|
|
|
Lepton Flavour Violation in Models with A4 Flavour Symmetry
2009-01-01
I discuss lepton flavour violating transitions, leptonic magnetic dipole moments (MDMs) and electric dipole moments (EDMs) in a class of models characterized by the flavour symmetry A4 x Z3 x U(1)FN. I present the relevant low-energy effective Lagrangian where these effects are dominated by dimension six operators, suppressed by the scale M of new physics. All the flavour breaking effects are universally described by the vacuum expectation values of a set of spurions. I separately analyze both a supersymmetric and a general case. While the observed discrepancy delta amu in the anomalous MDM of the muon suggests M of order of a few TeV, several data require M above 10 TeV, in particular the limit on EDM of the electron. In the general case also the present limit on BR(mu -> e gamma) requires M >10 ... >>
Lepton Flavour Violation in Models with A4 Flavour Symmetry
2009-01-01
The approximated tri-bimaximal mixing (TBM) observed in the n oscillations is a particular feature of a class of models characterized by the spontaneously broken horizontal flavour symmetry Formula Not Shown . In this paper, it is presented an analysis on the predictions of these models for relevant low-energy observables. In an effective operator approach, these effects are dominated by dim-6 operators, suppressed by the scale M of new physics (NP). Indications for M and an upper bound on Formula Not Shown of a few percent are found.
Lepton Flavour Violation in Models with A4 Flavour Symmetry
2008-07-22
We analyze lepton flavour violating transitions, leptonic magnetic dipole moments (MDMs) and electric dipole moments (EDMs) in a class of models characterized by the flavour symmetry A4 x Z3 x U(1)_{FN}, whose choice is motivated by the approximate tri-bimaximal mixing observed in neutrino oscillations. We construct the relevant low-energy effective Lagrangian where these effects are dominated by dimension six operators, suppressed by the scale M of new physics. All the flavour breaking effects are universally described by the vacuum expectation values of a set of spurions. We separately analyze both a supersymmetric and a general case. While the observed discrepancy delta a_mu in the anomalous MDM of the muon suggests M of order of a few TeV, several data require M above 10 TeV, in particular the limit on EDM of the electron. In the general case also the present limit on BR(mu -> e gamma) requires M >10 TeV, at least. The branching ratios for mu -> e gamma, tau -> mu gamma and tau -> e gamma are all expected to be of the same order. In the supersymmetric case the constraint from mu -> e gamma is softened and it can be satisfied by a smaller scale M. In this case both the observed delta a_mu and the current bound on BR(mu -> e gamma) can be satisfied, at the price of a rather small value for ||, of the order of a few percents, that reflects on a similar value for theta_{13}.
Lepton Flavour Violation in a Supersymmetric Model with A4 Flavour Symmetry
2009-11-20
We compute the branching ratios for mu-> e gamma, tau-> mu gamma and tau -> e gamma in a supersymmetric model invariant under the flavour symmetry group A4 X Z3 X U(1)_{FN}, in which near tri-bimaximal lepton mixing is naturally predicted. At leading order in the small symmetry breaking parameter u, which is of the same order as the reactor mixing angle theta_{13}, we find that the branching ratios generically scale as u^2. Applying the current bound on the branching ratio of mu -> e gamma shows that small values of u or tan(beta) are preferred in the model for mass parameters m_{SUSY} and m_{1/2} smaller than 1000 GeV. The bound expected from the on-going MEG experiment will provide a severe constraint on the parameter space of the model either enforcing u approx 0.01 and small tan(beta) or m_{SUSY} and m_{1/2} above 1000 GeV. In the special case of universal soft supersymmetry breaking terms in the flavon sector a cancellation takes place in the amplitudes and the branching ratios scale as u^4, allowing for smaller slepton masses. The branching ratios for tau -> mu gamma and tau -> e gamma are predicted to be of the same order as the one for mu -> e gamma, which precludes the possibility of observing these tau decays in the near future.
LFV in Models with A4 Flavour Symmetry
2008-11-24
The approximated tri-bimaximal mixing observed in the neutrino oscillations is a particular feature of a class of models characterized by the spontaneously broken horizontal flavour symmetry A4. In this paper, it is presented an analysis on the predictions of these models for relevant low-energy observables. In an effective operator approach, these effects are dominated by dim-6 operators, suppressed by the scale M of new physics. Indications for M and an upper bound on \theta_{13} of a few percent are found.
LFV and Dipole Moments in Models with A4 Flavour Symmetry
2009-02-19
It is presented an analysis on lepton flavour violating transitions, leptonic magnetic dipole moments and electric dipole moments in a class of models characterized by the flavour symmetry A4 x Z3 x U(1)_FN, whose choice is motivated by the approximate Tri-Bimaximal mixing observed in neutrino oscillations. A low-energy effective Lagrangian is constructed, where these effects are dominated by dimension six operators, suppressed by the scale M of new physics. All the flavour breaking effects are universally described by the vacuum expectation values of a set of spurions. Two separate cases, a supersymmetric and a general one, are described. An upper limit on the reactor angle of a few percent is concluded.
On discrete Minimal Flavour Violation
2009-08-31
We investigate the consequences of replacing the global flavour symmetry of Minimal Flavour Violation (MFV), SU(3)_QxSU(3)_UxSU(3)_Dx..., by a discrete D_QxD_UxD_Dx.. symmetry. Our primary motivation of this investigation is the absence of Goldstone bosons for spontaneously broken discrete symmetries. Less symmetry implies further invariants and renders the mass flavour basis transformation observable in principle and calls for a hierarchy in the Yukawa matrix expansion. We show, through the dimension of the representations, that the (discrete) symmetry in principle does allow for additional \Delta F = 2 operators. If though the \Delta F = 2 transitions are generated by two subsequent \Delta F = 1 processes, as for example in the Standard Model, then the four crystal-like groups \Sigma(168) ~ PSL(2,7), \Sigma(72phi), \Sigma(216phi) and especially \Sigma(360phi) do provide enough protection for a TeV-scale discrete MFV scenario. Models where this is not the case have to be investigated case by case. Interestingly \Sigma(216phi) has a (non-faithful) representation corresponding to an A4-symmetry. Moreover we argue that the, apparently often omitted, (D)-groups are subgroups of an appropriate \Delta(6g^2). We would like to stress that we do not provide an actual model that realizes the MFV scenario nor any other theory of flavour.
2009-05-07
The introduction of a Flavour Symmetry can represent an interesting way in which one can try to find an answer to some intriguing problems in Flavour Physics, like the hierarchy between the fermion masses or the particular values of mixing angles. In the meantime the necessity to set this symmetry in a realistic context grows up; this context should be able to enlarge our incomplete knowledge of fundamental interactions as described in the framework of the Standard Model. Following this direction a merging between A(4) and SU(5) can be possible.
Maximal Neutrino Mixing from Discrete Symmetry in Extra Dimensions
2005-12-01
I review the construction of a model for lepton masses based on the flavour symmetry group A4 x U(1) reproducing the so-called tri-bimaximal lepton mixing scheme, in eccelent agreement with current data. The model predicts a neutrino spectrum of normal hierarchy type, not far from degenerate. A testable relation between neutrino masses is obtained. I shortly discuss also general requirements for models based on spontaneously broken flavour symmetries, in order to get a maximal atmospheric mixing angle.
A4 family symmetry and quark-lepton unification
2006-10-19
We present a model of quark and lepton masses and mixings based on A4 family symmetry, a discrete subgroup of an SO(3) flavour symmetry, together with Pati-Salam unification. It accommodates tri-bimaximal neutrino mixing via constrained sequential dominance with a particularly simple vacuum alignment mechanism emerging through the effective D-term contributions to the scalar potential.
Neutrino Physics and A4 matter assignments
2008-07-28
Tribimaximal lepton mixing can be obtained assuming A4 flavour symmetry. Many possibilities have been explored in the literature and we give a classification in terms of A4 representations. We propose some phenomenological and theoretical criteria to distinguish between different assignment. As example we consider the possibility to extend A4 to SO(10) grand unified model.
Discrete symmetries of lepton mixing angles
2006-01-01
Lepton mixing angles are very well described by the so-called tri-bimaximal mixing scheme proposed by Harrison, Perkins and Scott. I show how such a mixing pattern can be derived starting from a discrete flavour symmetry based on the symmetry group A4 and closely related to the modular group. As a consequence, a testable relation between neutrino masses is obtained
Running Effects on Lepton Mixing Angles in Flavour Models with Type I Seesaw
2009-11-17
We study renormalization group running effects on neutrino mixing patterns when a (type I) seesaw model is implemented by suitable flavour symmetries. We are particularly interested in mass-independent mixing patterns to which the widely studied tribimaximal mixing pattern belongs. In this class of flavour models, the running contribution from neutrino Yukawa coupling, which is generally dominant at energies above the seesaw threshold, can be absorbed by a small shift on neutrino mass eigenvalues leaving mixing angles unchanged. Consequently, in the whole running energy range, the change in mixing angles is due to the contribution coming from charged lepton sector. Subsequently, we analyze in detail these effects in an explicit flavour model for tribimaximal neutrino mixing based on an A4 discrete symmetry group. We find that for normally ordered light neutrinos, the tribimaximal prediction is essentially stable under renormalization group evolution. On the other hand, in the case of inverted hierarchy, the deviation of the solar angle from its TB value can be large depending on mass degeneracy.
A Simplest A4 Model for Tri-Bimaximal Neutrino Mixing
2009-05-06
We present a see-saw $A_4$ model for Tri-Bimaximal mixing which is based on a very economical flavour symmetry and field content and still possesses all the good features of $A_4$ models. In particular the charged lepton mass hierarchies are determined by the $A_4\times Z_4$ flavour symmetry itself without invoking a Froggatt-Nielsen U(1) symmetry. Tri-Bimaximal mixing is exact in leading order while all the mixing angles receive corrections of the same order in next-to-the-leading approximation. As a consequence the predicted value of $\theta_{13}$ is within the sensitivity of the experiments which will take data in the near future. The light neutrino spectrum, typical of $A_4$ see-saw models, with its phenomenological implications, also including leptoproduction, is studied in detail.
Vacuum Alignment in SUSY A4 Models
2009-10-22
In this note we discuss the vacuum alignment in supersymmetric models with spontaneously broken flavour symmetries in the presence of soft supersymmetry (SUSY) breaking terms. We show that the inclusion of soft SUSY breaking terms can give rise to non-vanishing vacuum expectation values (VEVs) for the auxiliary components of the flavon fields. These non-zero VEVs can have an important impact on the phenomenology of this class of models, since they can induce an additional flavour violating contribution to the sfermion soft mass matrix of right-left (RL) type. We carry out an explicit computation in a class of SUSY A4 models predicting tri-bimaximal mixing in the lepton sector. The flavour symmetry breaking sector is described in terms of flavon and driving supermultiplets. We find non-vanishing VEVs for the auxiliary components of the flavon fields and for the scalar components of the driving fields which are of order m_{SUSY} x and m_{SUSY}, respectively. Thereby, m_{SUSY} is the generic soft SUSY breaking scale which is expected to be around 1 TeV and is the VEV of scalar components of the flavon fields. Another effect of these VEVs can be the generation of a mu term.
Resonant leptogenesis and tribimaximal leptonic mixing with A4 symmetry
2009-04-21
We investigate the viability of thermal leptogenesis in type-I seesaw models with leptonic flavour symmetries that lead to tribimaximal neutrino mixing. We consider an effective theory with an A4 x Z3 x Z4 symmetry, which is spontaneously broken at a scale much higher than the electroweak scale. At the high scale, leptonic Yukawa interactions lead to exact tribimaximal mixing and the heavy Majorana neutrino mass spectrum is exactly degenerate. In this framework, leptogenesis becomes viable once this degeneracy is lifted either by renormalization group effects or by a soft breaking of the A4 symmetry. The implications for low-energy neutrino physics are discussed.
Inverse tri-bimaximal type-III seesaw and lepton flavor violation
2009-07-20
We present a type-III version of inverse seesaw or, equivalently an inverse version of type-III seesaw. Naturally small neutrino masses arise at low-scale from the exchange of neutral fermions transforming as hyperchargeless SU(2) triplets. In order to implement tri-bimaximal lepton mixing we supplement the minimal SU(3)xSU(2)xU(1) gauge symmetry with an A4-based flavor symmetry. Our scenario induces lepton flavour violating (LFV) three body decays that can proceed at the tree level, while radiative li to lj gamma decays and mu-e conversion in nuclei are also expected to be sizeable. LFV decays are related by the underlying flavor symmetry and the new fermions are also expected to be accessible for study at the Large Hadron Collider (LHC).
Phenomenological Consequences of See-Saw in S4 Based Models
2009-02-18
It has recently appeared a flavour model based on the symmetry group S4, managing to describe fermion masses and mixings. The Weinberg operator has been used in order to provide the smallness of the neutrino masses, while a set of scalar fields, getting non-vanishing vacuum expectation values, spontaneously breaks down S4 and provides the Tri-Bimaximal pattern as the lepton mixing matrix. In this paper we analyze possible explanations for the effective terms: the type I See-Saw mechanism is the simplest approach, but also the type II and III are discussed. The phenomenology related to these models is extremely various and the next future experiments could discriminate among these proposals. Furthermore, we compare our realizations to some relevant A4 based models, still predicting the Tri-Bimaximal lepton mixing, and we found that an analysis on the neutrinoless double beta decay parameters could distinguish among all these realizations. Furthermore a combined measurement of the effective mass and of the lightest neutrino mass could indicate in the next future which is the preferred flavour symmetry group. The introduction of new beyond Standard Model physics, like heavy right-handed neutrinos, scalar triplets and fermion triplets, let us investigate on leptogenesis and this provides some constraints in the realization of the models.
The use of menthol in cigarettes is actively promoted by the tobacco industry for its per-ceived sensory benefits, and smokers of menthol cigarettes commonly differ from nonmen-thol smokers in markers of smoking behavior and addiction.
Topics in electroweak baryogenesis: The sphaleron and t-violation
Assuming that beyond the standard model physics can be parametrized in terms of high dimensional operators, we examine their effects on the energy of the sphaleron and the classical solution of the gauge and Higgs fields. In the absence of fermions, all of the six dimension 6 operators which are SU(2) symmetric have a small effect when calculated perturbatively. However, calculated non-perturbatively, one of the operators alters the boundary conditions of the equations of motion of the Higgs and gauge fields involved, and another operator gives rise to an abrupt change in the sphaleron energy at a small but definite Higgs quartic coupling. The magnitude of the T-violating muon polarization induced by electromagnetic final state interaction in the radiative Kaon decay K{sup +} {yields} {mu}{sup +}{nu}{mu}{gamma} is order of 10{sup {minus}3}.
2004-04-15
The QCD non-perturbative effects are among the main sources of uncertainty in our present knowledge of the Standard Model phenomenology. I will present some of the methods which can be used to study these effects, and I will particularly treat the case of lattice QCD. Effective theories can be combined to the lattice approach in order to study the chiral and the heavy quark sectors. I will give some examples of how these properties can be successfully applied to the quark flavour phenomenology. The coupling of heavy mesons to the pion is related to a non-perturbative quantity, noted g-bar, which is required to extract physical results from the effective theory combining both chiral and heavy quark symmetry. This coupling is also involved in the study of the form factors appearing in the heavy to light semi-leptonic decays. These heavy meson decays are used to extract some of the CKM matrix elements which are know, up to now, only with large uncertainties. Moreover, the chiral effects of heavy mesons depend on pion loops whose vertices are precisely the coupling g-bar. These are some of the reasons why the theoretical and experimental determination of this coupling is required. I will present the results of its studies on the lattice and I will compare them to those obtained through several other methods. I will therefore describe these different approaches, their limitations and possible improvements, both from the point of view of the method and of its application to the determination of the coupling g-bar. (author)
The Schroedinger functional for Gross-Neveu models
2007-04-18
Gross-Neveu type models with a finite number of fermion flavours are studied on a two-dimensional Euclidean space-time lattice. The models are asymptotically free and are invariant under a chiral symmetry. These similarities to QCD make them perfect benchmark systems for fermion actions used in large scale lattice QCD computations. The Schroedinger functional for the Gross-Neveu models is defined for both, Wilson and Ginsparg-Wilson fermions, and shown to be renormalisable in 1-loop lattice perturbation theory. In two dimensions four fermion interactions of the Gross-Neveu models have dimensionless coupling constants. The symmetry properties of the four fermion interaction terms and the relations among them are discussed. For Wilson fermions chiral symmetry is explicitly broken and additional terms must be included in the action. Chiral symmetry is restored up to cut-off effects by tuning the bare mass and one of the couplings. The critical mass and the symmetry restoring coupling are computed to second order in lattice perturbation theory. This result is used in the 1-loop computation of the renormalised couplings and the associated beta-functions. The renormalised couplings are defined in terms of suitable boundary-to-boundary correlation functions. In the computation the known first order coefficients of the beta-functions are reproduced. One of the couplings is found to have a vanishing betafunction. The calculation is repeated for the recently proposed Schroedinger functional with exact chiral symmetry, i.e. Ginsparg-Wilson fermions. The renormalisation pattern is found to be the same as in the Wilson case. Using the regularisation dependent finite part of the renormalised couplings, the ratio of the Lambda-parameters is computed. (orig.)
1995-11-01
The author has studied production of strange and multistrange baryons and antibaryons in central sulphur-tungsten, sulphur-sulphur, and lead-lead interactions at relativistic energies. The spectra of strange baryons and antibaryons provide information about the dynamics of hadronic matter under the extreme conditions realised in these collisions. The particle ratios allow the degree and the nature of the flavour equilibrium to be studied, while the transverse mass distributions provide independent information of the temperatures achieved. 143 refs.
Results on {alpha}{sub s} and QCD from (and above) the Z{sup 0}
In electron-positron annihilation hadronic activity is, by construction, limited to the final state, making the study of hadronic events cleaner and simpler relative to lepton-hadron and hadron-hadron collisions, from both the experimental and theoretical points-of-view. To be specific, samples of hadronic events can be selected by experiments at the Z{sup 0} resonance with efficiency and purity of better than 99%. Jet and event-shape observables have been calculated at next-to-leading order, O({alpha}{sub s}{sup 2}), and some inclusive observables have been calculated at O({alpha}{sub s}{sup 3}). Non-perturbative calculations, in the form of power corrections to perturbatively-evaluated observables, have been performed, and there are well-understood models of hadronization that have been carefully tuned to the data collected over the past 20 years. Electron-positron annihilation thus provides an ideal environment for precise tests of QCD, and has yielded spectacular results. Here, measurements of {alpha}{sub s} from e{sup +}e{sup {minus}} annihilation experiments are reviewed and compared with measurements from other processes. Highlights are presented of recent QCD studies in e{sup +}e{sup {minus}} annihilation at the Z{sup 0} resonance.
Quasi-degenerate neutrinos from an abelian family symmetry
The authors show that models with an abelian family symmetry which accounts for the observed hierarchies of masses and mixings in the quark sector may also accommodate quasi-degeneracies in the neutrino mass spectrum. Such approximate degeneracies are, in this context, associated with large mixing angles. The parameters of this class of models are constrained. The authors discuss their phenomenological implications for present and foreseen neutrino experiments.
Quasi-degenerate neutrinos from an abelian family symmetry
1996-12-31
The authors show that models with an abelian family symmetry which accounts for the observed hierarchies of masses and mixings in the quark sector may also accommodate quasi-degeneracies in the neutrino mass spectrum. Such approximate degeneracies are, in this context, associated with large mixing angles. The parameters of this class of models are constrained. The authors discuss their phenomenological implications for present and foreseen neutrino experiments.
QCD bound states and their response to extremes of temperature and density.
We describe the application of Dyson-Schwinger equations to the calculation of hadron observable. The studies at zero temperature (T) and quark chemical potential ({mu}) provide a springboard for the extension to finite-(T, {mu}). Our exemplars highlight that much of hadronic physics can be understood as simply a manifestation of the nonperturbative, momentum-dependent dressing of the elementary Schwinger functions in QCD.
2007-09-15
The following topics were dealt with: QCD parton dynamics, results form the H1 and ZEUS experiments at HERA, the spin structure of the nucleon, QCD Monte Carlo generators, results from the Jefferson Lab, lattice QCD, results from the Tevatron, heavy flavour production, the fluid nature of the quark-gluon plasma, QCD dynamics in hadrons and nuclei at high energies, QCD and string theory, structure functions, electroweak measurements, physics beyond the Standard Model, diffraction and vector mesons, spin physics. (HSI)
2009-04-09
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.)
Optimised Dirac operators on the lattice. Construction, properties and applications
2006-11-15
We review a number of topics related to block variable renormalisation group transformations of quantum fields on the lattice, and to the emerging perfect lattice actions. We first illustrate this procedure by considering scalar fields. Then we proceed to lattice fermions, where we discuss perfect actions for free fields, for the Gross-Neveu model and for a supersymmetric spin model. We also consider the extension to perfect lattice perturbation theory, in particular regarding the axial anomaly and the quark gluon vertex function. Next we deal with properties and applications of truncated perfect fermions, and their chiral correction by means of the overlap formula. This yields a formulation of lattice fermions, which combines exact chiral symmetry with an optimisation of further essential properties. We summarise simulation results for these so-called overlap-hypercube fermions in the two-flavour Schwinger model and in quenched QCD. In the latter framework we establish a link to Chiral Perturbation Theory, both, in the p-regime and in the epsilon-regime. In particular we present an evaluation of the leading Low Energy Constants of the chiral Lagrangian - the chiral condensate and the pion decay constant - from QCD simulations with extremely light quarks. (orig.)
Nonperturbative QCD with modern tools
In these lectures the author introduces and explores a range of topics of contemporary interest in hadronic physics: from what drives the formation of a nonzero quark condensate to the effect that mechanism has on light and heavy meson form factors and the properties of the quark-gluon plasma. The trail leads naturally through a discussion of confinement, dynamical chiral symmetry breaking and bound state structure: phenomena that require nonperturbative methods for their explanation. In all of this, the necessary and necessarily momentum-dependent modification of the quark and gluon propagators plays a significant role.
Nonperturbative QCD with modern tools
1998-07-01
In these lectures the author introduces and explores a range of topics of contemporary interest in hadronic physics: from what drives the formation of a nonzero quark condensate to the effect that mechanism has on light and heavy meson form factors and the properties of the quark-gluon plasma. The trail leads naturally through a discussion of confinement, dynamical chiral symmetry breaking and bound state structure: phenomena that require nonperturbative methods for their explanation. In all of this, the necessary and necessarily momentum-dependent modification of the quark and gluon propagators plays a significant role.
2007-09-15
The purpose of this thesis is to study, in the neutrino sector, the flavour structures at high energy. The work is divided into two main parts. The first part is dedicated to the well known mechanism to produce small neutrino masses: the seesaw mechanism, which implies the existence of massive particles whose decays violate lepton number. Therefore this mechanism can also be used to generate a net baryon number in the early universe and explain the cosmological observation of the asymmetry between matter and antimatter. However, it is often non-trivial to fulfill the constraints coming at the same time from neutrino oscillations and cosmological experiments, at least in frameworks where the couplings can be somehow constrained, like some Grand Unification models. Therefore we devoted the first part to the study of a certain class of seesaw mechanism which can be found in the context of SO(10) theories for example. We introduce a method to extract the mass matrix of the heavy right-handed neutrinos and explore the phenomenological consequences of this quantity, mainly concerning the production of a sufficient baryon asymmetry. When trying to identify the underlying symmetry governing the mixings between the different generations, we see that there is a puzzling difference between the quark and the lepton sectors. However, the quark and lepton parameters have to be compared at the scale of the flavour symmetry breaking, therefore we have to make them run to the appropriate scale. Thus, it is worthwhile investigating models where quantum corrections allow an approximate unification of quark and lepton mixings. This is why the other part of the thesis investigates the running of the effective neutrino mass operator in models with an extra compact dimension, where quantum corrections to the neutrino masses and mixings can be potentially large due to the multiplicity of states.
NCI Funded Research Portfolio - 1R43CA121646-01A2 Detail
Your source for National Cancer Institute funded research grants, contract awards, and intramural research projects. More Home Advanced Search About NFRP Contact Us Help Viewing Project « Back to results Link to this Project Print Help Copy this URL
2007-01-16
We study flavor-changing decays of hadrons and leptons and an extra-dimensional approach to electroweak symmetry breaking. Specifically we study the framework of Minimal Flavour Violation (MFV) as an explanation of the flavour problem. We discuss the impact of a specific extra-dimensional model of the MFV class on flavour changing neutral currents. We derive model-independent upper bounds on rare decays. -We discuss the extension of the MFV framework from the quark to the lepton sector and show how baryogenesis through leptogenesis can be achieved and examine if possible correlations with charged lepton flavour violation exist. We discuss the dynamical breaking of the electroweak symmetry in extra dimensions by unifying gauge and Higgs fields and we show that realistic models are possible once the extra dimension is strongly curved. (orig.)
Serving Size for the Milks on Cereal Serving size for the milks on cereal will be handled in the same way as regular food items.
133 Detailed studies of inbred mouse strains have provided remarkable insights into how genetics shape complex processes, ranging from cancer susceptibility to immunity. The mouse models of response to addictive substances such as nicotine are now showing
Heavy quark symmetry: Theory and applications
This report very briefly discusses heavy quark symmetry.
Heavy quark symmetry: Theory and applications
1993-07-30
This report very briefly discusses heavy quark symmetry.
Heavy meson observables via Dyson-Schwinger equations
The authors summarize a Dyson-Schwinger-equation-based calculation of an extensive range of light- and heavy-meson observable, characterized by heavy-meson leptonic decays, semileptonic heavy-to-heavy and heavy-to-light transitions--B {yields} D*, D, {rho}, {pi}; D {yields} K*, K, {pi}, radiative and strong decays--B*{sub (s)} {yields} B{sub (s)}{gamma}; D*{sub (s)}{gamma} and the rare B {yields} K*{sub {gamma}} flavor-changing neutral-current process. In the calculation the heavy-quark mass functions are approximated by constants, interpreted as their constituent-mass: {cflx M}{sub c} = 1.32GeV and {cflx M}{sub b} = 4.65 GeV.
Gauge-Higgs unification with broken flavour symmetry
2007-05-15
We study a five-dimensional Gauge-Higgs unification model on the orbifold S{sup 1}/Z{sub 2} based on the extended standard model (SM) gauge group SU(2){sub L} x U(1){sub Y} x SO(3){sub F}. The group SO(3){sub F} is treated as a chiral gauged flavour symmetry. Electroweak-, flavour- and Higgs interactions are unified in one single gauge group SU(7). The unified gauge group SU(7) is broken down to SU(2){sub L} x U(1){sub Y} x SO(3){sub F} by orbifolding and imposing Dirichlet and Neumann boundary conditions. The compactification scale of the theory is O(1) TeV. Furthermore, the orbifold S{sup 1}/Z{sub 2} is put on a lattice. This setting gives a well-defined staring point for renormalisation group (RG) transformations. As a result of the RG-flow, the bulk is integrated out and the extra dimension will consist of only two points: the orbifold fixed points. The model obtained this way is called an effective bilayered transverse lattice model. Parallel transporters (PT) in the extra dimension become nonunitary as a result of the blockspin transformations. In addition, a Higgs potential V({phi}) emerges naturally. The PTs can be written as a product e{sup A{sub y}}e{sup {eta}}e{sup A{sub y}} of unitary factors e{sup A{sub y}} and a selfadjoint factor e{sup {eta}}. The reduction 48 {yields} 35 + 6 + anti 6 + 1 of the adjoint representation of SU(7) with respect to SU(6) contains SU(2){sub L} x U(1){sub Y} x SO(3){sub F} leads to three SU(2){sub L} Higgs doublets: one for the first, one for the second and one for the third generation. Their zero modes serve as a substitute for the SM Higgs. When the extended SM gauge group SU(2){sub L} x U(1){sub Y} x SO(3){sub F} is spontaneously broken down to U(1){sub em}, an exponential gauge boson mass splitting occurs naturally. At a first step SU(2){sub L} x U(1){sub Y} x SO(3){sub F} is broken to SU(2){sub L} x U(1){sub Y} by VEVs for the selfadjoint factor e{sup {eta}}. This breaking leads to masses of flavour changing SO(3){sub F} gauge bosons much above the compactification scale. Such a behaviour has no counterpart within the customary approximation scheme of an ordinary orbifold theory. This way tree-level flavour-changing-neutral-currents are naturally suppressed. In a second step the electroweak gauge group SU(2){sub L} x U(1){sub Y} is broken to U(1){sub em} by VEVs for the unitary factors e{sup A{sub y}} at the electroweak scale. This breaking is equivalent to a Wilson line breaking. Making some simplifying assumptions we also calculate fermion masses and CKM mixing angles. As for the gauge bosons an exponential fermion mass splitting occurs naturally. Fermion masses and mixing angles are determined by the VEVs for e{sup {eta}} and e{sup A{sub y}} of PTs for quarks and leptons. The model predicts a large Higgs sector consisting of altogether 30 Higgs particles. The model in its simplest form also predicts the (too small) weak mixing angle {theta}{sub W}=0.125. (orig.)
C1. Establish a formal project management system for early translational research. C2. Establish a system to coordinate core services essential for early translational research. C3.
We present results for the static interquark potential, light meson and baryon masses, and light pseudoscalar meson decay constants obtained from simulations of domain wall QCD with one dynamical flavour approximating the $s$ quark, and two degenerate dynamical flavours with input bare masses ranging from $m_s$ to $m_s/4$ approximating the $u$ and $d$ quarks. We compare these quantities obtained using the Iwasaki and DBW2 improved gauge actions, and actions with larger rectangle coefficients, on $16^3\times32$ lattices. We seek parameter values at which both the chiral symmetry breaking residual mass due to the finite lattice extent in the fifth dimension and the Monte Carlo time history for topological charge are acceptable for this set of quark masses at lattice spacings above 0.1 fm. We find that the Iwasaki gauge action is best, demonstrating the feasibility of using QCDOC to generate ensembles which are good representations of the QCD path integral on lattices of up to 3 fm in spatial extent with lattice spacings in the range 0.09-0.13 fm. Despite large residual masses and a limited number of sea quark mass values with which to perform chiral extrapolations, our results for light hadronic physics scale and agree with experimental measurements within our statistical uncertainties.
2007-06-01
We present results for the static interquark potential, light meson and baryon masses, and light pseudoscalar meson decay constants obtained from simulations of domain wall QCD with one dynamical flavour approximating the $s$ quark, and two degenerate dynamical flavours with input bare masses ranging from $m_s$ to $m_s/4$ approximating the $u$ and $d$ quarks. We compare these quantities obtained using the Iwasaki and DBW2 improved gauge actions, and actions with larger rectangle coefficients, on $16^3\times32$ lattices. We seek parameter values at which both the chiral symmetry breaking residual mass due to the finite lattice extent in the fifth dimension and the Monte Carlo time history for topological charge are acceptable for this set of quark masses at lattice spacings above 0.1 fm. We find that the Iwasaki gauge action is best, demonstrating the feasibility of using QCDOC to generate ensembles which are good representations of the QCD path integral on lattices of up to 3 fm in spatial extent with lattice spacings in the range 0.09-0.13 fm. Despite large residual masses and a limited number of sea quark mass values with which to perform chiral extrapolations, our results for light hadronic physics scale and agree with experimental measurements within our statistical uncertainties.
Fermion masses and mixing in 331 models with horizontal symmetry
1997-12-31
The possibility of adding an SU (2) horizontal symmetry to the 331 model is studied. It is found that simple, anomaly-free fermion assignments can be made which lead to plausible results for fermion masses and mixings. In particular, all particles of the first generation are massless at tree-level, and the Cabibbo-Kobayashi-Maskawa (CKM) matrix acquires a realistic form. (authors). 16 refs.
Estimated Number of New Cancer Cases in 1990 By Racial / Ethnic Group
National Cancer Institute A-4 SEER Program APPENDIX 2. Estimated Number of New Cases of Selected Cancers in the United States by Racial/Ethnic Group, 1990 - Men (Estimates derived by multiplying ?average annual? age-specific incidence rates for the
Dynamical electroweak symmetry breaking and the top quark
1997-01-01
In this talk, I discuss theories of dynamical electroweak symmetry breaking, with emphasis on the implications of a heavy top quark on the weak interaction {rho} parameter.
Description of hot compressed hadronic matter based on an effective chiral Lagrangian
1996-11-01
In this report we give the review of the recent results obtained in the Nambu-Jona-Lasinio (NJL) model, describing the properties of hot compressed matter. The first large class problems concerns the behaviour of static meson correlation functions. In particular, this includes the investigation of the screening of meson fields at finite temperature or density. Another wide range of problems presented in our report concerns the formulation of the transport theory for the NJL model and its applications to the description of high energy nuclear collision. 86 refs, 35 figs.
Continuum strong QCD: Confinement and dynamical chiral symmetry breaking
Continuum strong QCD is the application of models and continuum quantum field theory to the study of phenomena in hadronic physics, which includes; e.g., the spectrum of QCD bound states and their interactions. Herein the author provides a Dyson-Schwinger equation perspective, focusing on qualitative aspects of confinement and dynamical chiral symmetry breaking in cold, sparse QCD, and also elucidating consequences of the axial-vector Ward-Takahashi identity and features of the heavy-quark limit.
Continuum strong QCD: Confinement and dynamical chiral symmetry breaking
2000-07-24
Continuum strong QCD is the application of models and continuum quantum field theory to the study of phenomena in hadronic physics, which includes; e.g., the spectrum of QCD bound states and their interactions. Herein the author provides a Dyson-Schwinger equation perspective, focusing on qualitative aspects of confinement and dynamical chiral symmetry breaking in cold, sparse QCD, and also elucidating consequences of the axial-vector Ward-Takahashi identity and features of the heavy-quark limit.
Clover improvement for stout-smeared 2+1 flavour SLiNC fermions. Perturbative results
2008-09-15
For the Stout Link Non-perturbative Clover (SLiNC) action we determine in one-loop lattice perturbation theory the critical hopping parameter {kappa}{sub c} and the clover parameter c{sub sw} which is needed for O(a) improvement. Performing this calculation off-shell we are also able to compute the non gauge invariant quark field improvement coefficient c{sub NGI}. Additionally, we present first results for the renormalization factors of the scalar, pseudoscalar, vector and axial vector currents. We discuss mean field improvement for the SLiNC action. (orig.)
Argus-Fest. 20 years of B meson mixing 1987-2007. Proceedings
2007-11-15
The following topics were dealt with: ARGUS data, launching DORIS and ARGUS, B physics, discovery of B mixing, sociology of the ARGUS collaboration, CLEO B physics, from ARGUS to B-meson factories, the B factory era, B physics at the Tevatron, future of B physics programs, future of flavour physics. (HSI)
Alabama 4,485,435 2,170,273 2,315,162 3,236,506 1,587,622 1,648,884 1,187,005 552,325 634,681 Alaska 641,343 331,563 309,780 468,618 244,977 223,641 28,422 14,871 13,551 Arizona 5,443,549 2,720,624 2,722,924 4,816,467 2,409,224 2,407,243 203,309 105,620 97,689 Arkansas 2,710,573 1,325,597 1,384,976 2,230,796 1,098,184 1,132,612 433,718 205,022 228,696 California 34,963,229 17,437,532 17,525,697 27,476,181 13,792,779 13,683,402 2,557,804 1,254,555 1,303,248 Colorado 4,480,448 2,258,763 2,221,685 4,096,581 2,065,157 2,031,424 200,175 104,032 96,143 Connecticut 3,457,591 1,676,690 1,780,901 2,982,324 1,447,935 1,534,389 358,133 170,703 187,429 Delaware 807,104 392,640 414,464 617,889 302,481 315,408 165,571 78,601 86,969 Dist.
Antineoplastons (PDQ®) (Patient)
Expert-reviewed information summary about antineoplastons as a treatment for cancer.
Antineoplastons (PDQ®) (Health Professional)
Expert-reviewed information summary about antineoplastons as a treatment for cancer.
2006-04-15
We discuss the renormalisation properties of the complete set of {delta}B=2 four-quark operators with the heavy quark treated in the static approximation. We elucidate the role of heavy quark symmetry and other symmetry transformations in constraining their mixing under renormalisation. By employing the Schroedinger functional, a set of non-perturbative renormalisation conditions can be defined in terms of suitable correlation functions. As a first step in a fully non-perturbative determination of the scale-dependent renormalisation factors, we evaluate these conditions in lattice perturbation theory at one loop. Thereby we verify the expected mixing patterns and determine the anomalous dimensions of the operators at NLO in the Schroedinger functional scheme. Finally, by employing twisted-mass QCD it is shown how finite subtractions arising from explicit chiral symmetry breaking can be avoided completely. (Orig.)
Albert Einstein College of Medicine, New York, New York Abstract Approximately 15 human papillomavirus (HPV) types cause virtually all cervical cancer whereas other HPV types are unrelated to cancer. We were interested in whether some noncarcinogenic types differ from carcinogenic in their affinity for the cervical transformation zone, where nearly all HPV-induced cancers occur.
Website Policies and Important Links Comments
 |
 |
 |
WorldWideScience.org is maintained by the
U.S. Department of Energy's
Office of Scientific and Technical Information as the Operating Agent
for the WorldWideScience Alliance.