parameter dependence of quark self-energies on the ''mass shell'' is eliminated provided that the mass shell is made to coincide with both the expansion-parameter mass occurring in the operator-product expansion of and the standard electroweak mass acquired via the Yukawa coupling to the usual scalar vacuum expectation value of spontaneous symmetry breaking. This result indicates that if the QCD-generated order parameter and associated dynamical mass(es) m/sub q//sup dyn/ are utilized as external input parameters in electroweak calculations involving hadrons, then new corrections must be introduced into the q-barqW and q-barqZ vertices in order to preserve SU(2) x U(1) Ward identities

  4. Hyperspherical Coulomb spheroidal basis in the Coulomb three-body problem

    International Nuclear Information System (INIS)

    Abramov, D. I.

    2013-01-01

    A hyperspherical Coulomb spheroidal (HSCS) representation is proposed for the Coulomb three-body problem. This is a new expansion in the set of well-known Coulomb spheroidal functions. The orthogonality of Coulomb spheroidal functions on a constant-hyperradius surface ρ = const rather than on a constant-internuclear-distance surface R = const, as in the traditional Born-Oppenheimer approach, is a distinguishing feature of the proposed approach. Owing to this, the HSCS representation proves to be consistent with the asymptotic conditions for the scattering problem at energies below the threshold for three-body breakup: only a finite number of radial functions do not vanish in the limit of ρ→∞, with the result that the formulation of the scattering problem becomes substantially simpler. In the proposed approach, the HSCS basis functions are considerably simpler than those in the well-known adiabatic hyperspherical representation, which is also consistent with the asymptotic conditions. Specifically, the HSCS basis functions are completely factorized. Therefore, there arise no problems associated with avoided crossings of adiabatic hyperspherical terms.

  5. Introduction to gauge theories of the strong, weak, and electromagnetic interactions

    International Nuclear Information System (INIS)

    Quigg, C.

    1980-07-01

    The plan of these notes is as follows. Chapter 1 is devoted to a brief evocative review of current beliefs and prejudices that form the context for the discussion to follow. The idea of Gauge Invariance is introduced in Chapter 2, and the connection between conservation laws and symmetries of the Lagrangian is recalled. Non-Abelian gauge field theories are constructed in Chapter 3, by analogy with the familiar case of electromagnetism. The Yang-Mills theory based upon isospin symmetry is constructed explicitly, and the generalization is made to other gauge groups. Chapter 4 is concerned with spontaneous symmetry breaking and the phenomena that occur in the presence or absence of local gauge symmetries. The existence of massless scalar fields (Goldstone particles) and their metamorphosis by means of the Higgs mechanism are illustrated by simple examples. The Weinberg-Salam model is presented in Chapter 5, and a brief resume of applications to experiment is given. Quantum Chromodynamics, the gauge theory of colored quarks and gluons, is developed in Chapter 6. Asymptotic freedom is derived schematically, and a few simple applications of perturbative QCD ae exhibited. Details of the conjectured confinement mechanism are omitted. The strategy of grand unified theories of the strong, weak, and electromagnetic interactions is laid out in Chapter 7. Some properties and consequences of the minimal unifying group SU(5) are presented, and the gauge hierarchy problem is introduced in passing. The final chapter contains an essay on the current outlook: aspirations, unanswered questions, and bold scenarios

  6. Reducing cutoff effects in maximally twisted lattice QCD close to the chiral limit

    International Nuclear Information System (INIS)

    Frezzotti, R.; Papinutto, M.; Rossi, G.C.; Istituto Nazionale di Fisica Nucleare, Rome; Deutsches Elektronen-Synchrotron

    2005-03-01

    When analyzed in terms of the Symanzik expansion, the expectation values of multi-local (gauge-invariant) operators with non-trivial continuum limit exhibit in maximally twisted lattice QCD ''infrared divergent'' cutoff effects of the type a 2k /(m π 2 ) h , 2k ≥ h ≥ 1, which become numerically dangerous when the pion mass gets small. We prove that, if the critical mass counter-term is chosen in some ''optimal'' way or, alternatively, the action is O(a) improved a la Symanzik, the leading cutoff effects of this kind (i.e. those with h = 2k) can all be eliminated. Once this is done, the remaining next-to-leading ''infrared divergent'' effects are only of the kind a 2 (a 2 /m π 2 ) k , k ≥ 1. This implies that the continuum extrapolation of lattice results is smooth at least down to values of the quark mass, m q , satisfying the order of magnitude inequality m q > a 2 Λ QCD 3 . (orig.)

  7. The Λ-parameter in 3-flavour QCD and α{sub s}(m{sub Z}) by the Alpha collaboration

    Energy Technology Data Exchange (ETDEWEB)

    Bruno, M. [Brookhaven National Laboratory, Upton, NY (United States). Physics Dept.; Dalla Brida, Mattia [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC; Milano-Bicocca Univ. (Italy). Dipt. di Fisica; INFN, Milano-Bicocca (Italy); Fritzsch, P. [CERN, Geneva (Switzerland). PH-TH; Univ. Autonoma de Madrid (Spain). Inst. de Fisica Teorica; Korzec, T. [Wuppertal Univ. (Germany). Dept. of Physics; Ramos, Alberto [CERN, Geneva (Switzerland). PH-TH; Schaefer, Stefan; Simma, Hubert [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC; Sint, S. [Trinity Coll., Dublin (Ireland). School of Mathematics and Hamilton Mathematics Inst.; Sommer, R. [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC; Humboldt-Universitaet, Berlin (Germany). Inst. fuer Physik; Collaboration: ALPHA Collaboration

    2017-01-15

    We present results by the ALPHA collaboration for the Λ-parameter in 3-flavour QCD and the strong coupling constant at the electroweak scale, α{sub s}(m{sub Z}), in terms of hadronic quantities computed on the CLS gauge configurations. The first part of this proceedings contribution contains a review of published material and yields the Λ-parameter in units of a low energy scale, 1/L{sub had}. We then discuss how to determine this scale in physical units from experimental data for the pion and kaon decay constants. We obtain Λ{sup (3)}{sub MS}=332(14) MeV which translates to α{sub s}(M{sub Z})=0.1179(10)(2) using perturbation theory to match between 3-, 4- and 5-flavour QCD.

  8. Integral equation for Coulomb problem

    International Nuclear Information System (INIS)

    Sasakawa, T.

    1986-01-01

    For short range potentials an inhomogeneous (homogeneous) Lippmann-Schwinger integral equation of the Fredholm type yields the wave function of scattering (bound) state. For the Coulomb potential, this statement is no more valid. It has been felt difficult to express the Coulomb wave function in a form of an integral equation with the Coulomb potential as the perturbation. In the present paper, the author shows that an inhomogeneous integral equation of a Volterra type with the Coulomb potential as the perturbation can be constructed both for the scattering and the bound states. The equation yielding the binding energy is given in an integral form. The present treatment is easily extended to the coupled Coulomb problems

  9. Holographic repulsion and confinement in gauge theory

    Science.gov (United States)

    Husain, Viqar; Kothawala, Dawood

    2013-02-01

    We show that for asymptotically anti-de Sitter (AdS) backgrounds with negative energy, such as the AdS soliton and regulated negative-mass AdS-Schwarzshild metrics, the Wilson loop expectation value in the AdS/CFT conjecture exhibits a Coulomb to confinement transition. We also show that the quark-antiquark (q \\bar{q}) potential can be interpreted as affine time along null geodesics on the minimal string worldsheet and that its intrinsic curvature provides a signature of transition to confinement phase. Our results suggest a generic (holographic) relationship between confinement in gauge theory and repulsive gravity, which in turn is connected with singularity avoidance in quantum gravity. Communicated by P R L V Moniz

  10. DESY: QCD workshop

    International Nuclear Information System (INIS)

    Ingelman, Gunnar

    1994-01-01

    The traditional annual DESY Theory Workshop highlights a topical theory sector. The most recent was under the motto 'Quantum Chromo-Dynamics' - QCD, the field theory of quarks and gluons. The organizers had arranged a programme covering most aspects of current QCD research. This time the workshop was followed by a topical meeting on 'QCD at HERA' to look at the electron-proton scattering experiments now in operation at DESY's new HERA collider

  11. The static quark potential from the gauge independent Abelian decomposition

    Energy Technology Data Exchange (ETDEWEB)

    Cundy, Nigel, E-mail: ndcundy@gmail.com [Lattice Gauge Theory Research Center, FPRD, and CTP, Department of Physics & Astronomy, Seoul National University, Seoul 151-747 (Korea, Republic of); Cho, Y.M. [Administration Building 310-4, Konkuk University, Seoul 143-701 (Korea, Republic of); Department of Physics & Astronomy, Seoul National University, Seoul 151-747 (Korea, Republic of); Lee, Weonjong; Leem, Jaehoon [Lattice Gauge Theory Research Center, FPRD, and CTP, Department of Physics & Astronomy, Seoul National University, Seoul 151-747 (Korea, Republic of)

    2015-06-15

    We investigate the relationship between colour confinement and the gauge independent Cho–Duan–Ge Abelian decomposition. The decomposition is defined in terms of a colour field n; the principle novelty of our study is that we have used a unique definition of this field in terms of the eigenvectors of the Wilson Loop. This allows us to establish an equivalence between the path-ordered integral of the non-Abelian gauge fields and an integral over an Abelian restricted gauge field which is tractable both theoretically and numerically in lattice QCD. We circumvent path ordering without requiring an additional path integral. By using Stokes' theorem, we can compute the Wilson Loop in terms of a surface integral over a restricted field strength, and show that the restricted field strength may be dominated by certain structures, which occur when one of the quantities parametrising the colour field n winds itself around a non-analyticity in the colour field. If they exist, these structures will lead to an area law scaling for the Wilson Loop and provide a mechanism for quark confinement. Unlike most studies of confinement using the Abelian decomposition, we do not rely on a dual-Meissner effect to create the inter-quark potential. We search for these structures in quenched lattice QCD. We perform the Abelian decomposition, and compare the electric and magnetic fields with the patterns expected theoretically. We find that the restricted field strength is dominated by objects which may be peaks of a single lattice spacing in size or extended string-like lines of electromagnetic flux. The objects are not isolated monopoles, as they generate electric fields in addition to magnetic fields, and the fields are not spherically symmetric, but may be either caused by a monopole/anti-monopole condensate, some other types of topological objects, or a combination of these. Removing these peaks removes the area law scaling of the string tension, suggesting that they are

  12. The static quark potential from the gauge independent Abelian decomposition

    Directory of Open Access Journals (Sweden)

    Nigel Cundy

    2015-06-01

    Full Text Available We investigate the relationship between colour confinement and the gauge independent Cho–Duan–Ge Abelian decomposition. The decomposition is defined in terms of a colour field n; the principle novelty of our study is that we have used a unique definition of this field in terms of the eigenvectors of the Wilson Loop. This allows us to establish an equivalence between the path-ordered integral of the non-Abelian gauge fields and an integral over an Abelian restricted gauge field which is tractable both theoretically and numerically in lattice QCD. We circumvent path ordering without requiring an additional path integral. By using Stokes' theorem, we can compute the Wilson Loop in terms of a surface integral over a restricted field strength, and show that the restricted field strength may be dominated by certain structures, which occur when one of the quantities parametrising the colour field n winds itself around a non-analyticity in the colour field. If they exist, these structures will lead to an area law scaling for the Wilson Loop and provide a mechanism for quark confinement. Unlike most studies of confinement using the Abelian decomposition, we do not rely on a dual-Meissner effect to create the inter-quark potential.We search for these structures in quenched lattice QCD. We perform the Abelian decomposition, and compare the electric and magnetic fields with the patterns expected theoretically. We find that the restricted field strength is dominated by objects which may be peaks of a single lattice spacing in size or extended string-like lines of electromagnetic flux. The objects are not isolated monopoles, as they generate electric fields in addition to magnetic fields, and the fields are not spherically symmetric, but may be either caused by a monopole/anti-monopole condensate, some other types of topological objects, or a combination of these. Removing these peaks removes the area law scaling of the string tension, suggesting that

  13. The static quark potential from the gauge independent Abelian decomposition

    Science.gov (United States)

    Cundy, Nigel; Cho, Y. M.; Lee, Weonjong; Leem, Jaehoon

    2015-06-01

    We investigate the relationship between colour confinement and the gauge independent Cho-Duan-Ge Abelian decomposition. The decomposition is defined in terms of a colour field n; the principle novelty of our study is that we have used a unique definition of this field in terms of the eigenvectors of the Wilson Loop. This allows us to establish an equivalence between the path-ordered integral of the non-Abelian gauge fields and an integral over an Abelian restricted gauge field which is tractable both theoretically and numerically in lattice QCD. We circumvent path ordering without requiring an additional path integral. By using Stokes' theorem, we can compute the Wilson Loop in terms of a surface integral over a restricted field strength, and show that the restricted field strength may be dominated by certain structures, which occur when one of the quantities parametrising the colour field n winds itself around a non-analyticity in the colour field. If they exist, these structures will lead to an area law scaling for the Wilson Loop and provide a mechanism for quark confinement. Unlike most studies of confinement using the Abelian decomposition, we do not rely on a dual-Meissner effect to create the inter-quark potential. We search for these structures in quenched lattice QCD. We perform the Abelian decomposition, and compare the electric and magnetic fields with the patterns expected theoretically. We find that the restricted field strength is dominated by objects which may be peaks of a single lattice spacing in size or extended string-like lines of electromagnetic flux. The objects are not isolated monopoles, as they generate electric fields in addition to magnetic fields, and the fields are not spherically symmetric, but may be either caused by a monopole/anti-monopole condensate, some other types of topological objects, or a combination of these. Removing these peaks removes the area law scaling of the string tension, suggesting that they are responsible for

  14. Phases of QCD

    International Nuclear Information System (INIS)

    Roessner, Simon

    2009-01-01

    Quantum Chromodynamics (QCD) is the theory of the strong interaction within the Standard Model of elementary particles. Today's research in this area dedicates substantial resources to numeric solutions of the QCD field equations and experimental programs exploring the phases of QCD. This thesis proceeds along a complementary line - that of modelling QCD, with the aim of identifying its dominant degrees of freedom. This is possible by minimally coupling effective potentials for the Polyakov loop to Nambu-Jona-Lasinio models using temporal background fields to model chiral symmetry breaking respecting colour confinement. The fermion sign problem resulting from the minimal coupling is addressed in this work establishing a novel, systematically ordered approach. The modifications to the approximative order parameter of colour confinement, the Polyakov loop, are in direct connection with the fermion sign problem. Furthermore an effective coupling of quark densities of different flavours is induced. This mechanism, most likely also present in QCD, produces finite contributions to flavour off diagonal susceptibilities. Susceptibilities are amongst the most promising physical quantities for the experimental exploration of the phase transition at high temperatures and densities. (orig.)

  15. QCD phenomenology

    International Nuclear Information System (INIS)

    Gaillard, M.K.

    1979-01-01

    Selected topics in QCD phenomenology are reviewed: the development of an effective jet perturbation series with applications to factorization, energy flow analysis and photon physics; implications of non-perturbative phenomena for hard scattering processes and the pseudoscalar mass spectrum; resonance properties as extracted from the combined technologies of perturbative and non-perturbative QCD. (orig.)

  16. [Investigations in dynamics of gauge theories in theoretical particle physics

    International Nuclear Information System (INIS)

    1993-01-01

    The major theme of the theoretical physics research conducted under DOE support over the past several years has been within the rubric of the standard model, and concerned the interplay between symmetries and dynamics. The research was thus carried out mostly in the context of gauge field theories, and usually in the presence of chiral fermions. Dynamical symmetry breaking was examined both from the point of view of perturbation theory, as well as from non-perturbative techniques associated with certain characteristic features of specific theories. Among the topics of research were: the implications of abelian and non-abelian anomalies on the spectrum and possible dynamical symmetry breaking in any theory, topological and conformal properties of quantum fields in two and higher dimensions, the breaking of global chiral symmetries by vector-like gauge theories such as QCD, the phenomenological implications of a strongly interacting Higgs sector in the standard model, and the application of soliton ideas to the physics to be explored at the SSC

  17. Expansions for Coulomb wave functions

    NARCIS (Netherlands)

    Boersma, J.

    1969-01-01

    In this paper we derive a number of expansions for Whittaker functions, regular and irregular Coulomb wave functions. The main result consists of a new expansion for the irregular Coulomb wave functions of orders zero and one in terms of regular Coulomb wave functions. The latter expansions are

  18. Standard model group, QCD subgroup - dynamics isolating and testing the elementary QCD subprocess

    International Nuclear Information System (INIS)

    Tannenbaum, M.J.

    1982-01-01

    QCD to an experimentalist is the theory of interactions of quarks and gluons. Experimentalists like QCD because QCD is analogous to QED. Thus, following Drell and others who have for many years studied the validity of QED, one has a ready-made menu for tests of QCD. There are the static and long distance tests. These topics are covered by Peter LePage in the static properties group. In this report, dynamic and short distance tests of QCD will be discussed, primarily via reactions with large transverse momenta. This report is an introduction and overview of the subject, to serve as a framework for other reports from the subgroup. In the last two sections, the author has taken the opportunity to discuss his own ideas and opinions

  19. Chiral symmetry breaking and nonperturbative scale anomaly in gauge field theories

    International Nuclear Information System (INIS)

    Miranskij, V.A.; Gusynin, V.P.

    1987-01-01

    The nonperturbative dynamics of chiral and scale symmetry breaking in asymtotically free and non-asymptotically free (with an ultraviolet stable fixed point) vector-like gauge theories is investigated. In the two-loop approximation analytical expressions for the chiral and gluon condensates are obtained. The hypothesis about a soft behaviour at small distances of composite operators in non-asymptotically free gauge theories with a fixed point is put forward and substantiated. It is shown that in these theories the form of the scale anomaly depends on the type of the phase in coupling constant to which it relates. A new dilaton effective lagrangian for glueball and chiral fields is suggested. The mass relation for the single scalar fermion-antifermion bound state is obtained. The important ingredient of this approach is a large (d≅ 2) dynamical dimension of composite chiral fields. The application of this approach to QCD and technicolour models is discussed

  20. Exceptional thermodynamics. The equation of state of G{sub 2} gauge theory

    Energy Technology Data Exchange (ETDEWEB)

    Bruno, Mattia [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC; Caselle, Michele [Torino Univ. (Italy). Dipt. di Fisica Teorica; INFN, Sezione di Torino (Italy); Panero, Marco [Univ. Autonoma de Madrid (Spain). Inst. de Fisica Teorica; Consejo Superior de Investigaciones Cientificas, Madrid (Spain); Pellegrini, Roberto [Swansea Univ. (United Kingdom). Dept. of Physics

    2014-10-15

    We present a lattice study of the equation of state in Yang-Mills theory based on the exceptional G{sub 2} gauge group. As is well-known, at zero temperature this theory shares many qualitative features with real-world QCD, including the absence of colored states in the spectrum and dynamical string breaking at large distances. In agreement with previous works, we show that at finite temperature this theory features a first-order deconfining phase transition, whose nature can be studied by a semi-classical computation. We also show that the equilibrium thermodynamic observables in the deconfined phase bear striking quantitative similarities with those found in SU(N) gauge theories: in particular, these quantities exhibit nearly perfect proportionality to the number of gluon degrees of freedom, and the trace anomaly reveals a characteristic quadratic dependence on the temperature, also observed in SU(N) Yang-Mills theories (both in four and in three spacetime dimensions). We compare our lattice data with analytical predictions from effective models, and discuss their implications for the deconfinement mechanism and high-temperature properties of strongly interacting, non-supersymmetric gauge theories. Our results give strong evidence for the conjecture that the thermal deconfining transition is governed by a universal mechanism, common to all simple gauge groups.