Evolution of curvature perturbation in generalized gravity theories
Energy Technology Data Exchange (ETDEWEB)
Matsuda, Tomohiro, E-mail: matsuda@sit.ac.j [Laboratory of Physics, Saitama Institute of Technology, Fusaiji, Okabe-machi, Saitama 369-0293 (Japan)
2009-07-21
Using the cosmological perturbation theory in terms of the deltaN formalism, we find the simple formulation of the evolution of the curvature perturbation in generalized gravity theories. Compared with the standard gravity theory, a crucial difference appears in the end-boundary of the inflationary stage, which is due to the non-ideal form of the energy-momentum tensor that depends explicitly on the curvature scalar. Recent study shows that ultraviolet-complete quantum theory of gravity (Horava-Lifshitz gravity) can be approximated by using a generalized gravity action. Our paper may give an important step in understanding the evolution of the curvature perturbation during inflation, where the energy-momentum tensor may not be given by the ideal form due to the corrections from the fundamental theory.
Extended Theories of Gravity with Generalized Energy Conditions
Mimoso, José P; Capozziello, Salvatore
2014-01-01
We address the problem of the energy conditions in modified gravity taking into account the additional degrees of freedom related to scalar fields and curvature invariants. The latter are usually interpreted as generalized {\\it geometrical fluids} that differ in meaning with respect to the matter fluids generally considered as sources of the field equations. In extended gravity theories the curvature terms are encapsulated in a tensor $H^{ab}$ and a coupling $g(\\Psi^i)$ that can be recast as effective Einstein field equations, with corrections to the energy-momentum tensor of matter. The formal validity of standard energy inequalities does not assure basic requirements such as the attractive nature of gravity, so we argue that the energy conditions have to be considered in a wider sense.
Generalized energy conditions in Extended Theories of Gravity
Capozziello, Salvatore; Mimoso, José P
2014-01-01
Theories of physics can be considered viable if the initial value problem and the energy conditions are formulated self-consistently. The former allow a uniquely determined dynamical evolution of the system, and the latter guarantee that causality is preserved and that "plausible" physical sources have been considered. In this work, we consider the further degrees of freedom related to curvature invariants and scalar fields in Extended Theories of Gravity (ETG). These new degrees of freedom can be recast as effective perfect fluids that carry different meanings with respect to the standard matter fluids generally adopted as sources of the field equations. It is thus somewhat misleading to apply the standard general relativistic energy conditions to this effective energy-momentum, as the latter contains the matter content and a geometrical quantity, which arises from the ETG considered. Here, we explore this subtlety, extending on previous work, in particular, to cases with the contracted Bianchi identities wi...
Linker, Patrick
2016-01-01
A couple of quantum gravity theories were proposed to make theoretical predictions about the behavior of gravity. The most recent approach to quantum gravity, called E-theory, is proposed mathematical, but there is not formulated much about what dynamics of gravity this theory proposes. This research paper treats the main results of the application of E-theory to General relativity involving conservation laws and scattering of particles in presence of gravity. Also the low-energy limit of thi...
Gauge-ready formulation of the cosmological kinetic theory in generalized gravity theories
Hwang, J
2002-01-01
We present cosmological perturbations of kinetic components based on relativistic Boltzmann equations in the context of generalized gravity theories. Our general theory considers an arbitrary number of scalar fields generally coupled with the gravity, an arbitrary number of mutually interacting hydrodynamic fluids, and components described by the relativistic Boltzmann equations like massive/massless collisionless particles and the photon. The model includes the general background spatial curvature and the cosmological constant. We consider three different types of perturbations, and all the scalar-type perturbation equations are arranged in a gauge-ready form so that one can implement easily the convenient gauge conditions depending on the situation. In the numerical calculation of the Boltzmann equations we found two new gauge conditions (the uniform-expansion gauge and the uniform-curvature gauge) which show better behavior than the previously employed gauge conditions in the literature. In particular, we ...
Gravitational Wave Spectrums from Pole-like Inflations based on Generalized Gravity Theories
Hwang, J
1998-01-01
We present a general and unified formulation which can handle the classical evolution and quantum generation processes of the cosmological gravitational wave in a broad class of generalized gravity theories. Applications are made in several inflation models based on the scalar-tensor theory, the induced gravity, and the low energy effective action of string theory. The gravitational wave power spectrums based on the vacuum expectation value of the quantized fluctuating metric during the pole-like inflation stages are derived in analytic forms. Assuming that the gravity theory transits to Einstein one while the relevant scales remain in the superhorizon scale, we derive the consequent power spectrums and the directional fluctuations of the relic radiation produced by the gravitational wave. The spectrums seeded by the vacuum fluctuations in the pole-like inflation models based on the generalized gravity show a distinguished common feature which differs from the scale invariant spectrum generated in an exponent...
General Stationary, Spherically-Symmetric Solutions in the Gauge Theory of Gravity
Francis, M R; Francis, Matthew R.; Kosowsky, Arthur
2003-01-01
This paper provides a concise overview of the gauge theory of gravity, as recently formulated by Lasenby, Doran, and Gull. Instead of representing gravitation via spacetime curvature, the effects of gravity are given by gauge fields in flat spacetime; the gauge group is that of Lorentz transformations plus covariance under diffeomorphisms. The resulting theory is formally similar to the Cartan formulation of general relativity, and we make detailed comparisons with conventional representations of general relativity. We provide a constructive method for solving the field equations in gauge theory gravity, and apply this method to the spherically symmetric case. The most general vacuum solution results, which explicitly displays all coordinate freedom in terms of free functions of radius. Through particular choices of these functions, our general solution reduces to all known metric representations of spherically symmetric, stationary vacuum spacetime. We also obtain the corresponding generalization of the Reis...
Radioscience simulations in General Relativity and in alternative theories of gravity
Hees, A; Reynaud, S; Jaekel, M -T; Poncin-Lafitte, C Le; Lainey, V; Füzfa, A; Courty, J -M; Dehant, V; Wolf, P
2012-01-01
In this paper, we focus on the possibility to test General Relativity in the Solar System with radioscience measurements. To this aim, we present a new software that simulates Range and Doppler signals directly from the space-time metric. This flexible approach allows one to perform simulations in General Relativity and in alternative metric theories of gravity. In a second step, a least-squares fit of the different initial conditions involved in the situation is performed in order to compare anomalous signals produced by a given alternative theory with the ones obtained in General Relativity. This software provides orders of magnitude and signatures stemming from hypothetical alternative theories of gravity on radioscience signals. As an application, we present some simulations done for the Cassini mission in Post-Einsteinian Gravity and in the context of MOND External Field Effect. We deduce constraints on the Post-Einsteinian parameters but find that the considered arc of the Cassini mission is not useful ...
Capozziello, Salvatore
2011-01-01
Extended Theories of Gravity can be considered a new paradigm to cure shortcomings of General Relativity at infrared and ultraviolet scales. They are an approach that, by preserving the undoubtedly positive results of Einstein's Theory, is aimed to address conceptual and experimental problems recently emerged in Astrophysics, Cosmology and High Energy Physics. In particular, the goal is to encompass, in a self-consistent scheme, problems like Inflation, Dark Energy, Dark Matter, Large Scale Structure and, first of all, to give at least an effective description of Quantum Gravity. We review the basic principles that any gravitational theory has to follow. The geometrical interpretation is discussed in a broad perspective in order to highlight the basic assumptions of General Relativity and its possible extensions in the general framework of gauge theories. Principles of such modifications are presented, focusing on specific classes of theories like f (R)-gravity and scalar-tensor gravity in the metric and Pala...
Arun, K. G.; Pai, Archana
2013-01-01
Gravitational wave (GW) observations of coalescing compact binaries will be unique probes of strong-field, dynamical aspects of relativistic gravity. We present a short review of various schemes proposed in the literature to test general relativity (GR) and alternative theories of gravity using inspiral waveforms. Broadly these schemes may be classified into two types: model dependent and model independent. In the model dependent category, GW observations are compared against a specific waveform model representative of a particular theory or a class of theories such as scalar-tensor theories, dynamical Chern-Simons theory and massive graviton theories. Model independent tests are attempts to write down a parametrized gravitational waveform where the free parameters take different values for different theories and (at least some of) which can be constrained by GW observations. We revisit some of the proposed bounds in the case of downscaled LISA configuration (eLISA) and compare them with the original LISA configuration. We also compare the expected bounds on alternative theories of gravity from ground-based and space-based detectors and find that space-based GW detectors can test GR and other theories of gravity with unprecedented accuracies. We then focus on a recent proposal to use singular value decomposition of the Fisher information matrix to improve the accuracies with which post-Newtonian theory can be tested. We extend those results to the case of space-based detector eLISA and discuss its implications.
Arun, K G
2013-01-01
Gravitational Wave (GW) observations of coalescing compact binaries will be unique probes of strong-field, dynamical aspects of relativistic gravity. We present a short review of various schemes proposed in the literature to test General Relativity (GR) and alternative theories of gravity using inspiral waveforms. Broadly these schemes may be classified into two types: model dependent and model independent. In the model dependent category, GW observations are compared against a specific waveform model representative of a particular theory or a class of theories like Scalar-Tensor theories, Dynamical Chern-Simons theory and Massive graviton theories. Model independent tests are attempts to write down a parametrised gravitational waveform where the free parameters take different values for different theories and (at least some of) which can be constrained by GW observations. We revisit some of the proposed bounds in the case of downscaled LISA configuration (eLISA) and compare them with the original LISA config...
Davydov, E A
2013-01-01
Nowadays it is widely accepted that the evolution of the universe was driven by some scalar degrees of freedom both on its early stage and at present. The corresponding cosmological models often involve some scalar fields introduced ad hoc. In this paper we cultivate a different approach, which is based on a derivation of new scalar degrees of freedom from fundamental modifications of Einstein's gravity. In elaboration of our previous work, we here investigate properties of the dilaton-scalar gravity obtained by dimensional reductions of a recently proposed affine generalized gravity theory. We show that these models possess the same symmetries as related models of GR with ordinary scalar fields. As a result, for a rather general class of dilaton-scalar gravity models we construct additional first integrals and formulate an integral equation well suited for solving by iterations.
Stationary Black Holes in a Generalized Three-Dimensional Theory of Gravity
Sá, P M
1998-01-01
We consider a generalized three-dimensional theory of gravity which is specified by two fields, the graviton and the dilaton, and one parameter. This theory contains, as particular cases, three-dimensional General Relativity and three-dimensional String Theory. Stationary black hole solutions are generated from the static ones using a simple coordinate transformation. The stationary black holes solutions thus obtained are locally equivalent to the corresponding static ones, but globally distinct. The mass and angular momentum of the stationary black hole solutions are computed using an extension of the Regge and Teitelboim formalism. The causal structure of the black holes is described.
Mass bounds for compact spherically symmetric objects in generalized gravity theories
Burikham, Piyabut; Lake, Matthew J
2016-01-01
We derive upper and lower bounds on the mass-radius ratio of stable compact objects in extended gravity theories, in which modifications of the gravitational dynamics via-{\\' a}-vis standard general relativity are described by an effective contribution to the matter energy-momentum tensor. Our results include the possibility of a variable coupling between the matter sector and the gravitational field and are valid for a large class of generalized gravity models. The generalized continuity and Tolman-Oppenheimer-Volkoff equations are expressed in terms of the effective mass, density and pressure, given by the bare values plus additional contributions from the total energy-momentum tensor, and general theoretical limits for the maximum and minimum mass-radius ratios are explicitly obtained. As an applications of the formalism developed herein, we consider compact bosonic objects, described by scalar-tensor gravitational theories with self-interacting scalar field potentials, and charged compact objects, respect...
Generalizing unimodular gravity
Saez-Gomez, Diego
2016-01-01
The so-called unimodular version of General Relativity is revisited, which assumes the trace-free part of the equations instead of the usual Einstein equations, what leads naturally to a cosmological constant that may compensate the large value of quantum fluctuations. Here we extend such formalism to some extensions of General Relativity that have drawn a lot of attention over the last years, as $f(R)$ gravity (or its equivalent scalar-tensor picture) and Gauss-Bonnet gravity. The corresponding unimodular version of such theories is constructed. From the classical point of view, the unimodular versions of such extensions are completely equivalent to their originals, but an effective cosmological constant arises naturally, what may provide a richer description of the universe evolution. Moreover, conformal transformations within unimodular gravities lead to some corrections that may affect their solutions. Here we analyze the case of Starobisnky inflation and compared with the original one.
Mass bounds for compact spherically symmetric objects in generalized gravity theories
Burikham, Piyabut; Harko, Tiberiu; Lake, Matthew J.
2016-09-01
We derive upper and lower bounds on the mass-radius ratio of stable compact objects in extended gravity theories, in which modifications of the gravitational dynamics via-á-vis standard general relativity are described by an effective contribution to the matter energy-momentum tensor. Our results include the possibility of a variable coupling between the matter sector and the gravitational field and are valid for a large class of generalized gravity models. The generalized continuity and Tolman-Oppenheimer-Volkoff equations are expressed in terms of the effective mass, density, and pressure, given by the bare values plus additional contributions from the total energy-momentum tensor, and general theoretical limits for the maximum and minimum mass-radius ratios are explicitly obtained. As applications of the formalism developed herein, we consider compact bosonic objects, described by scalar-tensor gravitational theories with self-interacting scalar field potentials, and charged compact objects, respectively. For Higgs-type models, we find that these bounds can be expressed in terms of the value of the potential at the surface of the compact object. Minimizing the energy with respect to the radius, we obtain explicit upper and lower bounds on the mass, which admits a Chandrasekhar-type representation. For charged compact objects, we consider the effects of the Poincaré stresses on the equilibrium structure and obtain bounds on the radial and tangential stresses. As a possible astrophysical test of our results, we obtain the general bound on the gravitational redshift for compact objects in extended gravity theories and explicitly compute the redshift restrictions for objects with nonzero effective surface pressure. General implications of minimum mass bounds for the gravitational stability of fundamental particles and for the existence of holographic duality between bulk and boundary degrees of freedom are also considered.
Post-relativistic gravity a hidden variable theory for general relativity
Schmelzer, I
1996-01-01
Post-relativistic gravity is a hidden variable theory for general relativity. It introduces the pre-relativistic notions absolute space, absolute time, and ether as hidden variables into general relativity. Evolution is defined by the equations of general relativity and the harmonic coordinate condition interpreted as a physical equation. There are minor differences in predictions compared with general relativity (i.e. trivial topology of the universe is predicted). The unobservable absolute time is designed to solve the problem of time in quantization of general relativity. Background space and time define a Newtonian frame for the quantization of the gravitational field. By the way, a lot of other conceptual problems of quantization will be solved (i.e. no constraints, no topological foam, no black hole and bib bang singularities, natural vacuum definition for quantum fields on classical background).
Geometric scalar theory of gravity
Energy Technology Data Exchange (ETDEWEB)
Novello, M.; Bittencourt, E.; Goulart, E.; Salim, J.M.; Toniato, J.D. [Instituto de Cosmologia Relatividade Astrofisica ICRA - CBPF Rua Dr. Xavier Sigaud 150 - 22290-180 Rio de Janeiro - Brazil (Brazil); Moschella, U., E-mail: novello@cbpf.br, E-mail: eduhsb@cbpf.br, E-mail: Ugo.Moschella@uninsubria.it, E-mail: egoulart@cbpf.br, E-mail: jsalim@cbpf.br, E-mail: toniato@cbpf.br [Università degli Studi dell' Insubria - Dipartamento di Fisica e Matematica Via Valleggio 11 - 22100 Como - Italy (Italy)
2013-06-01
We present a geometric scalar theory of gravity. Our proposal will be described using the ''background field method'' introduced by Gupta, Feynman, Deser and others as a field theory formulation of general relativity. We analyze previous criticisms against scalar gravity and show how the present proposal avoids these difficulties. This concerns not only the theoretical complaints but also those related to observations. In particular, we show that the widespread belief of the conjecture that the source of scalar gravity must be the trace of the energy-momentum tensor — which is one of the main difficulties to couple gravity with electromagnetic phenomenon in previous models — does not apply to our geometric scalar theory. From the very beginning this is not a special relativistic scalar gravity. The adjective ''geometric'' pinpoints its similarity with general relativity: this is a metric theory of gravity. Some consequences of this new scalar theory are explored.
On the motion of rotating bodies in field gravity theory and general relativity
Baryshev, Yu V
2000-01-01
On the basis of Lagrangian formalism of relativistic field theory post-Newtonian equations of motion for a rotating body are derived in the frame of Feynman's quantum field gravity theory (FGT) and compared with corresponding geodesic equations in general relativity (GR). It is shown that in FGT the trajectory of a rotating test body does not depend on a choice of a coordinate system. The equation of translational motion of a gyroscope is applied to description of laboratory experiments with free falling rotating bodies and rotating bodies on a balance scale. Post-Newtonian relativistic effect of periodical modulation of the orbital motion of a rotating body is discussed for the case of planets of the solar system and for binary pulsars PSR B1913+16 and PSR B1259-63. In the case of binary pulsars with known spin orientations this effect gives a possibility to measure radiuses of neutron stars.
Energy-Momentum of the Friedmann Models in General Relativity and Teleparallel Theory of Gravity
Sharif, M
2008-01-01
This paper is devoted to the evaluation of the energy-momentum density components for the Friedmann models. For this purpose, we have used M${\\o}$ller's pseudotensor prescription in General Relativity and a certain energy-momentum density developed from his teleparallel formulation. It is shown that the energy density of the closed Friedmann universe vanishes on the spherical shell at the radius $\\rho=2\\sqrt{3}$. This coincides with the earlier results available in the literature. We also discuss the energy of the flat and open models. A comparison shows a partial consistency between the M${\\o}$ller's pseudotensor for General Relativity and teleparallel theory. Further, it is shown that the results are independent of the free dimensionless coupling constant of the teleparallel gravity.
Radioscience simulations in General Relativity and in alternative theories of gravity
Hees, Aurelien; Lamine, Brahim; Reynaud, Serge; Jaekel, Marc-Thierry; Poncin-Lafitte, Christophe Le; Lainey, Valery; Fuzfa, Andre; Dehant, Veronique
2011-01-01
In this communication, we focus on the possibility to test GR with radioscience experiments. We present a new software that in a first step simulates the Range/Doppler signals directly from the space time metric (thus in GR and in alternative theories of gravity). In a second step, a least-squares fit of the involved parameters is performed in GR. This software allows one to get the order of magnitude and the signature of the modifications induced by an alternative theory of gravity on radioscience signals. As examples, we present some simulations for the Cassini mission in Post-Einsteinian gravity and with the MOND External Field Effect.
Cosmological structures in generalized gravity
Hwang, J
1997-01-01
In a class of generalized gravity theories with general couplings between the scalar field and the scalar curvature in the Lagrangian, we describe the quantum generation and the classical evolution processes of both the scalar and tensor structures in a simple and unified manner.
Kan, Nahomi; Maki, Takuya; Shiraishi, Kiyoshi
2016-10-01
We propose a model of gravity in which a General Relativity metric tensor and an effective metric generated from a single scalar formulated in geometric scalar gravity are mixed. We show that the model yields the exact Schwarzschild solution, along with accelerating behavior of scale factors in cosmological solutions.
Othman, Mohamed I. A.; Elmaklizi, Yassmin D.; Said, Samia M.
2013-03-01
The problem of the generalized thermoelastic medium for three different theories under the effect of a gravity field is investigated. The Lord-Shulman (L-S), Green-Lindsay (G-L), and classical-coupled (CD) theories are discussed. The modulus of the elasticity is given as a linear function of the reference temperature. The exact expressions for the displacement components, temperature, and stress components are obtained by using normal mode analysis. Numerical results for the field quantities are given in the physical domain and illustrated graphically in the absence and presence of gravity. A comparison also is made between the three theories for the results with and without a temperature dependence.
Mitra, Saugata; Chakraborty, Subenoy
2016-01-01
The present work deals with a detailed study of universal thermodynamics in different modified gravity theories. The validity of the generalized second law of thermodynamics (GSLT) and thermodynamical equilibrium (TE) of the Universe bounded by a horizon (apparent/event) in f(R)-gravity, Einstein-Gauss-Bonnet gravity, RS-II brane scenario and DGP brane model has been investigated. In the perspective of recent observational evidences, the matter in the Universe is chosen as interacting holographic dark energy model. The entropy on the horizons are evaluated from the validity of the unified first law and as a result there is a correction (in integral form) to the usual Bekenstein entropy. The other thermodynamical parameter namely temperature on the horizon is chosen as the recently introduced corrected Hawking temperature. The above thermodynamical analysis is done for homogeneous and isotropic flat FLRW model of the Universe. The restrictions for the validity of GSLT and the TE are presented in tabular form f...
Alternative theories of gravity and Lorentz violation
Xu, Rui; Foster, Joshua; Kostelecky, V. Alan
2017-01-01
General relativity has achieved many successes, including the prediction of experimental results. However, its incompatibility with quantum theory remains an obstacle. By extending the foundational properties of general relativity, alternative theories of gravity can be constructed. In this talk, we focus on fermion couplings in the weak-gravity limit of certain alternative theories of gravity. Under suitable experimental circumstances, some of these couplings match terms appearing in the gravitational SME, which is a general framework describing violations of local Lorentz invariance. Existing limits on Lorentz violation can therefore be used to constrain certain Lorentz-invariant alternative theories of gravity.
Inflationary spectra in generalized gravity Unified forms
Noh, H
2001-01-01
The classical evolution and the quantum generation processes of the scalar- and tensor-type cosmological perturbations in the context of a broad class of generalized gravity theories are presented in unified forms. The exact forms of final spectra of the two types of structures generated during a generalized slow-roll inflation are derived. Results in generalized gravity are characterized by two additional parameters which are the coupling between gravity and field, and the nonminimal coupling in the kinetic part of the field. Our general results include widely studied gravity theories and inflation models as special cases, and show how the well known consistency relation and spectra in ordinary Einstein gravity inflation models are affected by the generalized nature of the gravity theories.
Bondarescu, Ruxandra; Jetzer, Philippe; Angélil, Raymond; Saha, Prasenjit; Lundgren, Andrew
2015-01-01
The successful miniaturisation of extremely accurate atomic clocks and atom interferometers invites prospects for satellite missions to perform precision experiments. We discuss the effects predicted by general relativity and alternative theories of gravity that can be detected by a clock, which orbits the Earth. Our experiment relies on the precise tracking of the spacecraft using its observed tick-rate. The spacecraft's reconstructed four-dimensional trajectory will reveal the nature of gravitational perturbations in Earth's gravitational field, potentially differentiating between different theories of gravity. This mission can measure multiple relativistic effects all during the course of a single experiment, and constrain the Parametrized Post-Newtonian Parameters around the Earth. A satellite carrying a clock of fractional timing inaccuracy of $\\Delta f/f \\sim 10^{-16}$ in an elliptic orbit around the Earth would constrain the PPN parameters $|\\beta -1|, |\\gamma-1| \\lesssim 10^{-6}$. We also briefly revi...
Nonassociative gravity in string theory?
Energy Technology Data Exchange (ETDEWEB)
Blumenhagen, R [Max-Planck-Institut fuer Physik (Werner-Heisenberg-Institut), Foehringer Ring 6, 80805 Muenchen (Germany); Plauschinn, E, E-mail: ralph.blumenhagen@mpp.mpg.d, E-mail: e.plauschinn@uu.n [Institute for Theoretical Physics and Spinoza Institute, Utrecht University, 3508 TD Utrecht (Netherlands)
2011-01-07
In an on-shell conformal field theory approach, we find indications of a three-bracket structure for target space coordinates in general closed string backgrounds. This generalizes the appearance of noncommutative gauge theories for open strings in two-form backgrounds to a putative noncommutative/nonassociative gravity theory for closed strings probing curved backgrounds with non-vanishing three-form flux. Several aspects and consequences of the three-bracket structure are discussed and a new type of generalized uncertainty principle is proposed.
Lovelock gravities from Born–Infeld gravity theory
Directory of Open Access Journals (Sweden)
P.K. Concha
2017-02-01
Full Text Available We present a Born–Infeld gravity theory based on generalizations of Maxwell symmetries denoted as Cm. We analyze different configuration limits allowing to recover diverse Lovelock gravity actions in six dimensions. Further, the generalization to higher even dimensions is also considered.
Brustein, Ram; Hadad, Merav
2009-09-04
We show that the equations of motion of generalized theories of gravity are equivalent to the thermodynamic relation deltaQ=TdeltaS. Our proof relies on extending previous arguments by using a more general definition of the Noether charge entropy. We have thus completed the implementation of Jacobson's proposal to express Einstein's equations as a thermodynamic equation of state. Additionally, we find that the Noether charge entropy obeys the second law of thermodynamics if the energy-momentum tensor obeys the null energy condition. Our results support the idea that gravitation on a macroscopic scale is a manifestation of the thermodynamics of the vacuum.
Renormalizable Quantum Gauge Theory of Gravity
Institute of Scientific and Technical Information of China (English)
WU Ning
2002-01-01
The quantum gravity is formulated based on the principle of local gauge invariance. The model discussedin this paper has local gravitational gauge symmetry, and gravitational field is represented by gauge field. In the leading-order approximation, it gives out classical Newton's theory of gravity. In the first-order approximation and for vacuum,it gives out Einstein's general theory of relativity. This quantum gauge theory of gravity is a renormalizable quantumtheory.
Gravity: a gauge theory perspective
Nester, James M
2016-01-01
The evolution of a generally covariant theory is under-determined. One hundred years ago such dynamics had never before been considered; its ramifications were perplexing, its future important role for all the fundamental interactions under the name gauge principle could not be foreseen. We recount some history regarding Einstein, Hilbert, Klein and Noether and the novel features of gravitational energy that led to Noether's two theorems. Under-determined evolution is best revealed in the Hamiltonian formulation. We developed a covariant Hamiltonian formulation. The Hamiltonian boundary term gives covariant expressions for the quasi-local energy, momentum and angular momentum. Gravity can be considered as a gauge theory of the local Poincar\\'e group. The dynamical potentials of the Poincar\\'e gauge theory of gravity are the frame and the connection. The spacetime geometry has in general both curvature and torsion. Torsion naturally couples to spin; it could have a significant magnitude and yet not be noticed,...
Ezquiaga, Jose María; Zumalacárregui, Miguel
2016-01-01
We use a description based on differential forms to systematically explore the space of scalar-tensor theories of gravity. Within this formalism, we propose a basis for the scalar sector at the lowest order in derivatives of the field and in any number of dimensions. This minimal basis is used to construct a finite and closed set of Lagrangians describing general scalar-tensor theories invariant under Local Lorentz Transformations in a pseudo-Riemannian manifold, which contains ten physically distinct elements in four spacetime dimensions. Subsequently, we compute their corresponding equations of motion and find which combinations are at most second order in derivatives in four as well as arbitrary number of dimensions. By studying the possible exact forms (total derivatives) and algebraic relations between the basis components, we discover that there are only four Lagrangian combinations producing second order equations, which can be associated with Horndeski's theory. In this process, we identify a new seco...
Battista, Emmanuele; Dell'Agnello, Simone; Esposito, Giampiero; Di Fiore, Luciano; Simo, Jules; Grado, Aniello
2015-09-01
We first analyze the restricted four-body problem consisting of the Earth, the Moon, and the Sun as the primaries and a spacecraft as the planetoid. This scheme allows us to take into account the solar perturbation in the description of the motion of a spacecraft in the vicinity of the stable Earth-Moon libration points L4 and L5 both in the classical regime and in the context of effective field theories of gravity. A vehicle initially placed at L4 or L5 will not remain near the respective points. In particular, in the classical case the vehicle moves on a trajectory about the libration points for at least 700 days before escaping. We show that this is true also if the modified long-distance Newtonian potential of effective gravity is employed. We also evaluate the impulse required to cancel out the perturbing force due to the Sun in order to force the spacecraft to stay precisely at L4 or L5. It turns out that this value is slightly modified with respect to the corresponding Newtonian one. In the second part of the paper, we first evaluate the location of all Lagrangian points in the Earth-Moon system within the framework of general relativity. For the points L4 and L5, the corrections of coordinates are of order a few millimeters and describe a tiny departure from the equilateral triangle. After that, we set up a scheme where the theory which is quantum corrected has as its classical counterpart the Einstein theory, instead of the Newtonian one. In other words, we deal with a theory involving quantum corrections to Einstein gravity, rather than to Newtonian gravity. By virtue of the effective-gravity correction to the long-distance form of the potential among two masses, all terms involving the ratio between the gravitational radius of the primary and its separation from the planetoid get modified. Within this framework, for the Lagrangian points of stable equilibrium, we find quantum corrections of order 2 mm, whereas for Lagrangian points of unstable
Ensemble Averaged Gravity Theory
Khosravi, Nima
2016-01-01
We put forward the idea that all the theoretically consistent models of gravity have a contribution to the observed gravity interaction. In this formulation each model comes with its own Euclidean path integral weight where general relativity (GR) automatically has the maximum weight in high-curvature regions. We employ this idea in the framework of Lovelock models and show that in four dimensions the result is a specific form of $f(R,G)$ model. This specific $f(R,G)$ satisfies the stability conditions and has self-accelerating solution. Our model is consistent with the local tests of gravity since its behavior is same as GR for high-curvature regimes. In low-curvature regime the gravity force is weaker than GR which can interpret as existence of a repulsive fifth force for very large scales. Interestingly there is an intermediate-curvature regime where the gravity force is stronger in our model than GR. The different behavior of our model in comparison with GR in both low- and intermediate-curvature regimes ...
Battista, Emmanuele; Esposito, Giampiero; Di Fiore, Luciano; Simo, Jules; Grado, Aniello
2015-01-01
In the restricted four-body problem consisting of the Earth, the Moon and the Sun as the primaries and a spacecraft as the planetoid, we take into account the solar perturbation in the description of the motion of a spacecraft in the vicinity of the stable Earth-Moon libration points L4 and L5 both in the classical regime and in the context of effective field theories of gravity. We then evaluate the location of all Lagrangian points in the Earth-Moon system within the framework of general relativity. For the points L4 and L5, the corrections of coordinates are of order a few millimeters. After that, we set up a scheme where the theory which is quantum corrected has as its classical counterpart the Einstein theory, instead of the Newtonian one. By virtue of the effective-gravity correction to the longdistance form of the potential among two point masses, all terms involving the ratio between the gravitational radius of the primary and its separation from the planetoid get modified. Within this framework, for ...
Directory of Open Access Journals (Sweden)
Bondarescu Ruxandra
2015-01-01
Full Text Available The successful miniaturisation of extremely accurate atomic clocks and atom interferometers invites prospects for satellite missions to perform precision experiments. We discuss the effects predicted by general relativity and alternative theories of gravity that can be detected by a clock, which orbits the Earth. Our experiment relies on the precise tracking of the spacecraft using its observed tick-rate. The spacecraft’s reconstructed four-dimensional trajectory will reveal the nature of gravitational perturbations in Earth’s gravitational field, potentially differentiating between different theories of gravity. This mission can measure multiple relativistic effects all during the course of a single experiment, and constrain the Parametrized Post-Newtonian Parameters around the Earth. A satellite carrying a clock of fractional timing inaccuracy of Δ f / f ∼ 10−16 in an elliptic orbit around the Earth would constrain the PPN parameters |β − 1|, |γ − 1| ≲ 10−6. We also briefly review potential constraints by atom interferometers on scalar tensor theories and in particular on Chameleon and dilaton models.
Ezquiaga, Jose María; García-Bellido, Juan; Zumalacárregui, Miguel
2016-07-01
We use a description based on differential forms to systematically explore the space of scalar-tensor theories of gravity. Within this formalism, we propose a basis for the scalar sector at the lowest order in derivatives of the field and in any number of dimensions. This minimal basis is used to construct a finite and closed set of Lagrangians describing general scalar-tensor theories invariant under local Lorentz transformations in a pseudo-Riemannian manifold, which contains ten physically distinct elements in four spacetime dimensions. Subsequently, we compute their corresponding equations of motion and find which combinations are at most second order in derivatives in four as well as an arbitrary number of dimensions. By studying the possible exact forms (total derivatives) and algebraic relations between the basis components, we discover that there are only four Lagrangian combinations producing second-order equations, which can be associated with Horndeski's theory. In this process, we identify a new second-order Lagrangian, named kinetic Gauss-Bonnet, that was not previously considered in the literature. However, we show that its dynamics is already contained in Horndeski's theory. Finally, we provide a full classification of the relations between different second-order theories. This allows us to clarify, for instance, the connection between different covariantizations of Galileons theory. In conclusion, our formulation affords great computational simplicity with a systematic structure. As a first step, we focus on theories with second-order equations of motion. However, this new formalism aims to facilitate advances towards unveiling the most general scalar-tensor theories.
Scalar-Tensor Theory of Gravity and Generalized Second Law of Thermodynamics on the Event Horizon
Mazumder, Nairwita
2010-01-01
In blackhole physics, the second law of thermodynamics is generally valid whether the blackhole is a static or a non-static one. Considering the universe as a thermodynamical system the second law of blackhole dynamics extends to the non-negativity of the sum of the entropy of the matter and the horizon, known as generalized second law of thermodynamics(GSLT). Here, we have assumed the universe to be bounded by the event-horizon or filled with perfect fluid and holographic dark energy in two cases. Thus considering entropy to be an arbitrary function of the area of the event-horizon, we have tried to find the conditions and the restrictions over the scalar field and equation of state for the validity of the GSLT and both in quintessence-era and in phantom-era in scalar tensor theory.
Modifications of Einstein's theory of gravity at large distances
2015-01-01
In the last few years modified gravity theories have been proposed as extensions of Einstein's theory of gravity. Their main motivation is to explain the latest cosmological and astrophysical data on dark energy and dark matter. The study of general relativity at small scales has already produced important results (cf e.g. LNP 863 Quantum Gravity and Quantum Cosmology) while its study at large scales is challenging because recent and upcoming observational results will provide important information on the validity of these modified theories. In this volume, various aspects of modified gravity at large scales will be discussed: high-curvature gravity theories; general scalar-tensor theories; Galileon theories and their cosmological applications; F(R) gravity theories; massive, new massive and topologically massive gravity; Chern-Simons modifications of general relativity (including holographic variants) and higher-spin gravity theories, to name but a few of the most important recent developments. Edite...
Gravity: A gauge theory perspective
Nester, James M.; Chen, Chiang-Mei
2016-07-01
The evolution of a generally covariant theory is under-determined. One hundred years ago such dynamics had never before been considered; its ramifications were perplexing, its future important role for all the fundamental interactions under the name gauge principle could not be foreseen. We recount some history regarding Einstein, Hilbert, Klein and Noether and the novel features of gravitational energy that led to Noether’s two theorems. Under-determined evolution is best revealed in the Hamiltonian formulation. We developed a covariant Hamiltonian formulation. The Hamiltonian boundary term gives covariant expressions for the quasi-local energy, momentum and angular momentum. Gravity can be considered as a gauge theory of the local Poincaré group. The dynamical potentials of the Poincaré gauge theory of gravity are the frame and the connection. The spacetime geometry has in general both curvature and torsion. Torsion naturally couples to spin; it could have a significant magnitude and yet not be noticed, except on a cosmological scale where it could have significant effects.
Severe Challenges In Gravity Theories
Ha, Yuan K
2011-01-01
Gravity is specifically the attractive force between two masses separated at a distance. Is this force a derived or a fundamental interaction? We believe that all fundamental interactions are quantum in nature but a derived interaction may be classical. Severe challenges have appeared in many quantum theories of gravity. None of these theories has thus far attained its goal in quantizing gravity and some have met remarkable defeat. We are led to ponder whether gravitation is intrinsically classical and that there would exist a deeper and structurally different underlying theory which would give rise to classical gravitation, in the sense that statistical mechanics, quantum or classical, provides the underlying theory of classical thermodynamics.
Stochastic Gravity: Theory and Applications
Directory of Open Access Journals (Sweden)
Hu Bei Lok
2004-01-01
Full Text Available Whereas semiclassical gravity is based on the semiclassical Einstein equation with sources given by the expectation value of the stress-energy tensor of quantum fields, stochastic semiclassical gravity is based on the Einstein-Langevin equation, which has in addition sources due to the noise kernel. The noise kernel is the vacuum expectation value of the (operator-valued stress-energy bi-tensor which describes the fluctuations of quantum matter fields in curved spacetimes. In the first part, we describe the fundamentals of this new theory via two approaches: the axiomatic and the functional. The axiomatic approach is useful to see the structure of the theory from the framework of semiclassical gravity, showing the link from the mean value of the stress-energy tensor to their correlation functions. The functional approach uses the Feynman-Vernon influence functional and the Schwinger-Keldysh closed-time-path effective action methods which are convenient for computations. It also brings out the open systems concepts and the statistical and stochastic contents of the theory such as dissipation, fluctuations, noise, and decoherence. We then focus on the properties of the stress-energy bi-tensor. We obtain a general expression for the noise kernel of a quantum field defined at two distinct points in an arbitrary curved spacetime as products of covariant derivatives of the quantum field's Green function. In the second part, we describe three applications of stochastic gravity theory. First, we consider metric perturbations in a Minkowski spacetime. We offer an analytical solution of the Einstein-Langevin equation and compute the two-point correlation functions for the linearized Einstein tensor and for the metric perturbations. Second, we discuss structure formation from the stochastic gravity viewpoint, which can go beyond the standard treatment by incorporating the full quantum effect of the inflaton fluctuations. Third, we discuss the backreaction
Generalized modified gravity in large extra dimensions
Energy Technology Data Exchange (ETDEWEB)
Aslan, Onder [Department of Physics, Izmir Institute of Technology, IZTECH, TR-35430 Izmir (Turkey); Demir, Durmus A. [Department of Physics, Izmir Institute of Technology, IZTECH, TR-35430 Izmir (Turkey)]. E-mail: demir@physics.iztech.edu.tr
2006-04-20
We discuss effective interactions among brane matter induced by modifications of higher-dimensional Einstein gravity through the replacement of Einstein-Hilbert term with a generic function f(R,R{sub AB}R{sup AB},R{sub ABCD}R{sup ABCD}) of the curvature tensors. We determine gravi-particle spectrum of the theory, and perform a comparative analysis of its predictions with those of the Einstein gravity within Arkani-Hamed-Dvali-Dimopoulos (ADD) setup. We find that this general higher-curvature quantum gravity theory contributes to scatterings among both massive and massless brane matter (in contrast to much simpler generalization of the Einstein gravity, f(R), which influences only the massive matter), and therefore, can be probed via various scattering processes at present and future colliders and directly confronted with the ADD expectations. In addition to collision processes which proceed with tree-level gravi-particle exchange, effective interactions among brane matter are found to exhibit a strong sensitivity to higher-curvature gravity via the gravi-particle loops. Furthermore, particle collisions with missing energy in their final states are found to be sensitive to additional gravi-particles not found in Einstein gravity. In general, road to a correct description of quantum gravity above Fermi energies depends crucially on if collider and other search methods end up with a negative or positive answer for the presence of higher-curvature gravitational interactions.
f(Lovelock) theories of gravity
Bueno, Pablo; A., Oscar Lasso; Ramirez, Pedro F
2016-01-01
f(Lovelock) gravities are simple generalizations of the usual f(R) and Lovelock theories in which the gravitational action depends on some arbitrary function of the corresponding dimensionally-extended Euler densities. In this paper we study several aspects of these theories in general dimensions. We start by identifying the generalized boundary term which makes the gravitational variational problem well-posed. Then, we show that these theories are equivalent to certain scalar-tensor theories and how this relation is characterized by the Hessian of f. We also study the linearized equations of the theory on general maximally symmetric backgrounds. Remarkably, we find that these theories do not propagate the usual ghost-like massive gravitons characteristic of higher-derivative gravities on such backgrounds. In some non-trivial cases, the additional scalar associated to the trace of the metric perturbation is also absent, being the usual graviton the only dynamical field. In those cases, the linearized equation...
Unimodular Theory of Gravity and Inflation
Cho, Inyong
2014-01-01
We study inflation and its scalar perturbations in the unimodular theory of gravity. When the unimodular parameter is $\\xi=6$, the classical picture of inflation such as the slow-roll parameters, the number of $e$-foldings and the scale of the scalar field, can be reproduced in the unimodular theory because it recovers the background equations of the standard theory of general relativity. Considering the scalar perturbation, the unimodular gravity constrains the gauge degree of freedom, but the perturbation equations are similar to those in general relativity. For $\\xi \
Observational Constraints on Transverse Gravity: a Generalization of Unimodular Gravity
Lopez-Villarejo, J J
2010-01-01
We explore the hypothesis that the set of symmetries enjoyed by the theory that describes gravity is not the full group of diffeomorphisms Diff(M), as in General Relativity, but a maximal subgroup of it, TransverseDiff(M), with its elements having a jacobian equal to unity; at the infinitesimal level, the parameter describing the coordinate change, xi^mu (x), is transverse, i.e., partial_mu(xi^mu)=0. Incidentally, this is the smaller symmetry one needs to propagate consistently a graviton, which is a great theoretical motivation for considering these theories. Also, the determinant of the metric, g, behaves as a "transverse scalar", so that these theories can be seen as a generalization of the better-known unimodular gravity. We present our results on the observational constraints on transverse gravity, in close relation with the claim of equivalence with general scalar-tensor theory. We also comment on the structure of the divergences of the quantum theory to the one-loop order.
Quantum gravity from theory to experimental search
Kiefer, Claus; Lämmerzahl, Claus
2003-01-01
The relation between quantum theory and the theory of gravitation remains one of the most outstanding unresolved issues of modern physics. According to general expectation, general relativity as well as quantum (field) theory in a fixed background spacetime cannot be fundamentally correct. Hence there should exist a broader theory comprising both in appropriate limits, i.e., quantum gravity. This book gives readers a comprehensive introduction accessible to interested non-experts to the main issues surrounding the search for quantum gravity. These issues relate to fundamental questions concerning the various formalisms of quantization; specific questions concerning concrete processes, like gravitational collapse or black-hole evaporation; and the all important question concerning the possibility of experimental tests of quantum-gravity effects.
Testing Gravity Theories Using Stars
Sakstein, Jeremy; Vikram, Vinu
2014-01-01
Modified theories of gravity have received a renewed interest due to their ability to account for the cosmic acceleration. In order to satisfy the solar system tests of gravity, these theories need to include a screening mechanism that hides the modifications on small scales. One popular and well-studied theory is chameleon gravity. Our own galaxy is necessarily screened, but less dense dwarf galaxies may be unscreened and their constituent stars can exhibit novel features. In particular, unscreened stars are brighter, hotter and more ephemeral than screened stars in our own galaxy. They also pulsate with a shorter period. In this essay, we exploit these new features to constrain chameleon gravity to levels three orders of magnitude lower the previous measurements. These constraints are currently the strongest in the literature.
Geometric Formulation of Gauge Theory of Gravity
Institute of Scientific and Technical Information of China (English)
WUNing; ZHANGDa-Hua; RUANTu-Nan
2003-01-01
DitTerential geometric formulation of quantum gauge theory of gravity is studied in this paper. The quantum gauge theory of gravity is formulated completely in the framework of traditional quantum field theory. In order to study the relationship between quantum gauge theory of gravity and traditional quantum gravity which is formulated in curved space, it is important to set up the geometry picture of quantum gauge theory of gravity. The correspondence between quantum gauge theory of gravity and differential geometry is discussed and the geometry picture of quantum gauge theory of gravity is studied.
Aspects of general higher-order gravities
Bueno, Pablo; Min, Vincent S; Visser, Manus R
2016-01-01
We study several aspects of higher-order gravities constructed from general contractions of the Riemann tensor and the metric in arbitrary dimensions. First, we use the fast-linearization procedure presented in arXiv:1607.06463 to obtain the equations satisfied by the metric perturbation modes on a maximally symmetric background in the presence of matter and to classify $\\mathcal{L}($Riemann$)$ theories according to their spectrum. Then, we linearize all theories up to quartic order in curvature and use this result to construct quartic versions of Einsteinian cubic gravity (ECG). In addition, we show that the most general cubic gravity constructed in a dimension-independent way and which does not propagate the ghost-like spin-2 mode (but can propagate the scalar) is a linear combination of $f($Lovelock$)$ invariants, plus the ECG term, plus a New ghost-free gravity term. Next, we construct the generalized Newton potential and the Post-Newtonian parameter $\\gamma$ for general $\\mathcal{L}($Riemann$)$ gravities...
Geometric Formulation of Gauge Theory of Gravity
Institute of Scientific and Technical Information of China (English)
WU Ning; ZHANG Da-Hua; RUAN Tu-Nan
2003-01-01
Differential geometric formulation of quantum gauge theory of gravity is studied in this paper. The quantumgauge theory of gravity is formulated completely in the framework of traditional quantum field theory. In order to studythe relationship between quantum gauge theory of gravity and traditional quantum gravity which is formulated in curvedspace, it is important to set up the geometry picture of quantum gauge theory of gravity. The correspondence betweenquantum gauge theory of gravity and differential geometry is discussed and the geometry picture of quantum gaugetheory of gravity is studied.
Stochastic Gravity: Theory and Applications
Directory of Open Access Journals (Sweden)
Hu Bei Lok
2008-05-01
Full Text Available Whereas semiclassical gravity is based on the semiclassical Einstein equation with sources given by the expectation value of the stress-energy tensor of quantum fields, stochastic semiclassical gravity is based on the Einstein–Langevin equation, which has, in addition, sources due to the noise kernel. The noise kernel is the vacuum expectation value of the (operator-valued stress-energy bitensor, which describes the fluctuations of quantum-matter fields in curved spacetimes. A new improved criterion for the validity of semiclassical gravity may also be formulated from the viewpoint of this theory. In the first part of this review we describe the fundamentals of this new theory via two approaches: the axiomatic and the functional. The axiomatic approach is useful to see the structure of the theory from the framework of semiclassical gravity, showing the link from the mean value of the stress-energy tensor to the correlation functions. The functional approach uses the Feynman–Vernon influence functional and the Schwinger–Keldysh closed-time-path effective action methods. In the second part, we describe three applications of stochastic gravity. First, we consider metric perturbations in a Minkowski spacetime, compute the two-point correlation functions of these perturbations and prove that Minkowski spacetime is a stable solution of semiclassical gravity. Second, we discuss structure formation from the stochastic-gravity viewpoint, which can go beyond the standard treatment by incorporating the full quantum effect of the inflaton fluctuations. Third, using the Einstein–Langevin equation, we discuss the backreaction of Hawking radiation and the behavior of metric fluctuations for both the quasi-equilibrium condition of a black-hole in a box and the fully nonequilibrium condition of an evaporating black hole spacetime. Finally, we briefly discuss the theoretical structure of stochastic gravity in relation to quantum gravity and point out
Noncommutative Topological Theories of Gravity
García-Compéan, H; Ramírez, C; Sabido, M
2003-01-01
The possibility of noncommutative gravity arising in the same manner as Yang-Mills theory is explored. Using the Seiberg-Witten map we give a noncommutative version of topological gravity, from which the Euler characteristic and the signature are obtained, in both cases up to third order in the noncommutativity parameter. Finally, we discuss possible ways towards obtaining noncommutative gravitational instantons and to detect local and global gravitational anomalies within this context.
Gravity theory through affine spheres
Minguzzi, E.
2017-08-01
In this work it is argued that in order to improve our understanding of gravity and spacetime our most successful theory, general relativity, must be destructured. That is, some geometrical assumptions must be dropped and recovered just under suitable limits. Along this line of thought we pursue the idea that the roundness of the light cone, and hence the isotropy of the speed of light, must be relaxed and that, in fact, the shape of light cones must be regarded as a dynamical variable. Mathematically, we apply some important results from affine differential geometry to this problem, the idea being that in the transition we should preserve the identification of the spacetime continuum with a manifold endowed with a cone structure and a spacetime volume form. To that end it is suggested that the cotangent indicatrix (dispersion relation) must be described by an equation of Monge-Ampère type determining a hyperbolic affine sphere, at least whenever the matter content is negligible. Non-relativistic spacetimes fall into this description as they are recovered whenever the center of the affine sphere is at infinity. In the more general context of Lorentz-Finsler theories it is shown that the lightlike unparametrized geodesic flow is completely determined by the distribution of light cones. Moreover, the transport of lightlike momenta is well defined though there could be no notion of affine parameter. Finally, we show how the perturbed indicatrix can be obtained from the perturbed light cone.
Asymptotic freedom of Yang-Mills theory with gravity
Folkerts, Sarah; Pawlowski, Jan M
2011-01-01
We study the high energy behaviour of Yang-Mills theory under the inclusion of gravity. In the weak-gravity limit, the running gauge coupling receives no contribution from the gravitational sector, if all symmetries are preserved. This holds true with and without cosmological constant. We also show that asymptotic freedom persists in general field-theory-based gravity scenarios including gravitational shielding as well as asymptotically safe gravity.
Asymptotic freedom of Yang-Mills theory with gravity
Energy Technology Data Exchange (ETDEWEB)
Folkerts, Sarah, E-mail: Sarah.Folkerts@physik.uni-muenchen.de [Institut f. Theoretische Physik, Universitaet Heidelberg, Philosophenweg 16, 69120 Heidelberg (Germany); Litim, Daniel F. [Department of Physics and Astronomy, University of Sussex, Brighton, BN1 9QH (United Kingdom); Pawlowski, Jan M. [Institut f. Theoretische Physik, Universitaet Heidelberg, Philosophenweg 16, 69120 Heidelberg (Germany); ExtreMe Matter Inst. EMMI, GSI, Planckstr. 1, 64291 Darmstadt (Germany)
2012-03-19
We study the behaviour of Yang-Mills theory under the inclusion of gravity. In the weak-gravity limit, the running gauge coupling receives no contribution from the gravitational sector, if all symmetries are preserved. This holds true with and without cosmological constant. We also show that asymptotic freedom persists in general field-theory-based gravity scenarios including gravitational shielding as well as asymptotically safe gravity.
Minimal theory of massive gravity
De Felice, Antonio
2016-01-01
We propose a new theory of massive gravity with only two propagating degrees of freedom. After defining the theory in the unitary gauge in the vielbein language, we shall perform a Hamiltonian analysis to count the number of physical degrees of freedom, and then study some phenomenologies. While the homogeneous and isotropic background cosmology and the tensor linear perturbations around it are described by exactly the same equations as those in the de Rham - Gabadadze - Tolley (dRGT) massive gravity, the scalar and vector gravitational degrees of freedom are absent in the new theory at the fully nonlinear level. Hence the new theory provides a stable nonlinear completion of the self-accelerating cosmological solution that was originally found in the dRGT theory.
Loop quantum gravity as an effective theory
Bojowald, Martin
2012-01-01
As a canonical and generally covariant gauge theory, loop quantum gravity requires special techniques to derive effective actions or equations. If the proper constructions are taken into account, the theory, in spite of considerable ambiguities at the dynamical level, allows for a meaningful phenomenology to be developed, by which it becomes falsifiable. The tradiational problems plaguing canonical quantum-gravity theories, such as the anomaly issue or the problem of time, can be overcome or are irrelevant at the effective level, resulting in consistent means of physical evaluations. This contribution presents aspects of canonical equations and related notions of (deformed) space-time structures and discusses implications in loop quantum gravity, such as signature change at high density from holonomy corrections, and falsifiability thanks to inverse-triad corrections.
Finding Horndeski theories with Einstein gravity limits
McManus, Ryan; Peñarrubia, Jorge
2016-01-01
The Horndeski action is the most general scalar-tensor theory with at most second-order derivatives in the equations of motion, thus evading Ostrogradsky instabilities and making it of interest when modifying gravity at large scales. To pass local tests of gravity, these modifications predominantly rely on nonlinear screening mechanisms that recover Einstein's Theory of General Relativity in regions of high density. We derive a set of conditions on the four free functions of the Horndeski action that examine whether a specific model embedded in the action possesses an Einstein gravity limit or not. For this purpose, we develop a new and surprisingly simple scaling method that identifies dominant terms in the equations of motion by considering formal limits of the couplings that enter through the new terms in the modified action. This enables us to find regimes where nonlinear terms dominate and Einstein's field equations are recovered to leading order. Together with an efficient approximation of the scalar fi...
Quantum gravity, effective fields and string theory
Bjerrum-Bohr, N E J
2004-01-01
We look at the various aspects of treating general relativity as a quantum theory. It is briefly studied how to consistently quantize general relativity as an effective field theory. A key achievement here is the long-range low-energy leading quantum corrections to both the Schwarzschild and Kerr metrics. The leading quantum corrections to the pure gravitational potential between two sources are also calculated, both in the mixed theory of scalar QED and quantum gravity and in the pure gravitational theory. The (Kawai-Lewellen-Tye) string theory gauge/gravity relations is next dealt with. We investigate if the KLT-operator mapping extends to the case of higher derivative effective operators. The KLT-relations are generalized, taking the effective field theory viewpoint, and remarkable tree-level amplitude relations between the field theory operators are derived. Quantum gravity is finally looked at from the the perspective of taking the limit of infinitely many spatial dimensions. It is verified that only a c...
Localized gravity in string theory.
Karch, A; Randall, L
2001-08-06
We propose a string realization of the AdS4 brane in AdS5 that is known to localize gravity. Our theory is M D5 branes in the near horizon geometry of N D3 branes, where M and N are appropriately tuned.
Beyond generalized Proca theories
Heisenberg, Lavinia; Tsujikawa, Shinji
2016-01-01
We consider higher-order derivative interactions beyond second-order generalized Proca theories that propagate only the three desired polarizations of a massive vector field besides the two tensor polarizations from gravity. These new interactions follow the similar construction criteria to those arising in the extension of scalar-tensor Horndeski theories to Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories. On the maximally symmetric space-time, we perform the Hessian and Hamiltonian analysis and show the presence of a second-class constraint that removes the would-be ghost associated with the temporal component of the vector field. Furthermore, we study the behavior of linear perturbations on top of the homogeneous and isotropic cosmological background in the presence of a matter perfect fluid and find the same number of propagating degrees of freedom as in generalized Proca theories. Moreover, we obtain the conditions for the avoidance of ghosts and Laplacian instabilities of tensor, vector, and scalar per...
Casimir effect in Extended Theories of Gravity
Lambiase, G; Stabile, An
2016-01-01
We study the Casimir vacuum energy density and the Casimir pressure for a massless scalar field confined between two nearby parallel plates in a slightly curved, static spacetime background, employing the weak field approximation in the framework of Extended Theories of Gravity (ETG). Following a perturbative approach upto second order, we find the gravity correction in the ETG to Casimir vacuum energy density and pressure. The corrections to the vacuum energy density in presence of curved spacetime in the framework of General Relativity (GR) are small and today they are still undetected with the current technology. However, future sensitivity improvement in gravitational interferometer experiments will give an useful tool to detect such effect induced by gravity. For these reason we retain interesting from a theoretical point of view generalize the outcomes of GR in the context of ETG. Finally, we find the general relation to constraining the free parameters of the ETG.
Generalized Parametrization Dependence in Quantum Gravity
Gies, Holger; Lippoldt, Stefan
2015-01-01
We critically examine the gauge, and field-parametrization dependence of renormalization group flows in the vicinity of non-Gau\\ss{}ian fixed points in quantum gravity. While physical observables are independent of such calculational specifications, the construction of quantum gravity field theories typically relies on off-shell quantities such as $\\beta$ functions and generating functionals and thus face potential stability issues with regard to such generalized parametrizations. We analyze a two-parameter class of covariant gauge conditions, the role of momentum-dependent field rescalings and a class of field parametrizations. Using the product of Newton and cosmological constant as an indicator, the principle of minimum sensitivity identifies stationary points in this parametrization space which show a remarkable insensitivity to the parametrization. In the most insensitive cases, the quantized gravity system exhibits a non-Gau\\ss{}ian UV stable fixed point, lending further support to asymptotically free q...
Solving higher curvature gravity theories
Energy Technology Data Exchange (ETDEWEB)
Chakraborty, Sumanta [IUCAA, Pune (India); SenGupta, Soumitra [Indian Association for the Cultivation of Science, Theoretical Physics Department, Kolkata (India)
2016-10-15
Solving field equations in the context of higher curvature gravity theories is a formidable task. However, in many situations, e.g., in the context of f(R) theories, the higher curvature gravity action can be written as an Einstein-Hilbert action plus a scalar field action. We show that not only the action but the field equations derived from the action are also equivalent, provided the spacetime is regular. We also demonstrate that such an equivalence continues to hold even when the gravitational field equations are projected on a lower-dimensional hypersurface. We have further addressed explicit examples in which the solutions for Einstein-Hilbert and a scalar field system lead to solutions of the equivalent higher curvature theory. The same, but on the lower-dimensional hypersurface, has been illustrated in the reverse order as well. We conclude with a brief discussion on this technique of solving higher curvature field equations. (orig.)
Kinetic Quantum Theory of Gravity
DeAquino, F
2002-01-01
Gravity is here quantized starting from the generalization of the action function. This leads to an equation of correlation between gravitational and inertial masses, which depends on the particle's kinetic energy. We show that there is a reaffirmation of the strong equivalence principle and consequently the Einstein's equations are preserved. In fact such equations are deduced here directly from this kinetic approach to Gravity. Moreover, we have obtained a generalized equation for inertial forces, which incorporates the Mach's principle into Gravitation. Also, we have deduced the equation of Entropy; the Hamiltonian for a particle in an electromagnetic field and the reciprocal fine structure constant. It is possible to deduce the expression of the Casimir force and also to explain the Inflation Period and the Missing Matter without assuming the existence of vacuum fluctuations. This new approach for Gravity will allow us to understand some crucial matters in Cosmology.
Generalized gravity from modified DFT
Sakatani, Yuho; Yoshida, Kentaroh
2016-01-01
Recently, generalized equations of type IIB supergravity have been derived from the requirement of classical kappa-symmetry of type IIB superstring theory in the Green-Schwarz formulation. These equations are covariant under generalized T-duality transformations and hence one may expect a formulation similar to double field theory (DFT). In this paper, we consider a modification of the DFT equations of motion by relaxing a condition for the generalized covariant derivative with an extra generalized vector. In this modified double field theory (mDFT), we show that the flatness condition of the modified generalized Ricci tensor leads to the NS-NS part of the generalized equations of type IIB supergravity. In particular, the extra vector fields appearing in the generalized equations correspond to the extra generalized vector in mDFT. We also discuss duality symmetries and a modification of the string charge in mDFT.
Brans–Dicke gravity theory from topological gravity
Energy Technology Data Exchange (ETDEWEB)
Inostroza, C.; Salazar, A.; Salgado, P.
2014-06-27
We consider a model that suggests a mechanism by which the four dimensional Brans–Dicke gravity theory may emerge from the topological gravity action. To achieve this goal, both the Lie algebra and the symmetric invariant tensor that define the topological gravity Lagrangian are constructed by means of the Lie algebra S-expansion procedure with an appropriate abelian semigroup S.
The Origin of Structures in Generalized Gravity
Hwang, J
1998-01-01
In a class of generalized gravity theories with general couplings between the scalar field and the scalar curvature in the Lagrangian, we can describe the quantum generation and the classical evolution of both the scalar and tensor structures in a simple and unified manner. An accelerated expansion phase based on the generalized gravity in the early universe drives microscopic quantum fluctuations inside a causal domain to expand into macroscopic ripples in the spacetime metric on scales larger than the local horizon. Following their generation from quantum fluctuations, the ripples in the metric spend a long period outside the causal domain. During this phase their evolution is characterized by their conserved amplitudes. The evolution of these fluctuations may lead to the observed large scale structures of the universe and anisotropies in the cosmic microwave background radiation.
Gravitational Decoherence, Alternative Quantum Theories and Semiclassical Gravity
Hu, B L
2014-01-01
In this report we discuss three aspects: 1) Semiclassical gravity theory (SCG): 4 levels of theories describing the interaction of quantum matter with classical gravity; 2) Alternative Quantum Theories: Discerning those which are derivable from general relativity (GR) plus quantum field theory (QFT) from those which are not; 3) Gravitational Decoherence: Derivation of a master equation and examination of the assumptions which led to the claims of observational possibilities. We list three sets of corresponding problems worthy of pursuit: a) Newton-Schr\\"odinger Equations in relation to SCG; b) Master equation of gravity-induced effects serving as discriminator of 2); and c) Role of gravity in macroscopic quantum phenomena.
Chern-Simons-like Gravity Theories
Bergshoeff, Eric A.; Hohm, Olaf; Merbis, Wout; Routh, Alasdair J.; Townsend, Paul K.
2014-01-01
A wide class of three-dimensional gravity models can be put into "Chern-Simons-like" form. We perform a Hamiltonian analysis of the general model and then specialise to Einstein-Cartan Gravity, General Massive Gravity, the recently proposed Zwei-Dreibein Gravity and a further parity violating
Kinetic Quantum Theory of Gravity
DeAquino, F
2002-01-01
Starting from the action function we have derived a theoretical background that leads to quantization of gravity and the deduction of a correlation between the gravitational and inertial masses, which depends on the kinetic momentum of the particle. We show that there is a reaffirmation of the strong equivalence principle and consequently the Einstein's equations are preserved. In fact such equations are deduced here directly from this kinetic approach to Gravity. Moreover, we have obtained a generalized equation for inertial forces, which incorporates the Mach's principle into Gravitation. Also, we have deduced the equation of Entropy; the Hamiltonian for a particle in an electromagnetic field and the reciprocal fine structure constant. It is possible to deduce the expression of the Casimir force and also to explain the Inflation Period and the Missing Matter without assuming the existence of vacuum fluctuations. This new approach for Gravity will allow us to understand some crucial matters in Cosmology.
Directory of Open Access Journals (Sweden)
Rabounski D.
2007-07-01
Full Text Available We consider the Podkletnov effect — the weight loss of an object located over a superconducting disc in air due to support by an alternating magnetic field. We consider this problem using the mathematical methods of General Relativity. We show via Einstein’s equations and the geodesic equations in a space perturbed by a disc undergoing oscillatory bounces orthogonal to its own plane, that there is no r ˆ ole of superconductivity; the Podkletnov effect is due to the fact that the field of the background space non-holonomity (the basic non-othogonality of time lines to the spatial section, being perturbed by such an oscillating disc produces energy and momentum flow in order to compensate the perturbation in itself. Such a momentum flow is directed above the disc in Podkletnov’s experiment, so it works like negative gravity (anti-gravity. We propose a simple mechanical system which, simulating the Podkletnov effect, is an experimental test of the whole theory. The theory allows for other “anti-gravity devices”, which simulate the Podkletnov effect without use of very costly superconductor technology. Such devices could be applied to be used as a cheap source of new energy, and could have implications to air and space travel.
Extended Scalar-Tensor Theories of Gravity
Crisostomi, Marco; Tasinato, Gianmassimo
2016-01-01
We determine new consistent scalar-tensor theories of gravity, with potentially interesting cosmological applications. We develop a general method to find the conditions for the existence of a primary constraint, which is necessary to prevent the propagation of an additional dangerous mode associated with higher order equations of motion. We then classify the most general, consistent scalar-tensor theories that are at most quadratic in the second derivatives of the scalar field. In addition, we investigate the possible connection between these theories and (beyond) Horndeski through conformal and disformal transformations. Finally, we point out that these theories can be associated with new operators in the effective field theory of dark energy, which might open up new possibilities to test dark energy models in future surveys.
Extremal Black Hole in a Nonlinear Newtonian Theory of Gravity
Good, Michael R R
2008-01-01
This work investigates an upper-limit of charge for a black hole in a nonlinear Newtonian theory of gravity. The charge is accumulated via protons fired isotropically at the black hole. This theoretical study of gravity (known as `pseudo-Newtonian') is a forced merger of special relativity and Newtonian gravity. Whereas the source of Newton's gravity is purely mass, pseudo-Newtonian gravity includes effects of fields around the mass, giving a more complete picture of how gravity behaves. Interestingly, pseudo-Newtonian gravity predicts such relativistic phenomena as black holes and deviations from Kepler's laws, but of course, provides a less accurate picture than general relativity. Though less accurate, it offers an easier approach to understanding some results of general relativity, and merits interest due to its simplicity. The method of study applied here examines the predictions of pseudo-Newtonian gravity for a particle interacting with a highly charged black hole. A black hole with a suitable charge w...
Beyond generalized Proca theories
Directory of Open Access Journals (Sweden)
Lavinia Heisenberg
2016-09-01
Full Text Available We consider higher-order derivative interactions beyond second-order generalized Proca theories that propagate only the three desired polarizations of a massive vector field besides the two tensor polarizations from gravity. These new interactions follow the similar construction criteria to those arising in the extension of scalar–tensor Horndeski theories to Gleyzes–Langlois–Piazza–Vernizzi (GLPV theories. On the isotropic cosmological background, we show the existence of a constraint with a vanishing Hamiltonian that removes the would-be Ostrogradski ghost. We study the behavior of linear perturbations on top of the isotropic cosmological background in the presence of a matter perfect fluid and find the same number of propagating degrees of freedom as in generalized Proca theories (two tensor polarizations, two transverse vector modes, and two scalar modes. Moreover, we obtain the conditions for the avoidance of ghosts and Laplacian instabilities of tensor, vector, and scalar perturbations. We observe key differences in the scalar sound speed, which is mixed with the matter sound speed outside the domain of generalized Proca theories.
Beyond generalized Proca theories
Heisenberg, Lavinia; Kase, Ryotaro; Tsujikawa, Shinji
2016-09-01
We consider higher-order derivative interactions beyond second-order generalized Proca theories that propagate only the three desired polarizations of a massive vector field besides the two tensor polarizations from gravity. These new interactions follow the similar construction criteria to those arising in the extension of scalar-tensor Horndeski theories to Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories. On the isotropic cosmological background, we show the existence of a constraint with a vanishing Hamiltonian that removes the would-be Ostrogradski ghost. We study the behavior of linear perturbations on top of the isotropic cosmological background in the presence of a matter perfect fluid and find the same number of propagating degrees of freedom as in generalized Proca theories (two tensor polarizations, two transverse vector modes, and two scalar modes). Moreover, we obtain the conditions for the avoidance of ghosts and Laplacian instabilities of tensor, vector, and scalar perturbations. We observe key differences in the scalar sound speed, which is mixed with the matter sound speed outside the domain of generalized Proca theories.
Invariant conserved currents in generalized gravity
Obukhov, Yuri N; Puetzfeld, Dirk; Rubilar, Guillermo F
2015-01-01
We study conservation laws for gravity theories invariant under general coordinate transformations. The class of models under consideration includes Einstein's general relativity theory as a special case as well as its generalizations to non-Riemannian spacetime geometry and nonminimal coupling. We demonstrate that an arbitrary vector field on the spacetime manifold generates a current density that is conserved under certain conditions, and find the expression of the corresponding superpotential. For a family of models including nonminimal coupling between geometry and matter, we discuss in detail the differential conservation laws and the conserved quantities defined in terms of covariant multipole moments. We show that the equations of motion for the multipole moments of extended microstructured test bodies lead to conserved quantities that are closely related to the conserved currents derived in the field-theoretic framework.
Compact objects in relativistic theories of gravity
Okada da Silva, Hector
2017-05-01
In this dissertation we discuss several aspects of compact objects, i.e. neutron stars and black holes, in relativistic theories of gravity. We start by studying the role of nuclear physics (encoded in the so-called equation of state) in determining the properties of neutron stars in general relativity. We show that low-mass neutron stars are potentially useful astrophysical laboratories that can be used to constrain the properties of the equation of state. More specifically, we show that various bulk properties of these objects, such as their quadrupole moment and tidal deformability, are tightly correlated. Next, we develop a formalism that aims to capture how generic modifications from general relativity affect the structure of neutron stars, as predicted by a broad class of gravity theories, in the spirit of the parametrized post-Newtonian formalism (PPN). Our "post-Tolman-Oppenheimer-Volkoff" formalism provides a toolbox to study both stellar structure and the interior/exterior geometries of static, spherically symmetric relativistic stars. We also apply the formalism to parametrize deviations from general relativity in various astrophysical observables related with neutron stars, including surface redshift, apparent radius, Eddington luminosity. We then turn our attention to what is arguably the most well-motivated and well-investigated generalization of general relativity: scalar-tensor theory. We start by considering theories where gravity is mediated by a single extra scalar degree of freedom (in addition to the metric tensor). An interesting class of scalar-tensor theories passes all experimental tests in the weak-field regime of gravity, yet considerably deviates from general relativity in the strong-field regime in the presence of matter. A common assumption in modeling neutron stars is that the pressure within these object is spatially isotropic. We relax this assumption and examine how pressure anisotropy affects the mass, radius and moment of inertia
Finding Horndeski theories with Einstein gravity limits
McManus, Ryan; Lombriser, Lucas; Peñarrubia, Jorge
2016-11-01
The Horndeski action is the most general scalar-tensor theory with at most second-order derivatives in the equations of motion, thus evading Ostrogradsky instabilities and making it of interest when modifying gravity at large scales. To pass local tests of gravity, these modifications predominantly rely on nonlinear screening mechanisms that recover Einstein's Theory of General Relativity in regions of high density. We derive a set of conditions on the four free functions of the Horndeski action that examine whether a specific model embedded in the action possesses an Einstein gravity limit or not. For this purpose, we develop a new and surprisingly simple scaling method that identifies dominant terms in the equations of motion by considering formal limits of the couplings that enter through the new terms in the modified action. This enables us to find regimes where nonlinear terms dominate and Einstein's field equations are recovered to leading order. Together with an efficient approximation of the scalar field profile, one can then further evaluate whether these limits can be attributed to a genuine screening effect. For illustration, we apply the analysis to both a cubic galileon and a chameleon model as well as to Brans-Dicke theory. Finally, we emphasise that the scaling method also provides a natural approach for performing post-Newtonian expansions in screened regimes.
Perturbative Gravity and Gauge Theory Relations: A Review
Directory of Open Access Journals (Sweden)
Thomas Søndergaard
2012-01-01
Full Text Available This paper is dedicated to the amazing Kawai-Lewellen-Tye relations, connecting perturbative gravity and gauge theories at tree level. The main focus is on n-point derivations and general properties both from a string theory and pure field theory point of view. In particular, the field theory part is based on some very recent developments.
From General Relativity to Quantum Gravity
Ashtekar, Abhay; Rovelli, Carlo
2014-01-01
In general relativity (GR), spacetime geometry is no longer just a background arena but a physical and dynamical entity with its own degrees of freedom. We present an overview of approaches to quantum gravity in which this central feature of GR is at the forefront. However, the short distance dynamics in the quantum theory are quite different from those of GR and classical spacetimes and gravitons emerge only in a suitable limit. Our emphasis is on communicating the key strategies, the main results and open issues. In the spirit of this volume, we focus on a few avenues that have led to the most significant advances over the past 2-3 decades.
Ensemble average theory of gravity
Khosravi, Nima
2016-12-01
We put forward the idea that all the theoretically consistent models of gravity have contributions to the observed gravity interaction. In this formulation, each model comes with its own Euclidean path-integral weight where general relativity (GR) has automatically the maximum weight in high-curvature regions. We employ this idea in the framework of Lovelock models and show that in four dimensions the result is a specific form of the f (R ,G ) model. This specific f (R ,G ) satisfies the stability conditions and possesses self-accelerating solutions. Our model is consistent with the local tests of gravity since its behavior is the same as in GR for the high-curvature regime. In the low-curvature regime the gravitational force is weaker than in GR, which can be interpreted as the existence of a repulsive fifth force for very large scales. Interestingly, there is an intermediate-curvature regime where the gravitational force is stronger in our model compared to GR. The different behavior of our model in comparison with GR in both low- and intermediate-curvature regimes makes it observationally distinguishable from Λ CDM .
Generalised Boundary for Higher Derivative Theories of Gravity
Teimouri, Ali; Edholm, James; Mazumdar, Anupam
2016-01-01
In this paper we wish to find the corresponding Gibbons-Hawking-York term for the most general quadratic in curvature gravity by using Coframe slicing within the Arnowitt-Deser-Misner (ADM) decomposition of spacetime in four dimensions. In order to make sure that the higher derivative gravity is ghost and tachyon free at a perturbative level, one requires infinite covariant derivatives, which yields a generalised covariant infinite derivative theory of gravity. We will be exploring the boundary term for such a covariant infinite derivative theory of gravity.
Generalised boundary terms for higher derivative theories of gravity
Teimouri, Ali; Talaganis, Spyridon; Edholm, James; Mazumdar, Anupam
2016-08-01
In this paper we wish to find the corresponding Gibbons-Hawking-York term for the most general quadratic in curvature gravity by using Coframe slicing within the Arnowitt-Deser-Misner (ADM) decomposition of spacetime in four dimensions. In order to make sure that the higher derivative gravity is ghost and tachyon free at a perturbative level, one requires infinite covariant derivatives, which yields a generalised covariant infinite derivative theory of gravity. We will be exploring the boundary term for such a covariant infinite derivative theory of gravity.
Generalised boundary terms for higher derivative theories of gravity
Energy Technology Data Exchange (ETDEWEB)
Teimouri, Ali; Talaganis, Spyridon; Edholm, James [Consortium for Fundamental Physics, Lancaster University,North West Drive, Lancaster, LA1 4YB (United Kingdom); Mazumdar, Anupam [Consortium for Fundamental Physics, Lancaster University,North West Drive, Lancaster, LA1 4YB (United Kingdom); Kapteyn Astronomical Institute, University of Groningen,9700 AV Groningen (Netherlands)
2016-08-24
In this paper we wish to find the corresponding Gibbons-Hawking-York term for the most general quadratic in curvature gravity by using Coframe slicing within the Arnowitt-Deser-Misner (ADM) decomposition of spacetime in four dimensions. In order to make sure that the higher derivative gravity is ghost and tachyon free at a perturbative level, one requires infinite covariant derivatives, which yields a generalised covariant infinite derivative theory of gravity. We will be exploring the boundary term for such a covariant infinite derivative theory of gravity.
Causality in 3D Massive Gravity Theories
Edelstein, Jose D; Kilicarslan, Ercan; Leoni, Matias; Tekin, Bayram
2016-01-01
We study the constraints coming from local causality requirement in various 2+1 dimensional dynamical theories of gravity. In Topologically Massive Gravity, with a single parity noninvariant massive degree of freedom, and in New Massive Gravity, with two massive spin-$2$ degrees of freedom, causality and unitarity are compatible with each other and they both require the Newton's constant to be negative. In their extensions, such as the Born-Infeld gravity and the minimal massive gravity the situation is similar and quite different from their higher dimensional counterparts, such as quadratic (e.g., Einstein-Gauss-Bonnet) or cubic theories, where causality and unitarity are in conflict.
Quantum gravity from descriptive set theory
Energy Technology Data Exchange (ETDEWEB)
El Naschie, M.S
2004-03-01
We start from Hilbert's criticism of the axioms of classical geometry and the possibility of abandoning the Archimedean axiom. Subsequently we proceed to the physical possibility of a fundamental limitation on the smallest length connected to certain singular points in spacetime and below which measurements become meaningless, Finally we arrive at the conclusion that maximising the Hawking-Bekenstein informational content of spacetime makes the existence of a transfinite geometry for physical 'spacetime' not only plausible but probably inevitable. The main part of the paper is then concerned with a proposal for a mathematical description of a transfinite, non-Archimedean geometry using descriptive set theory. Nevertheless, and despite all abstract mathematics, we remain quite close to similar lines of investigation initiated by physicists like A. Wheeler, D. Finkelstein and G. 'tHooft. In particular we introduce a logarithmic gauge transformation linking classical gravity with the electro weak via a version of informational entropy. That way we may claim to have accomplished an important step towards a general theory of quantum gravity using {epsilon}{sup ({infinity}}{sup )} and complexity theory and finding that {alpha}{sub G}=(2){sup {alpha}}{sup -bar{sub ew-1}} congruent with (1.7)(10){sup 38} where {alpha}{sub G} is the dimensionless Newton gravity constant, and {alpha}{sub ew}{approx_equal}128 is the fine structure constant at the electro weak scale.
Stellar Pulsations in Beyond Horndeski Gravity Theories
Sakstein, Jeremy; Koyama, Kazuya
2016-01-01
Theories of gravity in the beyond Horndeski class recover the predictions of general relativity in the solar system whilst admitting novel cosmologies, including late-time de Sitter solutions in the absence of a cosmological constant. Deviations from Newton's law are predicted inside astrophysical bodies, which allow for falsifiable, smoking-gun tests of the theory. In this work we study the pulsations of stars by deriving and solving the wave equation governing linear adiabatic oscillations to find the modified period of pulsation. Using both semi-analytic and numerical models, we perform a preliminary survey of the stellar zoo in an attempt to identify the best candidate objects for testing the theory. Brown dwarfs and Cepheid stars are found to be particularly sensitive objects and we discuss the possibility of using both to test the theory.
Stellar pulsations in beyond Horndeski gravity theories
Sakstein, Jeremy; Kenna-Allison, Michael; Koyama, Kazuya
2017-03-01
Theories of gravity in the beyond Horndeski class recover the predictions of general relativity in the solar system whilst admitting novel cosmologies, including late-time de Sitter solutions in the absence of a cosmological constant. Deviations from Newton's law are predicted inside astrophysical bodies, which allow for falsifiable, smoking-gun tests of the theory. In this work we study the pulsations of stars by deriving and solving the wave equation governing linear adiabatic oscillations to find the modified period of pulsation. Using both semi-analytic and numerical models, we perform a preliminary survey of the stellar zoo in an attempt to identify the best candidate objects for testing the theory. Brown dwarfs and Cepheid stars are found to be particularly sensitive objects and we discuss the possibility of using both to test the theory.
General Covariance in Gravity at a Lifshitz Point
Horava, Petr
2011-01-01
This paper is based on the invited talks delivered by the author at GR 19: the 19th International Conference on General Relativity and Gravitation, Ciudad de M\\'exico, M\\'exico, July 2010. In Part 1, we briefly review some of the main features of quantum gravity with anisotropic scaling, and comment on its possible relation to the causal dynamical triangulations (CDT) approach to lattice quantum gravity. Part 2 explains the construction of gravity with anisotropic scaling with an extended gauge symmetry -- essentially a nonrelativistic version of general covariance. This extra symmetry eliminates the scalar graviton polarization, and thus brings the theory closer to general relativity at long distances.
Institute of Scientific and Technical Information of China (English)
WU Li-Li; WU Ning; HU Juan-Mei; WU Feng-Min
2008-01-01
For a long time, it has been generally believed that spin-spin interactions can only exist in a theory where Lorentz symmetry is gauged, and a theory with spin-spin interactions is not perturbatively renormalizable. But this is not true. By studying the motion of a spinning particle in gravitational field, it is found that there exist spin-spin interactions in gauge theory of gravity. Its mechanism is that a spinning particle will generate gravitomagnetic field in space-time, and this gravitomagnetic field will interact with the spin of another particle, which will cause spin-spin interactions. So, spin-spin interactions are transmitted by gravitational field. The form of spin-spin interactions in post Newtonian approximations is deduced. This result can also be deduced from the Papapetrou equation. This kind of interaction will not affect the renormalizability of the theory. The spin-spin interactions will violate the weak equivalence principle, and the violation effects are detectable. An experiment is proposed to detect the effects of the violation of the weak equivalence principle.
Weyl gravity as general relativity
Wheeler, James T
2013-01-01
When the full connection of Weyl conformal gravity is varied instead of just the metric, the resulting vacuum field equations reduce to the vacuum Einstein equation, up to the choice of local units. This result differs strongly from the usual fourth-order formulation of Weyl gravity.
Thermodynamics in Modified Gravity Theories
Bamba, Kazuharu; Tsujikawa, Shinji
2011-01-01
We demonstrate that there does exist an equilibrium description of thermodynamics on the apparent horizon in the expanding cosmological background for a wide class of modified gravity theories with the Lagrangian density $f(R, \\phi, X)$, where $R$ is the Ricci scalar and $X$ is the kinetic energy of a scalar field $\\phi$. This comes from a suitable definition of an energy momentum tensor of the "dark" component obeying the local energy conservation law in the Jordan frame. It is shown that the equilibrium description in terms of the horizon entropy $S$ is convenient because it takes into account the contribution of the horizon entropy $\\hat{S}$ in non-equilibrium thermodynamics as well as an entropy production term.
Acausality in Nonlocal Gravity Theory
Zhang, Ying-li; Sasaki, Misao; Zhao, Gong-Bo
2016-01-01
We investigate the nonlocal gravity theory by deriving nonlocal equations of motion using the traditional variation principle in a homogeneous background. We focus on a class of models with a linear nonlocal modification term in the action. It is found that the resulting equations of motion contain the advanced Green's function, implying that there is an acausality problem. As a consequence, a divergence arises in the solutions due to contributions from the future infinity unless the Universe will go back to the radiation dominated era or become the Minkowski spacetime in the future. We also discuss the relation between the original nonlocal equations and its biscalar-tensor representation and identify the auxiliary fields with the corresponding original nonlocal terms. Finally, we show that the acusality problem cannot be avoided by any function of nonlocal terms in the action.
Toward a gauge field theory of gravity.
Yilmaz, H.
Joint use of two differential identities (Bianchi and Freud) permits a gauge field theory of gravity in which the gravitational energy is localizable. The theory is compatible with quantum mechanics and is experimentally viable.
Chaotic inflation in higher derivative gravity theories
Myrzakul, Shynaray; Sebastiani, Lorenzo
2015-01-01
In this paper, we investigate chaotic inflation from scalar field subjected to potential in the framework of $f(R^2, P, Q)$-gravity, where we add a correction to Einstein's gravity based on a function of the square of the Ricci scalar $R^2$, the contraction of the Ricci tensor $P$, and the contraction of the Riemann tensor $Q$. The Gauss-Bonnet case is also discussed. We give the general formalism of inflation, deriving the slow-roll parameters, the $e$-folds number, and the spectral indexes. Several explicit examples are furnished, namely we will consider the cases of massive scalar field and scalar field with quartic potential and some power-law function of the curvature invariants under investigation in the gravitational action of the theory. Viable inflation according with observations is analyzed.
Holographic Theory of Gravity and Cosmology
Ng, Y Jack
2016-01-01
According to the holographic principle, the maximum amount of information stored in a region of space scales as the area of its two-dimensional surface, like a hologram. We show that the holographic principle can be understood heuristically as originated from quantum fluctuations of spacetime. Applied to cosmology, this consideration leads to a dynamical cosmological constant $\\Lambda$ of the observed magnitude, in agreement with the result obtained for the present and recent cosmic eras, by using unimodular gravity and causal-set theory. By generalizing the concept of entropic gravity, we find a critical acceleration parameter related to $\\Lambda$ in galactic dynamics, and we construct a phenomenological model of dark matter which we call "modified dark matter" (MDM). We provide successful observational tests of MDM at both the galactic and cluster scales. We also discuss the possibility that the quanta of both dark energy and dark matter obey the quantum Boltzmann statistics or infinite statistics as descri...
Chaotic inflation in higher derivative gravity theories
Energy Technology Data Exchange (ETDEWEB)
Myrzakul, Shynaray; Myrzakulov, Ratbay; Sebastiani, Lorenzo [Eurasian National University, Department of General and Theoretical Physics, Eurasian Center for Theoretical Physics, Astana (Kazakhstan)
2015-03-01
In this paper, we investigate chaotic inflation from a scalar field subjected to a potential in the framework of f(R{sup 2}, P, Q)-gravity, where we add a correction to Einstein's gravity based on a function of the square of the Ricci scalar R{sup 2}, the contraction of the Ricci tensor P, and the contraction of the Riemann tensor Q. The Gauss-Bonnet case is also discussed. We give the general formalism of inflation, deriving the slow-roll parameters, the e-fold number, and the spectral indices. Several explicit examples are furnished; namely, we will consider the cases of a massive scalar field and a scalar field with quartic potential and some power-law function of the curvature invariants under investigation in the gravitational action of the theory. A viable approach to inflation according with observations is analyzed. (orig.)
Ghost and singularity free theories of gravity
Buoninfante, L; Mazumdar, A
2016-01-01
Albert Einstein's General Relativity (GR) from 1916 has become the widely accepted theory of gravity and been tested observationally to a very high precision at different scales of energy and distance. At the same time, there still remain important questions to resolve. The presence of cosmological and black hole singularities are examples of problems at the classical level which strongly suggest the incompleteness of GR at short distances (high energy). Furthermore, at the quantum level GR is not UV complete, namely it is not perturbatively renormalizable. These two kind of questions, classical and quantum, could be closely related as both concern short-distance (high energy) physics. Most of the work try to solve these problems modifying GR by considering finite higher order derivative terms. Fourth Order Gravity, for example, turns out to be renormalizable, but at the same time it introduces ghost. To avoid both UV divergence and presence of ghost one could consider an infinite set of higher derivative ter...
GRAVITATIONAL LENSES AND UNCONVENTIONAL GRAVITY THEORIES
BEKENSTEIN, JD; SANDERS, RH
1994-01-01
We study gravitational lensing by clusters of galaxies in the context of the generic class of unconventional gravity theories which describe gravity in terms of a metric and one or more scalar fields (called here scalar-tensor theories). We conclude that, if the scalar fields have positive energy, t
GRAVITATIONAL LENSES AND UNCONVENTIONAL GRAVITY THEORIES
BEKENSTEIN, JD; SANDERS, RH
1994-01-01
We study gravitational lensing by clusters of galaxies in the context of the generic class of unconventional gravity theories which describe gravity in terms of a metric and one or more scalar fields (called here scalar-tensor theories). We conclude that, if the scalar fields have positive energy,
Local Poincaré Symmetry in Gauge Theory of Gravity
Institute of Scientific and Technical Information of China (English)
MA Jian-Feng; MA Yong-Ge
2009-01-01
It is well known that the Poincaré gauge theories of gravity do not have the structure of a standard gauge theory. Nevertheless, we show that a general form of action for the gravitational gauge fields in the gauge theory does possess local Poincaré invariance.
Generalized Vaidya spacetime for cubic gravity
Ruan, Shan-Ming
2015-01-01
We present a kind of generalized Vaidya solutions of a new cubic gravity in five dimensions whose field equations in spherically spacetime are always second order like the Lovelock gravity. We also study the thermodynamics of its apparent horizon and get its entropy expression and generalized Misner-Sharp energy. Finally we present the first law and second law hold in this gravity. Although all the results are analogue to those in Lovelock gravity, we in fact introduce the contribution of new cubic term in five dimensions where cubic Lovelock term is just zero.
Generalized quasi-dilaton theory
De Felice, Antonio; Mukohyama, Shinji
2013-01-01
Recently the first example of a unitary theory of Lorentz-invariant massive gravity allowing for stable self-accelerating de Sitter solutions was found, extending the quasidilaton theory. In this paper we further generalize this new action for the quasidilaton field by introducing general Lagrangian terms which are consistent with the quasidilaton symmetry while leading to second order equations of motion. We find that the structure of the theory, compared to the simplest stable example, does not change on introducing these new terms.
Local subsystems in gauge theory and gravity
Donnelly, William
2016-01-01
We consider the problem of defining localized subsystems in gauge theory and gravity. Such systems are associated to spacelike hypersurfaces with boundaries and provide the natural setting for studying entanglement entropy of regions of space. We present a general formalism to associate a gauge-invariant classical phase space to a spatial slice with boundary by introducing new degrees of freedom on the boundary. In Yang-Mills theory the new degrees of freedom are a choice of gauge on the boundary, transformations of which are generated by the normal component of the nonabelian electric field. In general relativity the new degrees of freedom are the location of a codimension-2 surface and a choice of conformal normal frame. These degrees of freedom transform under a group of surface symmetries, consisting of diffeomorphisms of the codimension-2 boundary, and position-dependent linear deformations of its normal plane. We find the observables which generate these symmetries, consisting of the conformal normal me...
Gravity duals for nonrelativistic conformal field theories.
Balasubramanian, Koushik; McGreevy, John
2008-08-08
We attempt to generalize the anti-de Sitter/conformal field theory correspondence to nonrelativistic conformal field theories which are invariant under Galilean transformations. Such systems govern ultracold atoms at unitarity, nucleon scattering in some channels, and, more generally, a family of universality classes of quantum critical behavior. We construct a family of metrics which realize these symmetries as isometries. They are solutions of gravity with a negative cosmological constant coupled to pressureless dust. We discuss realizations of the dust, which include a bulk superconductor. We develop the holographic dictionary and find two-point correlators of the correct form. A strange aspect of the correspondence is that the bulk geometry has two extra noncompact dimensions.
Signature change in loop quantum gravity: General midisuperspace models and dilaton gravity
Bojowald, Martin
2016-01-01
Models of loop quantum gravity based on real connections have a deformed notion of general covariance, which leads to the phenomenon of signature change. This result is confirmed here in a general analysis of all midisuperspace models without local degrees of freedom. As a subclass of models, 2-dimensional theories of dilaton gravity appear, but a larger set of examples is possible based only on the condition of anomaly freedom. While the classical dilaton gravity models are the only such systems without deformed covariance, they do give rise to signature change when holonomy modifications are included.
Phenomenology in minimal theory of massive gravity
Energy Technology Data Exchange (ETDEWEB)
Felice, Antonio De [Yukawa Institute for Theoretical Physics, Kyoto University,606-8502, Kyoto (Japan); Mukohyama, Shinji [Yukawa Institute for Theoretical Physics, Kyoto University,606-8502, Kyoto (Japan); Kavli Institute for the Physics and Mathematics of the Universe (WPI), University of Tokyo,277-8583, Chiba (Japan)
2016-04-15
We investigate the minimal theory of massive gravity (MTMG) recently introduced. After reviewing the original construction based on its Hamiltonian in the vielbein formalism, we reformulate it in terms of its Lagrangian in both the vielbein and the metric formalisms. It then becomes obvious that, unlike previous attempts in the literature of Lorentz-violating massive gravity, not only the potential but also the kinetic structure of the action is modified from the de Rham-Gabadadze-Tolley (dRGT) massive gravity theory. We confirm that the number of physical degrees of freedom in MTMG is two at fully nonlinear level. This proves the absence of various possible pathologies such as superluminality, acausality and strong coupling. Afterwards, we discuss the phenomenology of MTMG in the presence of a dust fluid. We find that on a flat homogeneous and isotropic background we have two branches. One of them (self-accelerating branch) naturally leads to acceleration without the genuine cosmological constant or dark energy. For this branch both the scalar and the vector modes behave exactly as in general relativity (GR). The phenomenology of this branch differs from GR in the tensor modes sector, as the tensor modes acquire a non-zero mass. Hence, MTMG serves as a stable nonlinear completion of the self-accelerating cosmological solution found originally in dRGT theory. The other branch (normal branch) has a dynamics which depends on the time-dependent fiducial metric. For the normal branch, the scalar mode sector, even though as in GR only one scalar mode is present (due to the dust fluid), differs from the one in GR, and, in general, structure formation will follow a different phenomenology. The tensor modes will be massive, whereas the vector modes, for both branches, will have the same phenomenology as in GR.
A Cosmological Study in Massive Gravity theory
Pan, Supriya
2015-01-01
A detailed study of the various cosmological aspects in massive gravity theory has been presented in the present work. For the homogeneous and isotropic FLRW model, the deceleration parameter has been evaluated, and, it has been examined whether there is any transition from deceleration to acceleration in recent past, or not. With the proper choice of the free parameters, it has been shown that the massive gravity theory is equivalent to Einstein gravity with a modified Newtonian gravitational constant together with a negative cosmological constant. Also, in this context, it has been examined whether the emergent scenario is possible, or not, in massive gravity theory. Finally, we have done a cosmographic analysis in massive gravity theory.
Quasi-local conserved charges in Lorenz-diffeomorphism covariant theory of gravity
Energy Technology Data Exchange (ETDEWEB)
Adami, H.; Setare, M.R. [University of Kurdistan, Department of Science, Sanandaj (Iran, Islamic Republic of)
2016-04-15
In this paper, using the combined Lorenz-diffeomorphism symmetry, we find a general formula for the quasi-local conserved charge of the covariant gravity theories in a first order formalism of gravity. We simplify the general formula for the Lovelock theory of gravity. Afterwards, we apply the obtained formula on BHT gravity to obtain the energy and angular momentum of the rotating OTT black hole solution in the context of this theory. (orig.)
Motion in alternative theories of gravity
Esposito-Farese, Gilles
2009-01-01
Although general relativity (GR) passes all present experimental tests with flying colors, it remains important to study alternative theories of gravity for several theoretical and phenomenological reasons that we recall in these lecture notes. The various possible ways of modifying GR are presented, and we notably show that the motion of massive bodies may be changed even if one assumes that matter is minimally coupled to the metric as in GR. This is illustrated with the particular case of scalar-tensor theories of gravity, whose Fokker action is discussed, and we also mention the consequences of the no-hair theorem on the motion of black holes. The finite size of the bodies modifies their motion with respect to pointlike particles, and we give a simple argument showing that the corresponding effects are generically much larger in alternative theories than in GR. We also discuss possible modifications of Newtonian dynamics (MOND) at large distances, which have been proposed to avoid the dark matter hypothesi...
A Simple Theory of Quantum Gravity
Horndeski, Gregory W
2015-01-01
A novel theory of Quantum Gravity is presented in which the real gravitons manifest themselves as holes in space. In general, these holes propagate at the speed of light through an expanding universe with boundary denoted by U, which is comprised of pulsating cells. These holes can form bound and semi-bound states. The geometry of U is non-Euclidean on a small scale, but there are indications that it can become Euclidean on a large scale. The motions of elementary particles through U are governed by probability 4 and 7-vectors, which are related to the momentum vectors in Minkowski space. The connection of this theory to Newtonian gravity is discussed, and an expression for the gravitational redshift of photons is derived which relates the redshift to the probability that a photon absorbs a virtual graviton. The theory also provides a possible explanation of dark matter and dark energy as gravitational phenomena, which do not require the introduction of any new particles. A quantum cosmology is presented in w...
The integrated bispectrum in modified gravity theories
Munshi, Dipak
2017-01-01
Gravity-induced non-Gaussianity can provide important clues to Modified Gravity (MG) Theories. Several recent studies have suggested using the Integrated Bispectrum (IB) as a probe for squeezed configuration of bispectrum. Extending previous studies on the IB, we include redshift-space distortions to study a class of (parametrised) MG theories that include the string-inspired Dvali, Gabadadze & Porrati (DGP) model. Various contributions from redshift-space distortions are derived in a transparent manner, and squeezed contributions from these terms are derived separately. Results are obtained using the Zel'dovich Approximation (ZA). Results are also presented for projected surveys (2D). We use the Press-Schechter (PS) and Sheth-Tormen (ST) mass functions to compute the IB for collapsed objects that can readily be extended to peak-theory based approaches. The cumulant correlators (CCs) generalise the ordinary cumulants and are known to probe collapsed configurations of higher order correlation functions. We generalise the concept of CCs to halos of different masses. We also introduce a generating function based approach to analyse more general non-local biasing models. The Fourier representations of the CCs, the skew-spectrum, or the kurt-spctra are discussed in this context. The results are relevant for the study of the Minkowski Functionals (MF) of collapsed tracers in redshift-space.
On field theory from gravity duals
Hockings, J R
2002-01-01
We review strings and branes in general, and then introduce the AdS/CFT Correspondence. The original work begins with an examination of the geometry for N = 4 on moduli space. We find a neat prescription for the encoding of the gravity solution in terms of the dual gauge theory. We next try to extend this to the N = 2* scenario, but encounter problems due to the gravity solution giving unexpected renormalization. Then we consider the correspondence applied to two field theories off their moduli spaces. We encounter unexpected problems with N = 2* again, but are successful in interpreting the Leigh-Strassler case. Finally, we apply the AdS/CFT correspondence to examine N = 4 super Yang-Mills at finite U(1) sub R charge density, using the supergravity backgrounds around spinning D3 branes. We complete the interpretation of the field theory duals of these backgrounds by interpreting the non-supersymmetric naked singularity class of the solutions. We find that these naked spinning D-brane distributions describe t...
Simulations of Solar System observations in alternative theories of gravity
Hees, A; Reynaud, S; Jaekel, M -T; Poncin-Lafitte, C Le; Lainey, V; Füzfa, A; Courty, J -M; Dehant, V; Wolf, P
2013-01-01
In this communication, we focus on the possibility to test General Relativity (GR) with radioscience experiments. We present simulations of observables performed in alternative theories of gravity using a software that simulates Range/Doppler signals directly from the space time metric. This software allows one to get the order of magnitude and the signature of the modifications induced by an alternative theory of gravity on radioscience signals. As examples, we present some simulations for the Cassini mission in Post-Einsteinian gravity (PEG) and with Standard Model Extension (SME).
Nichols, David A; Zhang, Fan; Zimmerman, Aaron; Brink, Jeandrew; Chen, Yanbei; Kaplan, Jeffrey D; Lovelace, Geoffrey; Matthews, Keith D; Scheel, Mark A; Thorne, Kip S
2011-01-01
When one splits spacetime into space plus time, the Weyl curvature tensor (vacuum Riemann tensor) gets split into two spatial, symmetric, and trace-free (STF) tensors: (i) the Weyl tensor's so-called "electric" part or tidal field, and (ii) the Weyl tensor's so-called "magnetic" part or frame-drag field. Being STF, the tidal field and frame-drag field each have three orthogonal eigenvector fields which can be depicted by their integral curves. We call the integral curves of the tidal field's eigenvectors tendex lines, we call each tendex line's eigenvalue its tendicity, and we give the name tendex to a collection of tendex lines with large tendicity. The analogous quantities for the frame-drag field are vortex lines, their vorticities, and vortexes. We build up physical intuition into these concepts by applying them to a variety of weak-gravity phenomena: a spinning, gravitating point particle, two such particles side by side, a plane gravitational wave, a point particle with a dynamical current-quadrupole mo...
Teleparallel Gravity in Five Dimensional Theories
Geng, Chao-Qiang; Tseng, Huan-Hsin
2014-01-01
We study teleparallel gravity in five-dimensional space-time with particular discussions on Kaluza-Klein (KK) and braneworld theories. We directly perform the dimensional reduction by differential forms. In the braneworld theory, the teleparallel gravity formalism in the Friedmann-Lema\\^{i}tre-Robertson-Walker cosmology is equivalent to GR due to the same Friedmann equation, whereas in the KK case the reduction of our formulation does not recover the effect as GR of 4-dimensional spacetime.
Stress-energy-momentum of affine-metric gravity generalized Komar superpotential
Giachetta, G
1995-01-01
In case of the Einstein's gravitation theory and its first order Palatini reformulation, the stress-energy-momentum of gravity has been proved to reduce to the Komar superpotential. We generalize this result to the affine-metric theory of gravity in case of general connections and arbitrary Lagrangian densities invariant under general covariant transformations. In this case, the stress-energy-momentum of gravity comes to the generalized Komar superpotential depending on a Lagrangian density in a precise way.
Thermodynamic properties of modified gravity theories
Bamba, Kazuharu
2016-01-01
We review thermodynamic properties of modified gravity theories such as $F(R)$ gravity and $f(T)$ gravity, where $R$ is the scalar curvature and $T$ is the torsion scalar in teleparallelism. In particular, we explore the equivalence between the equations of motion for modified gravity theories and the Clausius relation in thermodynamics. In addition, thermodynamics of the cosmological apparent horizon is investigated in $f(T)$ gravity. We show both equilibrium and non-equilibrium descriptions of thermodynamics. It is demonstrated that the second law of thermodynamics in the universe can be met when the temperature of the outside of the apparent horizon is equivalent to that of the inside of it.
Kaluza–Klein theory for teleparallel gravity
Energy Technology Data Exchange (ETDEWEB)
Geng, Chao-Qiang, E-mail: geng@phys.nthu.edu.tw [Chongqing University of Posts and Telecommunications, Chongqing, 400065 (China); Department of Physics, National Tsing Hua University, Hsinchu 300, Taiwan (China); Physics Division, National Center for Theoretical Sciences, Hsinchu 300, Taiwan (China); Lai, Chang, E-mail: laichang@cqupt.edu.cn [Chongqing University of Posts and Telecommunications, Chongqing, 400065 (China); Luo, Ling-Wei, E-mail: d9622508@oz.nthu.edu.tw [Department of Physics, National Tsing Hua University, Hsinchu 300, Taiwan (China); Tseng, Huan-Hsin, E-mail: d943335@oz.nthu.edu.tw [Department of Physics, National Tsing Hua University, Hsinchu 300, Taiwan (China)
2014-10-07
We study teleparallel gravity in the original Kaluza–Klein (KK) scenario. Our calculation of the KK reduction of teleparallel gravity indicates that the 5-dimensional torsion scalar {sup (5)}T generates the non-Brans–Dicke type effective Lagrangian in 4-dimension due to an additional coupling between the derivative of the scalar field and torsion, but the result is equivalent to that in general relativity. We also discuss the cosmological behavior in the FLRW universe based on the effective teleparallel gravity.
Perturbative Quantum Gravity and its Relation to Gauge Theory
Directory of Open Access Journals (Sweden)
Bern Zvi
2002-01-01
Full Text Available In this review we describe a non-trivial relationship between perturbative gauge theory and gravity scattering amplitudes. At the semi-classical or tree-level, the scattering amplitudes of gravity theories in flat space can be expressed as a sum of products of well defined pieces of gauge theory amplitudes. These relationships were first discovered by Kawai, Lewellen, and Tye in the context of string theory, but hold more generally. In particular, they hold for standard Einstein gravity. A method based on $D$-dimensional unitarity can then be used to systematically construct all quantum loop corrections order-by-order in perturbation theory using as input thegravity tree amplitudes expressed in terms of gauge theory ones. More generally, the unitarity method provides a means for perturbatively quantizing massless gravity theories without the usual formal apparatus associated with the quantization of constrained systems. As one application, this method was used to demonstrate that maximally supersymmetric gravity is less divergent in the ultraviolet than previously thought.
Higher order gravity theories and their black hole solutions
Charmousis, Christos
2008-01-01
We discuss a particular higher order gravity theory, Lovelock theory, that generalises in higher dimensions, general relativity. After briefly motivating modifications of gravity, we will introduce the theory in question and we will argue that it is a unique, mathematically sensible, and physically interesting extension of general relativity. We will see, by using the formalism of differential forms, the relation of Lovelock gravity to differential geometry and topology of even dimensional manifolds. We will then discuss a generic staticity theorem, which will give us the charged static black hole solutions. We will examine their asymptotic behavior, analyse their horizon structure and briefly their thermodynamics. We will then examine the distributional matching conditions for Lovelock theory. We will see how induced 4 dimensional Einstein-Hilbert terms result on the brane geometry from the higher order Lovelock terms. With the junction conditions at hand, we will go back to the black hole solutions and give...
Galactic space-times in modified theories of gravity
Dey, Dipanjan; Sarkar, Tapobrata
2014-01-01
We study Bertrand space-times (BSTs), which have been proposed as viable models of space-times seeded by galactic dark matter, in modified theories of gravity. We first critically examine the issue of galactic rotation curves in General Relativity, and establish the usefulness of BSTs to fit experimental data in this context. We then study BSTs in metric $f(R)$ gravity and in Brans-Dicke theories. For the former, the nature of the Newtonian potential is established, and we also compute the effective equation of state and show that it can provide good fits to some recent experimental results. For the latter, we calculate the Brans-Dicke scalar analytically in some limits and numerically in general, and find interesting constraints on the parameters of the theory. Our results provide evidence for the physical nature of Bertrand space-times in modified theories of gravity.
A new class of group field theories for 1st order discrete quantum gravity
Oriti, D.; Tlas, T.
2008-01-01
Group Field Theories, a generalization of matrix models for 2d gravity, represent a 2nd quantization of both loop quantum gravity and simplicial quantum gravity. In this paper, we construct a new class of Group Field Theory models, for any choice of spacetime dimension and signature, whose Feynman
A new class of group field theories for 1st order discrete quantum gravity
Oriti, D.; Tlas, T.
2008-01-01
Group Field Theories, a generalization of matrix models for 2d gravity, represent a 2nd quantization of both loop quantum gravity and simplicial quantum gravity. In this paper, we construct a new class of Group Field Theory models, for any choice of spacetime dimension and signature, whose Feynman a
A new class of group field theories for 1st order discrete quantum gravity
Oriti, D.; Tlas, T.
2008-01-01
Group Field Theories, a generalization of matrix models for 2d gravity, represent a 2nd quantization of both loop quantum gravity and simplicial quantum gravity. In this paper, we construct a new class of Group Field Theory models, for any choice of spacetime dimension and signature, whose Feynman a
Teleparallel equivalent theory of (1+ 1)-dimensional gravity
Institute of Scientific and Technical Information of China (English)
Gamal G.L. Nashed
2010-01-01
A theory of (1 +1)-dimensional gravity is constructed on the basis of the teleparallel equivalent of general relativity. The fundamental field variables are the tetrad fields ei~' and the gravity is attributed to the torsion. A dilatonic spherically symmetric exact solution of the gravitational field equations characterized by two parameters M and Q is derived. The energy associated with this solution is calculated using the two-dimensional gravitational energy-momentum formula.
Generalization Rough Set Theory
Institute of Scientific and Technical Information of China (English)
XIAO Di; ZHANG Jun-feng; HU Shou-song
2008-01-01
In order to avoid the discretization in the classical rough set theory, a generlization rough set theory is proposed.At first, the degree of general importance of an attribute and attribute subsets are presented.Then, depending on the degree of general importance of attribute, the space distance can be measured with weighted method.At last, a generalization rough set theory based on the general near neighborhood relation is proposed.The proposed theory partitions the universe into the tolerant modules, and forms lower approximation and upper approximation of the set under general near neighborhood relationship, which avoids the discretization in Pawlak's rough set theory.
A new class of group field theories for first order discrete quantum gravity
Energy Technology Data Exchange (ETDEWEB)
Oriti, D [Institute for Theoretical Physics and Spinoza Institute, Utrecht University, Leuvenlaan 4, Utrecht 3584 TD (Netherlands); Tlas, T [Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA (United Kingdom)], E-mail: d.oriti@phys.uu.nl, E-mail: t.tlas@damtp.cam.ac.uk
2008-04-21
Group field theories, a generalization of matrix models for 2D gravity, represent a second quantization of both loop quantum gravity and simplicial quantum gravity. In this paper, we construct a new class of group field theory models, for any choice of spacetime dimension and signature, whose Feynman amplitudes are given by path integrals for clearly identified discrete gravity actions, in first order variables. In the three-dimensional case, the corresponding discrete action is that of first order Regge calculus for gravity (generalized to include higher order corrections), while in higher dimensions, they correspond to a discrete BF theory (again, generalized to higher order) with an imposed orientation restriction on hinge volumes, similar to that characterizing discrete gravity. This new class of group field theories may represent a concrete unifying framework for loop quantum gravity and simplicial quantum gravity approaches.
Solar System constraints to general f(R) gravity
Chiba, T; Erickcek, A L; Chiba, Takeshi; Smith, Tristan L.; Erickcek, Adrienne L.
2006-01-01
It has been proposed that cosmic acceleration or inflation can be driven by replacing the Einstein-Hilbert action of general relativity with a function f(R) of the Ricci scalar R. Such f(R) gravity theories have been shown to be equivalent to scalar-tensor theories of gravity that are incompatible with Solar System tests of general relativity, as long as the scalar field propagates over Solar System scales. Specifically, the PPN parameter in the equivalent scalar-tensor theory is gamma=1/2, which is far outside the range allowed by observations. In response to a flurry of papers that questioned the equivalence of f(R) theory to scalar-tensor theories, it was recently shown explicitly, without resorting to the scalar-tensor equivalence, that the vacuum field equations for 1/R gravity around a spherically-symmetric mass also yield gamma= 1/2. Here we generalize this analysis to f(R) gravity and enumerate the conditions that, when satisfied by the function f(R), lead to the prediction that gamma=1/2.
Cosmological perturbation theory and quantum gravity
Brunetti, Romeo; Hack, Thomas-Paul; Pinamonti, Nicola; Rejzner, Katarzyna
2016-01-01
It is shown how cosmological perturbation theory arises from a fully quantized perturbative theory of quantum gravity. Central for the derivation is a non-perturbative concept of gauge-invariant local observables by means of which perturbative invariant expressions of arbitrary order are generated. In particular, in the linearised theory, first order gauge-invariant observables familiar from cosmological perturbation theory are recovered. Explicit expressions of second order quantities are presented as well.
Cosmological perturbation theory and quantum gravity
Energy Technology Data Exchange (ETDEWEB)
Brunetti, Romeo [Dipartimento di Matematica, Università di Trento,Via Sommarive 14, 38123 Povo TN (Italy); Fredenhagen, Klaus [II Institute für Theoretische Physik, Universität Hamburg,Luruper Chaussee 149, 22761 Hamburg (Germany); Hack, Thomas-Paul [Institute für Theoretische Physik, Universität Leipzig,Brüderstr. 16, 04103 Leipzig (Germany); Pinamonti, Nicola [Dipartimento di Matematica, Università di Genova,Via Dodecaneso 35, 16146 Genova (Italy); INFN, Sezione di Genova,Via Dodecaneso 33, 16146 Genova (Italy); Rejzner, Katarzyna [Department of Mathematics, University of York,Heslington, York YO10 5DD (United Kingdom)
2016-08-04
It is shown how cosmological perturbation theory arises from a fully quantized perturbative theory of quantum gravity. Central for the derivation is a non-perturbative concept of gauge-invariant local observables by means of which perturbative invariant expressions of arbitrary order are generated. In particular, in the linearised theory, first order gauge-invariant observables familiar from cosmological perturbation theory are recovered. Explicit expressions of second order quantities are presented as well.
Black holes in modified gravity theories
de la Cruz-Dombriz, Alvaro; Maroto, Antonio L
2010-01-01
In the context of $f(R)$ gravity theories, the issue of finding static and spherically symmetric black hole solutions is addressed. Two approaches to study the existence of such solutions are considered: first, constant curvature solutions, and second, the general case (without imposing constant curvature) is also studied. Performing a perturbative expansion around the Einstein-Hilbert action, it is found that only solutions of the Schwarzschild-(Anti-) de Sitter type are present (up to second order in perturbations) and the explicit expressions for these solutions are provided in terms of the $f(R)$ function. Finally we consider the thermodynamics of black holes in Anti-de Sitter space-time and study their local and global stability.
Quantum field theory II introductions to quantum gravity, supersymmetry and string theory
Manoukian, Edouard B
2016-01-01
This book takes a pedagogical approach to explaining quantum gravity, supersymmetry and string theory in a coherent way. It is aimed at graduate students and researchers in quantum field theory and high-energy physics. The first part of the book introduces quantum gravity, without requiring previous knowledge of general relativity (GR). The necessary geometrical aspects are derived afresh leading to explicit general Lagrangians for gravity, including that of general relativity. The quantum aspect of gravitation, as described by the graviton, is introduced and perturbative quantum GR is discussed. The Schwinger-DeWitt formalism is developed to compute the one-loop contribution to the theory and renormalizability aspects of the perturbative theory are also discussed. This follows by introducing only the very basics of a non-perturbative, background-independent, formulation of quantum gravity, referred to as “loop quantum gravity”, which gives rise to a quantization of space. In the second part the author in...
Black holes in three-dimensional dilaton gravity theories
Sá, P M; Lemos, J P S; Sa, Paulo M; Kleber, Antares; Lemos, Jose P S
1995-01-01
Three dimensional black holes in a generalized dilaton gravity action theory are analysed. The theory is specified by two fields, the dilaton and the graviton, and two parameters, the cosmological constant and the Brans-Dicke parameter. It contains seven different cases, of which one distinguishes as special cases, string theory, general relativity and a theory equivalent to four dimensional general relativity with one Killing vector. We study the causal structure and geodesic motion of null and timelike particles in the black hole geometries and find the ADM masses of the different solutions.
Compact stars in alternative theories of gravity. Einstein-Dilaton-Gauss-Bonnet gravity
Pani, Paolo; Cardoso, Vitor; Read, Jocelyn
2011-01-01
We develop a theoretical framework to study slowly rotating compact stars in a rather general class of alternative theories of gravity, with the ultimate goal of investigating constraints on alternative theories from electromagnetic and gravitational-wave observations of compact stars. Our Lagrangian includes as special cases scalar-tensor theories (and indirectly f(R) theories) as well as models with a scalar field coupled to quadratic curvature invariants. As a first application of the formalism, we discuss (for the first time in the literature) compact stars in Einstein-Dilaton-Gauss-Bonnet gravity. We show that compact objects with central densities typical of neutron stars cannot exist for certain values of the coupling constants of the theory. In fact, the existence and stability of compact stars sets more stringent constraints on the theory than the existence of black hole solutions. This work is a first step in a program to systematically rule out (possibly using Bayesian model selection) theories tha...
Compact stars in vector-tensor-Horndeski theory of gravity
Energy Technology Data Exchange (ETDEWEB)
Momeni, Davood; Myrzakulov, Kairat; Myrzakulov, Ratbay [Eurasian National University, Department of General and Theoretical Physics, Eurasian International Center for Theoretical Physics, Astana (Kazakhstan); Faizal, Mir [University of British Columbia-Okanagan, Irving K. Barber School of Arts and Sciences, Kelowna, BC (Canada); University of Lethbridge, Department of Physics and Astronomy, Lethbridge, AB (Canada)
2017-01-15
In this paper, we will analyze a theory of modified gravity, in which the field content of general relativity will be increased to include a vector field. We will use the Horndeski formalism to non-minimally couple this vector field to the metric. As we will be using the Horndeski formalism, this theory will not contain Ostrogradsky ghost degree of freedom. We will analyze compact stars using this vector-tensor-Horndeski theory. (orig.)
Testing gravity theories using tensor perturbations
Lin, Weikang; Ishak-Boushaki, Mustapha B.
2017-01-01
Primordial gravitational waves constitute a promising probe of the very early universe physics and the laws of gravity. We study the changes to tensor-mode perturbations that can arise in various modified gravity theories. These include a modified friction and a nonstandard dispersion relation. We introduce a physically motivated parametrization of these effects and use current data to obtain excluded parameter spaces. Taking into account the foreground subtraction, we then perform a forecast analysis focusing on the tensor-mode modified-gravity parameters as constrained by future experiments COrE, Stage-IV and PIXIE. For the tensor-to-scalar ratio r=0.01, we find the minimum detectible modified-gravity effects. In particular, the minimum detectable graviton mass is about 7.8˜9.7×10-33 eV, which is of the same order of magnitude as the graviton mass that allows massive gravity to produce late-time cosmic acceleration. Finally, we study the tensor-mode perturbations in modified gravity during inflation. We find that, the tensor spectral index would be additionally related to the friction parameter ν0 by nT=-3ν0-r/8. In some cases, the future experiments will be able to distinguish this relation from the standard one. In sum, primordial gravitational waves provide a complementary avenue to test gravity theories.
Torsion Wave Solutions in Yang-Mielke Theory of Gravity
Pasic, Vedad
2015-01-01
The approach of metric-affine gravity initially distinguishes it from Einstein's general relativity. Using an independent affine connection produces a theory with 10+64 unknowns. We write down the Yang-Mills action for the affine connection and produce the Yang-Mills equation and the so called complementary Yang-Mills equation by independently varying with respect to the connection and the metric respectively. We call this theory the Yang-Mielke theory of gravity. We construct explicit spacetimes with pp-metric and purely axial torsion and show that they represent a solution of Yang-Mills theory. Finally we compare these spacetimes to existing solutions of metric-affine gravity and present future research possibilities.
Comments on "Cahill's Quantum Foam Inflow Theory of Gravity"
Martin, T D
2004-01-01
We reveal an underlying flaw in Reginald T. Cahill's recently promoted quantum foam inflow theory of gravity. It appears to arise from a confusion of the idea of the Galilean invariance of the acceleration of an individual flow with what is obtained as an acceleration when a homogeneous flow is superposed with an inhomogeneous flow. We also point out that the General Relativistic covering theory he creates by substituting a generalized Painleve-Gullstrand metric into Einstein's field equations leads to absurd results.
Higher Gauge Theory and Gravity in (2+1) Dimensions
Mann, R B; Popescu, Eugeniu M.
2006-01-01
Non-abelian higher gauge theory has recently emerged as a generalization of standard gauge theory to higher dimensional (2-dimensional in the present context) connection forms, and as such, it has been successfully applied to the non-abelian generalizations of the Yang-Mills theory and 2-form electrodynamics. (2+1)-dimensional gravity, on the other hand, has been a fertile testing ground for many concepts related to classical and quantum gravity, and it is therefore only natural to investigate whether we can find an application of higher gauge theory in this latter context. In the present paper we investigate the possibility of applying the formalism of higher gauge theory to gravity in (2+1) dimensions, and we show that a nontrivial model of (2+1)-dimensional gravity coupled to scalar and tensorial matter fields - the $\\Sigma\\Phi EA$ model - can be formulated both as a standard gauge theory and as a higher gauge theory. Since the model has a very rich structure - it admits as solutions black-hole BTZ-like ge...
Gauge theories of gravity: the nonlinear framework
Tiemblo, A
2004-01-01
Nonlinear realizations of spacetime groups are presented as a versatile mathematical tool providing a common foundation for quite different formulations of gauge theories of gravity. We apply nonlinear realizations in particular to both the Poincar\\'e and the affine group in order to develop Poincar\\'e gauge theory (PGT) and metric-affine gravity (MAG) respectively. Regarding PGT, two alternative nonlinear treatments of the Poincar\\'e group are developed, one of them being suitable to deal with the Lagrangian and the other one with the Hamiltonian version of the same gauge theory. We argue that our Hamiltonian approach to PGT is closely related to Ashtekar's approach to gravity. On the other hand, a brief survey on MAG clarifies the role played by the metric--affine metric tensor as a Goldsone field. All gravitational quantities in fact --the metric as much as the coframes and connections-- are shown to acquire a simple gauge--theoretical interpretation in the nonlinear framework.
A New Class of Group Field Theories for 1st Order Discrete Quantum Gravity
Oriti, D; Tlas, T.
2007-01-01
Group Field Theories, a generalization of matrix models for 2d gravity, represent a 2nd quantization of both loop quantum gravity and simplicial quantum gravity. In this paper, we construct a new class of Group Field Theory models, for any choice of spacetime dimension and signature, whose Feynman amplitudes are given by path integrals for clearly identified discrete gravity actions, in 1st order variables. In the 3-dimensional case, the corresponding discrete action is that of 1st order Regg...
Eddington's theory of gravity and its progeny.
Bañados, Máximo; Ferreira, Pedro G
2010-07-01
We resurrect Eddington's proposal for the gravitational action in the presence of a cosmological constant and extend it to include matter fields. We show that the Newton-Poisson equation is modified in the presence of sources and that charged black holes show great similarities with those arising in Born-Infeld electrodynamics coupled to gravity. When we consider homogeneous and isotropic space-times, we find that there is a minimum length (and maximum density) at early times, clearly pointing to an alternative theory of the big bang. We thus argue that the modern formulation of Eddington's theory, Born-Infeld gravity, presents us with a novel, nonsingular description of the Universe.
A New Class of Group Field Theories for 1st Order Discrete Quantum Gravity
Oriti, Daniele
2007-01-01
Group Field Theories, a generalization of matrix models for 2d gravity, represent a 2nd quantization of both loop quantum gravity and simplicial quantum gravity. In this paper, we construct a new class of Group Field Theory models, for any choice of spacetime dimension and signature, whose Feynman amplitudes are given by path integrals for clearly identified discrete gravity actions, in 1st order variables. In the 3-dimensional case, the corresponding discrete action is that of 1st order Regge calculus for gravity (generalized to include higher order corrections), while in higher dimensions, they correspond to a discrete BF-theory (again, generalized to higher order) with an imposed orientation restriction on hinge volumes, similar to that characterizing discrete gravity. The new models shed also light on the large distance or semi-classical approximation of spin foam models. This new class of group field theories may represent a concrete unifying framework for loop quantum gravity and simplicial quantum grav...
Kaluza–Klein theory for teleparallel gravity
Directory of Open Access Journals (Sweden)
Chao-Qiang Geng
2014-10-01
Full Text Available We study teleparallel gravity in the original Kaluza–Klein (KK scenario. Our calculation of the KK reduction of teleparallel gravity indicates that the 5-dimensional torsion scalar T(5 generates the non-Brans–Dicke type effective Lagrangian in 4-dimension due to an additional coupling between the derivative of the scalar field and torsion, but the result is equivalent to that in general relativity. We also discuss the cosmological behavior in the FLRW universe based on the effective teleparallel gravity.
Kaluza-Klein theory for teleparallel gravity
Geng, Chao-Qiang; Luo, Ling-Wei; Tseng, Huan-Hsin
2014-01-01
We study teleparallel gravity in the \\emph{original} Kaluza-Klein (KK) scenario. Our calculation of the KK reduction of teleparallel gravity indicates that the 5-dimensional torsion scalar $^{(5)}T$ generates the non-Brans-Dicke type effective Lagrangian in 4-dimension due to an additional coupling between the derivative of the scalar field and torsion, but the result is equivalent to that in general relativity. We also discuss the cosmological behavior in the FLRW universe based on the effective teleparallel gravity.
String Theory, Unification and Quantum Gravity
Stelle, K S
2012-01-01
An overview is given of the way in which the unification program of particle physics has evolved into the proposal of superstring theory as a prime candidate for unifying quantum gravity with the other forces and particles of nature. A key concern with quantum gravity has been the problem of ultraviolet divergences, which is naturally solved in string theory by replacing particles with spatially extended states as the fundamental excitations. String theory turns out, however, to contain many more extended-object states than just strings. Combining all this into an integrated picture, called M-theory, requires recognition of the r\\^ole played by a web of nonperturbative duality symmetries suggested by the nonlinear structures of the field-theoretic supergravity limits of string theory.
Generalized BF state in quantum gravity
Yamashita, Shinji; Fukuda, Makoto
2014-01-01
The BF state is known as a simple wave function which satisfies three constraints in canonical quantum gravity without a cosmological constant. It is constructed from a product of the group delta functions. Applying the chiral asymmetric extension, the BF state is generalized to the state for the real values of the Barbero-Immirzi parameter.
Generalized Higher Gauge Theory
Ritter, Patricia; Schmidt, Lennart
2015-01-01
We study a generalization of higher gauge theory which makes use of generalized geometry and seems to be closely related to double field theory. The local kinematical data of this theory is captured by morphisms of graded manifolds between the canonical exact Courant Lie 2-algebroid $TM\\oplus T^*M$ over some manifold $M$ and a semistrict gauge Lie 2-algebra. We discuss generalized curvatures and their infinitesimal gauge transformations. Finite gauge transformation as well as global kinematical data are then obtained from principal 2-bundles over 2-spaces. As dynamical principle, we consider first the canonical Chern-Simons action for such a gauge theory. We then show that a previously proposed 3-Lie algebra model for the six-dimensional (2,0) theory is very naturally interpreted as a generalized higher gauge theory.
A special fermionic generalization of lineal gravity
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
The central extension of the (1+1)-dimensional Poincaré algebra by including fermionic charges which obey not supersymmetric algebra, but a special graded algebra containing in the right hand side a central element only is obtained. The corresponding theory being the fermionic extension of the lineal gravity is proposed. We considered the algebra of generators, the field transformations and found Lagrangian and equation of motion, then we derived the Casimir operator and obtained the constant black hole mass.
CDT: an entropic theory of quantum gravity
Ambjorn, J.; Goerlich, A.; Jurkiewicz, J.; Loll, R.
2010-01-01
In these lectures we describe how a theory of quantum gravity may be constructed in terms of a lattice formulation based on so-called causal dynamical triangulations (CDT). We discuss how the continuum limit can be obtained and how to define and measure diffeomorphism-invariant correlators. In four
Extended Theories of Gravity in cosmological and astrophysical applications
Wojnar, Aneta
2016-01-01
The main subjects of the PhD dissertation concern cosmological models considered in Palatini f(R) gravity and scalar-tensor theories. We introduce a simple generalization of the LCDM model based on Palatini modified gravity with quadratic Starobinsky term. A matter source is provided by generalized Chaplygin gas. The statistical analysis of our model is investigated. We use dynamical system approach to study the evolution of the Universe. The model reaches a very good agreement with the newest experimental data and yields an inflationary epoch caused by a singularity of the type III. The present-day accelerated expansion is also provided by the model. We also show that the Lie and Noether symmetry approaches are very useful tools in cosmological considerations. We examine two other models of Extended Theories of Gravity (ETGs): the novel hybrid metric-Palatini gravity and a minimally coupled to gravity scalar field. The first one is applied to homogeneous and isotropic model while in the scalar-tensor theory ...
Black hole hair in generalized scalar-tensor gravity
Sotiriou, Thomas P
2013-01-01
The most general action for a scalar field coupled to gravity that leads to second order field equations for both the metric and the scalar --- Horndeski's theory --- is considered, with the extra assumption that the scalar satisfies shift symmetry. We show that in such theories the scalar field is forced to have a nontrivial configuration in black hole spacetimes, unless one carefully tunes away a linear coupling with the Gauss--Bonnet invariant. Hence, black holes for generic theories in this class will have hair. This contradicts a recent no-hair theorem, which seems to have overlooked the presence of this coupling.
Strong Gravity Approach to QCD and General Relativity
Akinto, O F
2016-01-01
A systematic study of the Weyl-type / Yang-Mills-type action possessing local conformal invariance and quadratic curvature is undertaken. The dynamical breaking of this conformal invariance / scale invariance induces general relativity (GR) as an effective long distance limit of the theory. We prove that the corresponding field equations of the theory have the linearly rising potential, which naturally possesses asymptotic freedom and color confinement properties of quantum chromodynamics (QCD). Solutions to the neutrino mass and dark energy problems come as free gifts of this formulation. This approach provides a strong gravity basis for the unification of quantum Yang-Mills theory (QYMT) with Einstein GR.
Black hole hair in generalized scalar-tensor gravity.
Sotiriou, Thomas P; Zhou, Shuang-Yong
2014-06-27
The most general action for a scalar field coupled to gravity that leads to second-order field equations for both the metric and the scalar--Horndeski's theory--is considered, with the extra assumption that the scalar satisfies shift symmetry. We show that in such theories, the scalar field is forced to have a nontrivial configuration in black hole spacetimes, unless one carefully tunes away a linear coupling with the Gauss-Bonnet invariant. Hence, black holes for generic theories in this class will have hair. This contradicts a recent no-hair theorem which seems to have overlooked the presence of this coupling.
From thermodynamics to the solutions in gravity theory
Directory of Open Access Journals (Sweden)
Hongsheng Zhang
2014-10-01
Full Text Available In a recent work, we present a new point of view to the relation of gravity and thermodynamics, in which we derive the Schwarzschild solution through thermodynamic considerations by the aid of the Misner–Sharp mass in an adiabatic system. In this Letter we continue to investigate the relation between gravity and thermodynamics for obtaining solutions via thermodynamics. We generalize our studies on gravi-thermodynamics in Einstein gravity to modified gravity theories. By using the first law with the assumption that the Misner–Sharp mass is the mass for an adiabatic system, we reproduce the Boulware–Deser–Cai solution in Gauss–Bonnet gravity. Using this gravi-thermodynamic thought, we obtain a NEW class of solution in F(R gravity in an n-dimensional (n≥3 spacetime which permits three-type (n−2-dimensional maximally symmetric subspace, as an extension of our recent three-dimensional black hole solution, and four-dimensional Clifton–Barrow solution in F(R gravity.
The Integrated Bispectrum in Modified Gravity Theories
Munshi, Dipak
2016-01-01
Gravity-induced non-Gaussianity can provide important clues to Modified Gravity (MG) Theories. Several recent studies have suggested using the {\\it Integrated Bispectrum} (IB) as a probe for squeezed configuration of bispectrum. Extending previous studies on the IB, we include redshift-space distortions to study a class of (parametrised) MG theories that include the string-inspired Dvali, Gabadadze \\& Porrati (DGP) model. Various contributions from redshift-space distortions are derived in a transparent manner, and squeezed contributions from these terms are derived separately. Results are obtained using the Zel'dovich Approximation (ZA). Results are also presented for projected surveys (2D). We use the Press-Schechter (PS) and Sheth-Torman (ST) mass functions to compute the IB for collapsed objects that can readily be extended to peak-theory based approaches. The {\\em cumulant correlators} (CCs) generalise the ordinary {\\em cumulants} and are known to probe collapsed configurations of higher order correl...
Weak gravity conjecture and effective field theory
Saraswat, Prashant
2017-01-01
The weak gravity conjecture (WGC) is a proposed constraint on theories with gauge fields and gravity, requiring the existence of light charged particles and/or imposing an upper bound on the field theory cutoff Λ . If taken as a consistency requirement for effective field theories (EFTs), it rules out possibilities for model building including some models of inflation. I demonstrate simple models which satisfy all forms of the WGC, but which through Higgsing of the original gauge fields produce low-energy EFTs with gauge forces that badly violate the WGC. These models illustrate specific loopholes in arguments that motivate the WGC from a bottom-up perspective; for example the arguments based on magnetic monopoles are evaded when the magnetic confinement that occurs in a Higgs phase is accounted for. This indicates that the WGC should not be taken as a veto on EFTs, even if it turns out to be a robust property of UV quantum gravity theories. However, if the latter is true, then parametric violation of the WGC at low energy comes at the cost of nonminimal field content in the UV. I propose that only a very weak constraint is applicable to EFTs, Λ ≲(log 1/g )-1 /2Mpl , where g is the gauge coupling, motivated by entropy bounds. Remarkably, EFTs produced by Higgsing a theory that satisfies the WGC can saturate but not violate this bound.
On adiabatic invariant in generalized Galileon theories
Ema, Yohei; Mukaida, Kyohei; Nakayama, Kazunori
2015-01-01
We consider background dynamics of generalized Galileon theories in the context of inflation, where gravity and inflaton are non-minimally coupled to each other. In the inflaton oscillation regime, the Hubble parameter and energy density oscillate violently in many cases, in contrast to the Einstein gravity with minimally coupled inflaton. However, we find that there is an adiabatic invariant in the inflaton oscillation regime in any generalized Galileon theory. This adiabatic invariant is useful in estimating the expansion law of the universe and also the particle production rate due to the oscillation of the Hubble parameter.
Testing gravity theories using tensor perturbations
Lin, Weikang; Ishak, Mustapha
2016-12-01
Primordial gravitational waves constitute a promising probe of the very early Universe and the laws of gravity. We study in this work changes to tensor-mode perturbations that can arise in various proposed modified gravity theories. These include additional friction effects, nonstandard dispersion relations involving a massive graviton, a modified speed, and a small-scale modification. We introduce a physically motivated parametrization of these effects and use current available data to obtain exclusion regions in the parameter spaces. Taking into account the foreground subtraction, we then perform a forecast analysis focusing on the tensor-mode modified-gravity parameters as constrained by the future experiments COrE, Stage-IV and PIXIE. For a fiducial value of the tensor-to-scalar ratio r =0.01 , we find that an additional friction of 3.5-4.5% compared to GR will be detected at 3 -σ by these experiments, while a decrease in friction will be more difficult to detect. The speed of gravitational waves needs to be by 5-15% different from the speed of light for detection. We find that the minimum detectable graviton mass is about 7.8 - 9.7 ×10-33 eV , which is of the same order of magnitude as the graviton mass that allows massive gravity theories to produce late-time cosmic acceleration. Finally, we study the tensor-mode perturbations in modified gravity during inflation using our parametrization. We find that, in addition to being related to r , the tensor spectral index would be related to the friction parameter ν0 by nT=-3 ν0-r /8 . Assuming that the friction parameter is unchanged throughout the history of the Universe, and that ν0 is much larger than r , the future experiments considered here will be able to distinguish this modified-gravity consistency relation from the standard inflation consistency relation, and thus can be used as a further test of modified gravity. In summary, tensor-mode perturbations and cosmic-microwave-background B
A gauge theory of gravity in curved phase-spaces
Castro, Carlos
2016-06-01
After a cursory introduction of the basic ideas behind Born’s Reciprocal Relativity theory, the geometry of the cotangent bundle of spacetime is studied via the introduction of nonlinear connections associated with certain nonholonomic modifications of Riemann-Cartan gravity within the context of Finsler geometry. A novel gauge theory of gravity in the 8D cotangent bundle T∗M of spacetime is explicitly constructed and based on the gauge group SO(6, 2) ×sR8 which acts on the tangent space to the cotangent bundle T(x,p)T∗M at each point (x,p). Several gravitational actions involving curvature and torsion tensors and associated with the geometry of curved phase-spaces are presented. We conclude with a brief discussion of the field equations, the geometrization of matter, quantum field theory (QFT) in accelerated frames, T-duality, double field theory, and generalized geometry.
Generalized etale cohomology theories
Jardine, John F
1997-01-01
A generalized etale cohomology theory is a theory which is represented by a presheaf of spectra on an etale site for an algebraic variety, in analogy with the way an ordinary spectrum represents a cohomology theory for spaces. Examples include etale cohomology and etale K-theory. This book gives new and complete proofs of both Thomason's descent theorem for Bott periodic K-theory and the Nisnevich descent theorem. In doing so, it exposes most of the major ideas of the homotopy theory of presheaves of spectra, and generalized etale homology theories in particular. The treatment includes, for the purpose of adequately dealing with cup product structures, a development of stable homotopy theory for n-fold spectra, which is then promoted to the level of presheaves of n-fold spectra. This book should be of interest to all researchers working in fields related to algebraic K-theory. The techniques presented here are essentially combinatorial, and hence algebraic. An extensive background in traditional stable hom...
Baryogenesis in Lorentz-violating gravity theories
Sakstein, Jeremy; Solomon, Adam R.
2017-10-01
Lorentz-violating theories of gravity typically contain constrained vector fields. We show that the lowest-order coupling of such vectors to U (1)-symmetric scalars can naturally give rise to baryogenesis in a manner akin to the Affleck-Dine mechanism. We calculate the cosmology of this new mechanism, demonstrating that a net B - L can be generated in the early Universe, and that the resulting baryon-to-photon ratio matches that which is presently observed. We discuss constraints on the model using solar system and astrophysical tests of Lorentz violation in the gravity sector. Generic Lorentz-violating theories can give rise to the observed matter-antimatter asymmetry without violating any current bounds.
Eddington's Theory of Gravity and Its Progeny
Bañados, Máximo; Ferreira, Pedro G.
2010-07-01
We resurrect Eddington’s proposal for the gravitational action in the presence of a cosmological constant and extend it to include matter fields. We show that the Newton-Poisson equation is modified in the presence of sources and that charged black holes show great similarities with those arising in Born-Infeld electrodynamics coupled to gravity. When we consider homogeneous and isotropic space-times, we find that there is a minimum length (and maximum density) at early times, clearly pointing to an alternative theory of the big bang. We thus argue that the modern formulation of Eddington’s theory, Born-Infeld gravity, presents us with a novel, nonsingular description of the Universe.
Encoding field theories into gravities
Aoki, Sinya; Onogi, Tetsuya
2016-01-01
We propose a method to give a $d+1$ geometry from a $d$ dimensional quantum field theory in the large N expansion. We first construct a $d+1$ dimensional field from the $d$ dimensional one using the gradient flow equation, whose flow time $t$ represents the energy scale of the system such that $t\\rightarrow 0$ corresponds to the ultra-violet (UV) while $t\\rightarrow\\infty$ to the infra-red (IR). We define the induced metric using $d+1$ dimensional field operators. We show that the metric defined in this way becomes classical in the large N limit: quantum fluctuations of the metric are suppressed as 1/N due to the large $N$ factorization property. As a concrete example, we apply our method to the O(N) non-linear $\\sigma$ model in two dimensions. We calculate the three dimensional induced metric, which describes an AdS space in the massless limit. We finally discuss several open issues for future investigations.
Gravitational Shielding Effect in Gauge Theory of Gravity
Institute of Scientific and Technical Information of China (English)
WU Ning
2004-01-01
In 1992,E.E.Podkletnov and R.Nieminen found that under certain conditions,ceramic superconductor with composite structure reveals weak shielding properties against gravitational force.In classical Newton's theory of gravity and even in Einstein's general theory of gravity,there are no grounds of gravitational shielding effects.But in quantum gauge theory of gravity,the gravitational shielding effects can be explained in a simple and natural way.In quantum gauge theory of gravity,gravitational gauge interactions of complex scalar field can be formulated based on gauge principle.After spontaneous symmetry breaking,if the vacuum of the complex scalar field is not stable and uniform,there will be a mass term of gravitational gauge field.When gravitational gauge field propagates in this unstable vacuum of the complex scalar field,it will decays exponentially,which is the nature of gravitational shielding effects.The mechanism of gravitational shielding effects is studied in this paper,and some main properties of gravitational shielding effects are discussed.
Generalized quantum gravity condensates for homogeneous geometries and cosmology
Oriti, Daniele; Ryan, James P; Sindoni, Lorenzo
2015-01-01
We construct a generalized class of quantum gravity condensate states, that allows the description of continuum homogeneous quantum geometries within the full theory. They are based on similar ideas already applied to extract effective cosmological dynamics from the group field theory formalism, and thus also from loop quantum gravity. However, they represent an improvement over the simplest condensates used in the literature, in that they are defined by an infinite superposition of graph-based states encoding in a precise way the topology of the spatial manifold. The construction is based on the definition of refinement operators on spin network states, written in a second quantized language. The construction lends itself easily to be applied also to the case of spherically symmetric quantum geometries.
New Cosmological Solutions in Massive Gravity Theory
Pinho, S. S. A.; Pereira, S. H.; Mendonça, E. L.
2017-04-01
In this paper we present some new cosmological solutions in massive gravity theory. Some homogeneous and isotropic solutions correctly describe accelerated evolutions for the universe. The study was realized considering a specific form to the fiducial metric and found different functions and constant parameters of the theory that guarantee the conservation of the energy momentum tensor. Several accelerating cosmologies were found, all of them reproducing a cosmological constant term proportional to the graviton mass, with a de Sitter type solution for the scale factor. We have also verified that when the fiducial metric is close to the physical metric the solutions are absent, except for some specific open cases.
3-Space In-Flow Theory of Gravity: Boreholes, Blackholes and the Fine Structure Constant
Directory of Open Access Journals (Sweden)
Cahill R. T.
2006-04-01
Full Text Available A theory of 3-space explains the phenomenon of gravity as arising from the time-dependence and inhomogeneity of the differential flow of this 3-space. The emergent theory of gravity has two gravitational constants: G - Newton's constant, and a dimensionless constant alpha. Various experiments and astronomical observations have shown that alpha is the fine structure constant ~1/137. Here we analyse the Greenland Ice Shelf and Nevada Test Site borehole g anomalies, and confirm with increased precision this value of alpha. This and other successful tests of this theory of gravity, including the supermassive black holes in globular clusters and galaxies, and the "dark-matter" effect in spiral galaxies, shows the validity of this theory of gravity. This success implies that the non-relativistic Newtonian gravity was fundamentally flawed from the beginning, and that this flaw was inherited by the relativistic General Relativity theory of gravity.
3-Space In-Flow Theory of Gravity: Boreholes, Blackholes and the Fine Structure Constant
Directory of Open Access Journals (Sweden)
Cahill R. T.
2006-04-01
Full Text Available A theory of 3-space explains the phenomenon of gravity as arising from the time-dependence and inhomogeneity of the differential flow of this 3-space. The emergent theory of gravity has two gravitational constants: GN — Newton’s constant, and a dimensionless constant α. Various experiments and astronomical observations have shown that α is the fine structure constant ≈ 1/137. Here we analyse the Greenland Ice Shelf and Nevada Test Site borehole g anomalies, and confirm with increased precision this value of α. This and other successful tests of this theory of gravity, including the supermassive black holes in globular clusters and galaxies, and the “dark-matter” effect in spiral galaxies, shows the validity of this theory of gravity. This success implies that the non-relativistic Newtonian gravity was fundamentally flawed from the beginning, and that this flaw was inherited by the relativistic General Relativity theory of gravity.
Generalized Supersymmetric Perturbation Theory
Institute of Scientific and Technical Information of China (English)
B. G(o)n(ǖ)l
2004-01-01
@@ Using the basic ingredient of supersymmetry, a simple alternative approach is developed to perturbation theory in one-dimensional non-relativistic quantum mechanics. The formulae for the energy shifts and wavefunctions do not involve tedious calculations which appear in the available perturbation theories. The model applicable in the same form to both the ground state and excited bound states, unlike the recently introduced supersymmetric perturbation technique which, together with other approaches based on logarithmic perturbation theory, are involved within the more general framework of the present formalism.
Noncommutative gravity and quantum field theory on noncummutative curved spacetimes
Energy Technology Data Exchange (ETDEWEB)
Schenkel, Alexander
2011-10-24
noncommutative quantum field theory at short distances, i.e. in the ultraviolet. In the third part we develop elements of a more powerful, albeit more abstract, mathematical approach to noncommutative gravity. The goal is to better understand global aspects of homomorphisms between and connections on noncommutative vector bundles, which are fundamental objects in the mathematical description of noncommutative gravity. We prove that all homomorphisms and connections of the deformed theory can be obtained by applying a quantization isomorphism to undeformed homomorphisms and connections. The extension of homomorphisms and connections to tensor products of modules is clarified, and as a consequence we are able to add tensor fields of arbitrary type to the noncommutative gravity theory of Wess et al. As a nontrivial application of the new mathematical formalism we extend our studies of exact noncommutative gravity solutions to more general deformations.
Quasilocal quantities for GR and other gravity theories
Chen, C.M.; Nester, J. M.
1998-01-01
From a covariant Hamiltonian formulation, by using symplectic ideas, we obtain certain covariant boundary expressions for the quasilocal quantities of general relativity and other geometric gravity theories. The contribution from each of the independent dynamic geometric variables (the frame, metric or connection) has two possible covariant forms associated with the selected type of boundary condition. The quasilocal expressions also depend on a reference value for each dynamic variable and a...
Extreme neutron stars from Extended Theories of Gravity
Energy Technology Data Exchange (ETDEWEB)
Astashenok, Artyom V. [I. Kant Baltic Federal University, Institute of Physics and Technology, Nevskogo st. 14, Kaliningrad, 236041 (Russian Federation); Capozziello, Salvatore [Dipartimento di Fisica, Università di Napoli ' ' Federico II' ' , Via Cinthia, 9, Napoli, I-80126 Italy (Italy); Odintsov, Sergei D., E-mail: artyom.art@gmail.com, E-mail: capozziello@na.infn.it, E-mail: odintsov@ieec.uab.es [Instituciò Catalana de Recerca i Estudis Avançats (ICREA), Barcelona (Spain)
2015-01-01
We discuss neutron stars with strong magnetic mean fields in the framework of Extended Theories of Gravity. In particular, we take into account models derived from f(R) and f(G) extensions of General Relativity where functions of the Ricci curvature invariant R and the Gauss-Bonnet invariant G are respectively considered. Dense matter in magnetic mean field, generated by magnetic properties of particles, is described by assuming a model with three meson fields and baryons octet. As result, the considerable increasing of maximal mass of neutron stars can be achieved by cubic corrections in f(R) gravity. In principle, massive stars with M > 4M{sub ☉} can be obtained. On the other hand, stable stars with high strangeness fraction (with central densities ρ{sub c} ∼ 1.5–2.0 GeV/fm{sup 3}) are possible considering quadratic corrections of f(G) gravity. The magnetic field strength in the star center is of order 6–8 × 10{sup 18} G. In general, we can say that other branches of massive neutron stars are possible considering the extra pressure contributions coming from gravity extensions. Such a feature can constitute both a probe for alternative theories and a way out to address anomalous self-gravitating compact systems.
Cosmological Issues in $F(T)$ Gravity Theory
Bamba, Kazuharu
2015-01-01
We review recent developments on cosmology in extended teleparallel gravity, called "$F(T)$ gravity" with $T$ the torsion scalar in teleparallelism. We explore various cosmological aspects of $F(T)$ gravity including the evolution of the equation of state for the universe, finite-time future singularities, thermodynamics, and four-dimensional effective $F(T)$ gravity theories coming from the higher-dimensional Kaluza-Klein (KK) and Randall-Sundrum (RS) theories.
A general theory of linear cosmological perturbations: bimetric theories
Lagos, Macarena
2016-01-01
We implement the method developed in [1] to construct the most general parametrised action for linear cosmological perturbations of bimetric theories of gravity. Specifically, we consider perturbations around a homogeneous and isotropic background, and identify the complete form of the action invariant under diffeomorphism transformations, as well as the number of free parameters characterising this cosmological class of theories. We discuss, in detail, the case without derivative interactions, and compare our results with those found in massive bigravity.
National Research Council Canada - National Science Library
de Rham, Claudia
2014-01-01
We review recent progress in massive gravity. We start by showing how different theories of massive gravity emerge from a higher-dimensional theory of general relativity, leading to the Dvali–Gabadadze–Porrati model (DGP...
Generalized Galilean Algebras and Newtonian Gravity
Albornoz, N L González; Salgado, P; Salgado, S
2016-01-01
The non-relativistic versions of the generalized Poincar\\'{e} algebras and generalized $AdS$-Lorentz algebras are obtained. This non-relativistic algebras are called, generalized Galilean algebras type I and type II and denoted by $\\mathcal{G}\\mathfrak{B}_{n}$ and $\\mathcal{G}\\mathfrak{L}_{_{n}}$ respectively. Using a generalized In\\"{o}n\\"{u}--Wigner contraction procedure we find that the generalized Galilean algebras type I can be obtained from the generalized Galilean algebras type II. The $S$-expansion procedure allows us to find the $\\mathcal{G}\\mathfrak{B}_{_{5}}$ algebra from the Newton--Hooke algebra with central extension. The procedure developed in Ref. \\cite{newton} allow us to show that the non-relativistic limit of the five dimensional Einstein--Chern--Simons gravity is given by a modified version of the Poisson equation. The modification could be compatible with the effects of Dark Matter, which leads us to think that Dark Matter can be interpreted as a non-relativistic limit of Dark Energy.
A new quasidilaton theory of massive gravity
Mukohyama, Shinji
2014-01-01
We present a new quasidilaton theory of Poincare invariant massive gravity, based on the recently proposed framework of matter coupling that makes it possible for the kinetic energy of the quasidilaton scalar to couple to both physical and fiducial metrics simultaneously. We find a scaling-type exact solution that expresses a self-accelerating de Sitter universe, and then analyze linear perturbations around it. It is shown that in a range of parameters all physical degrees of freedom have non-vanishing quadratic kinetic terms and are stable in the subhorizon limit, while the effective Newton's constant for the background is kept positive.
Hyperbolicity of Scalar Tensor Theories of Gravity
Salgado, Marcelo; Alcubierre, Miguel; Núñez, Dario
2008-01-01
Two first order strongly hyperbolic formulations of scalar tensor theories of gravity (STT) allowing non-minimal couplings (Jordan frame) are presented along the lines of the 3+1 decomposition of spacetime. One is based on the Bona-Masso formulation while the other one employs a conformal decomposition similar to that of Baumgarte-Shapiro-Shibata-Nakamura. A modified Bona-Masso slicing condition adapted to the STT is proposed for the analysis. This study confirms that STT posses a well posed Cauchy problem even when formulated in the Jordan frame.
Cosmological Model Based on Gauge Theory of Gravity
Institute of Scientific and Technical Information of China (English)
WU Ning
2005-01-01
A cosmological model based on gauge theory of gravity is proposed in this paper. Combining cosmological principle and field equation of gravitational gauge field, dynamical equations of the scale factor R(t) of our universe can be obtained. This set of equations has three different solutions. A prediction of the present model is that, if the energy density of the universe is not zero and the universe is expanding, the universe must be space-flat, the total energy density must be the critical density ρc of the universe. For space-flat case, this model gives the same solution as that of the Friedmann model. In other words, though they have different dynamics of gravitational interactions, general relativity and gauge theory of gravity give the same cosmological model.
Vector theory of gravity: solution of dark energy problem
Svidzinsky, Anatoly A
2015-01-01
We propose an alternative classical theory of gravity which assumes that background geometry of the Universe is fixed four dimensional Euclidean space and gravity is a vector field $A_{k}$ in this space which breaks the Euclidean symmetry. Direction of $A_{k}$ gives the time coordinate, while perpendicular directions are spatial coordinates. Vector gravitational field is coupled to matter universally and minimally through the equivalent metric $f_{ik}$ which is a functional of $A_{k}$. We show that such assumptions yield a unique theory of gravity, it is free of black holes and to the best of our knowledge it passes all available tests. For cosmology our theory predicts the same evolution of the Universe as general relativity with cosmological constant and zero spatial curvature. However, the present theory provides explanation of the dark energy as energy of gravitational field induced by the Universe expansion and yields, with no free parameters, the value of $\\Omega _{\\Lambda }=2/3\\approx 0.67$ which agree...
Limitations of cosmography in extended theories of gravity
de la Cruz-Dombriz, Alvaro
2016-01-01
The cosmographic approach, which only relies upon the homogeneity and isotropy of the Universe on large scales, has become an essential tool in dealing with an increasing number of theoretical possibilities for explaining the late-time acceleration of the Universe, ranging from Modified Gravity theories to Dark Energy alternatives passing from testing the cosmological concordance Lambda-CDM model. Despite its generality, we show that this method has a number of shortcomings when trying to adequately reconstruct theories with higher-order derivatives in either the gravitational or the matter sector. Herein some paradigmatic examples of such an inability, explanations of the limitations and prospective cures will be presented.
Massive gravitons from Extended Gravity to Effective Field Theories
Capozziello, Salvatore; Paolella, Mariacristina; Ricciardi, Giulia
2013-01-01
Massive gravitons in effective field theories can be recovered by extending General Relativity and taking into account generic functions of the curvature invariants not necessarily linear in the Ricci scalar R. In particular, adopting the minimal extension of f(R) gravity, an effective field theory with a massive state is straightforwardly recovered. This approach allows to evade shortcomings like ghosts and discontinuities if a suitable choice of expansion parameters is performed. We show that the massive state can be identified with a massive graviton.
Holographical aspects of dyonic black holes: Massive gravity generalization
Hendi, S H; Panahiyan, S
2016-01-01
The content of this paper includes studying holographical and thermodynamical aspects of dyonic black holes in the presence of massive gravity. For the first part of paper, the thermodynamical properties of the bulk which includes black holes are studied. The main focus is on critical behavior. It will be shown that the existence of massive gravitons introduces remnant for temperature for evaporation of black holes, van der Waals phase transition for non-spherical black holes and etc. The consistency of different thermodynamical approaches toward critical behavior of the black holes is proven and the physical properties near to the region of thermal instability are given. Next part of paper studies holographical aspects of the boundary theory. Magnetization and susceptibility of the boundary are extracted and the conditions for having diamagnetic and paramagnetic behaviors are investigated. It will be shown that generalization to massive gravity results into the existences of diamagnetic/paramagnetic phases i...
Cosmology in generalized Proca theories
De Felice, Antonio; Heisenberg, Lavinia; Kase, Ryotaro; Mukohyama, Shinji; Tsujikawa, Shinji; Zhang, Ying-li
2016-06-01
We consider a massive vector field with derivative interactions that propagates only the 3 desired polarizations (besides two tensor polarizations from gravity) with second-order equations of motion in curved space-time. The cosmological implications of such generalized Proca theories are investigated for both the background and the linear perturbation by taking into account the Lagrangian up to quintic order. In the presence of a matter fluid with a temporal component of the vector field, we derive the background equations of motion and show the existence of de Sitter solutions relevant to the late-time cosmic acceleration. We also obtain conditions for the absence of ghosts and Laplacian instabilities of tensor, vector, and scalar perturbations in the small-scale limit. Our results are applied to concrete examples of the general functions in the theory, which encompass vector Galileons as a specific case. In such examples, we show that the de Sitter fixed point is always a stable attractor and study viable parameter spaces in which the no-ghost and stability conditions are satisfied during the cosmic expansion history.
Cosmology in generalized Proca theories
De Felice, Antonio; Kase, Ryotaro; Mukohyama, Shinji; Tsujikawa, Shinji; Zhang, Ying-li
2016-01-01
We consider a massive vector field with derivative interactions that propagates only the 3 desired polarizations (besides two tensor polarizations from gravity) with second-order equations of motion in curved space-time. The cosmological implications of such generalized Proca theories are investigated for both the background and the linear perturbation by taking into account the Lagrangian up to quintic order. In the presence of a matter fluid with a temporal component of the vector field, we derive the background equations of motion and show the existence of de Sitter solutions relevant to the late-time cosmic acceleration. We also obtain conditions for the absence of ghosts and Laplacian instabilities of tensor, vector, and scalar perturbations in the small-scale limit. Our results are applied to concrete examples of the general functions in the theory, which encompass vector Galileons as a specific case. In such examples, we show that the de Sitter fixed point is always a stable attractor and study viable ...
Phenomenology in minimal theory of massive gravity
De Felice, Antonio
2015-01-01
We investigate the minimal theory of massive gravity (MTMG) recently introduced. After reviewing the original construction based on its Hamiltonian in the vielbein formalism, we reformulate it in terms of its Lagrangian in both the vielbein and the metric formalisms. It then becomes obvious that, unlike previous attempts in the literature, not only the potential but also the kinetic structure of the action is modified from the de Rham-Gabadadze-Tolley (dRGT) massive gravity theory. We confirm that the number of physical degrees of freedom in MTMG is two at fully nonlinear level. This proves the absence of various possible pathologies such as superluminality, acausality and strong coupling. Afterwards, we discuss the phenomenology of MTMG in the presence of a dust fluid. We find that on a flat homogeneous and isotropic background we have two branches. One of them (self-accelerating branch) naturally leads to acceleration without the genuine cosmological constant or dark energy. For this branch both the scalar ...
f(R) Gravity and Chameleon Theories
Brax, Philippe; Davis, Anne-Christine; Shaw, Douglas J
2008-01-01
We analyse f(R) modifications of Einstein's gravity as dark energy models in the light of their connection with chameleon theories. Formulated as scalar-tensor theories, the f(R) theories imply the existence of a strong coupling of the scalar field to matter. This would violate all experimental gravitational tests on deviations from Newton's law. Fortunately, the existence of a matter dependent mass and a thin shell effect allows one to alleviate these constraints. The thin shell condition also implies strong restrictions on the cosmological dynamics of the f(R) theories. As a consequence, we find that the equation of state of dark energy in the recent past is constrained to be extremely close to -1. We also examine the potential effects of f(R) theories in the context of the Eot-wash experiments. We show that the requirement of a thin shell for the test bodies is not enough to guarantee a null result on deviations from Newton's law. The constraints which we deduce also forbid any measurable deviation of the ...
Evolving black hole horizons in General Relativity and alternative gravity
Faraoni, Valerio
2013-01-01
From the microscopic point of view, realistic black holes are time-dependent and the teleological concept of event horizon fails. At present, the apparent or the trapping horizon seem its best replacements in various areas of black hole physics. We discuss the known phenomenology of apparent and trapping horizons for analytical solutions of General Relativity and alternative theories of gravity. These specific examples (we focus on spherically symmetric inhomogeneities in a background cosmological spacetime) may be useful as toy models for research on various aspects of black hole physics.
Towards Nonperturbation Theory of Emergent Gravity
Kar, Supriya
2016-01-01
We investigate an emergent gravity in $(4+1)$ dimensions underlying a geometric torsion ${\\cal H}_3$ in $1.5$ order formulation. We show that an emergent pair-symmetric $4$th order curvature tensor underlying a NS field theory governs a torsion free geometry and is identified as the Riemann type tensor. Interestingly a pair anti-symmetric $4$th order tensor is shown to incorporate a dynamical correction underlying a ${\\cal H}_3$ gauge potential and is identified with a non-perturbative correction. The non-perturbative term in the emergent action is shown to be described by a $U(1)$ gauge invariant ${\\cal F}_4$ in a second order theory underlying an onshell ${\\cal H}_3$ in a first order. A complete emergent theory is elegantly described with an axion, and hence a quintessence, coupling to the Riemann type geometries. The curvatures are appropriately worked out to obtain a $12D$ emergent $F$ theory. Further investigation reveals that a pair of $(M{\\bar M})_{10}$-brane are created across an event horizon. We obt...
Testing Alternative Theories of Gravity using LISA
Will, Clifford M
2004-01-01
We investigate the possible bounds which could be placed on alternative theories of gravity using gravitational wave detection from inspiralling compact binaries with the proposed LISA space interferometer. Specifically, we estimate lower bounds on the coupling parameter \\omega of scalar-tensor theories of the Brans-Dicke type and on the Compton wavelength of the graviton \\lambda_g in hypothetical massive graviton theories. In these theories, modifications of the gravitational radiation damping formulae or of the propagation of the waves translate into a change in the phase evolution of the observed gravitational waveform. We obtain the bounds through the technique of matched filtering, employing the LISA Sensitivity Curve Generator (SCG), available online. For a neutron star inspiralling into a 10^3 M_sun black hole in the Virgo Cluster, in a two-year integration, we find a lower bound \\omega > 3 * 10^5. For lower-mass black holes, the bound could be as large as 2 * 10^6. The bound is independent of LISA arm...
The approach to gravity as a theory of embedded surface
Sheykin, A A
2014-01-01
We study the approach to gravity in which our curved spacetime is considered as a surface in a flat ambient space of higher dimension (the embedding theory). The dynamical variable in this theory is not a metric but an embedding function. The Euler-Lagrange equations for this theory (Regge-Teitelboim equations) are more general than the Einstein equations, and admit "extra solutions" which do not correspond to any Einsteinian metric. The Regge-Teitelboim equations can be explicitly analyzed for the solutions with high symmetry. We show that symmetric embeddings of a static spherically symmetric asymptotically flat metrics in a 6-dimensional ambient space do not admit extra solutions of the vacuum Regge-Teitelboim equations. Therefore in the embedding theory the solutions with such properties correspond to the exterior Schwarzchild metric.
General Theories of Regulation
Hertog, J.A. den
1999-01-01
This chapter makes a distinction between three types of theories of regulation: public interest theories, the Chicago theory of regulation and the public choice theories. The Chicago theory is mainly directed at the explanation of economic regulation; public interest theories and public choice theor
Testing gravity theories using tensor perturbations
Lin, Weikang
2016-01-01
Primordial gravitational waves constitute a promising probe of the very-early universe and the laws of gravity. We study changes to tensor mode perturbations that can arise in various proposed modified gravity (MG) theories. These include additional friction effects, non-standard dispersion relations involving a massive graviton, a modified speed, and a small-scale modification. We introduce a physically-motivated parameterization of these effects and use current available data to obtain exclusion regions in the parameter spaces. Taking into account the foreground subtraction, we then perform a forecast analysis focusing on the tensor mode MG parameters as constrained by the future experiments COrE, Stage-IV and PIXIE. For a fiducial value of the tensor-to-scalar ratio r=0.01, we find that an additional friction of 3.5-4.5% compared to GR will be detected at $3\\sigma$ by these experiments while a decrease in friction will be more difficult to detect. The speed of gravitational waves needs to be 5-15% differen...
Application of linear inverse theory to borehole gravity data
Energy Technology Data Exchange (ETDEWEB)
Burkhard, N.R.
1991-09-01
Traditional borehole gravity interpretations are based upon an earth model which assumes horizontal, laterally infinite, uniformly thick, and constant density layers. I apply discrete stabilized linear inverse theory to determine the density distribution directly from borehole gravity observations that have been corrected for drift, tide, and terrain. The stabilization is the result of including a priori data about the free-air gradient and the density structure in the inversion process. The discrete generalized linear inverse approach enables one to solve for a density distribution using all of the borehole gravity data. Moreover, the data need not be free-air corrected. An important feature of the approach is that density estimates are not required to be density averages between adjacent borehole gravity observations as in the traditional method. This approach further permits the explicit incorporation of independent density information from gamma-gamma logging tools or laboratory core measurements. Finally, explicit linear constraints upon the density and/or free-air gradient can also be handled. The non-uniqueness of the density structure determined by the inversion process is represented in a resolution matrix. 12 refs., 11 figs.
Chakravarty, Girish Kumar; Mohanty, Subhendra
2016-01-01
Many extensions of Einstein's theory of gravity have been studied and proposed with various motivations like the quest for a quantum theory of gravity to extensions of anomalies in observations at the solar system, galactic and cosmological scales. These extensions include adding higher powers of Ricci curvature $R$, coupling the Ricci curvature with scalar fields and generalized functions of $R$. In addition when viewed from the perspective of Supergravity (SUGRA) many of these theories may originate from the same SUGRA theory interpreted in different frames. SUGRA therefore serves as a good framework for organizing and generalizing theories of gravity beyond General Relativity. All these theories when applied to inflation (a rapid expansion of early Universe in which primordial gravitational waves might be generated and might still be detectable by the imprint they left or by the ripples that persist today) can have distinct signatures in the Cosmic Microwave Background radiation temperature and polarizatio...
Matrix models, noncommutative gauge theory and emergent gravity
Energy Technology Data Exchange (ETDEWEB)
Steinacker, Harold [Fakultaet fuer Physik, Universitaet Wien (Austria)
2009-07-01
Matrix Models of Yang-Mills type are studied with focus on the effective geometry. It is shown that SU(n) gauge fields and matter on general 4-dimensional noncommutative branes couple to an effective metric, leading to emergent gravity. The effective metric is reminiscent of the open string metric, and depends on the dynamical Poisson structure. Covariant equations of motion are derived, which are protected from quantum corrections due to an underlying Noether theorem. The quantization is discussed qualitatively, which singles out the IKKT model as a candidate for a quantum theory of gravity coupled to matter. UV/IR mixing plays a central role. A mechanism for avoiding the cosmological constant problem is exhibited.
Dynamical 3-Space Gravity Theory: Effects on Polytropic Solar Models
Directory of Open Access Journals (Sweden)
Cahill R. T.
2011-01-01
Full Text Available Numerous experiments and observations have confirmed the existence of a dynamical 3-space, detectable directly by light-speed anisotropy experiments, and indirectly by means of novel gravitational effects, such as bore hole g-anomalies, predictable black hole masses, flat spiral-galaxy rotation curves, and the expansion of the universe, all without dark matter and dark energy. The dynamics for this 3-space follows from a unique generalisation of Newtonian gravity, once that is cast into a velocity formalism. This new theory of gravity is applied to the solar model of the sun to compute new density, pressure and temperature profiles, using polytrope modelling of the equation of state for the matter. These results should be applied to a re-analysis of solar neutrino production, and to stellar evolution in general.
Dynamical 3-Space Gravity Theory: Effects on Polytropic Solar Models
Directory of Open Access Journals (Sweden)
May R. D.
2011-01-01
Full Text Available Numerous experiments and observations have confirmed the existence of a dynamical 3-space, detectable directly by light-speed anisotropy experiments, and indirectly by means of novel gravitational effects, such as bore hole g anomalies, predictable black hole masses, flat spiral-galaxy rotation curves, and the expansion of the universe, all without dark matter and dark energy. The dynamics for this 3-space follows from a unique generalisation of Newtonian gravity, once that is cast into a velocity formalism. This new theory of gravity is applied to the solar model of the sun to compute new density, pressure and temperature profiles, using polytrope modelling of the equation of state for the matter. These results should be applied to a re-analysis of solar neutrino production, and to stellar evolution in general.
Quantum Gravity from the Point of View of Locally Covariant Quantum Field Theory
Brunetti, Romeo; Fredenhagen, Klaus; Rejzner, Katarzyna
2016-08-01
We construct perturbative quantum gravity in a generally covariant way. In particular our construction is background independent. It is based on the locally covariant approach to quantum field theory and the renormalized Batalin-Vilkovisky formalism. We do not touch the problem of nonrenormalizability and interpret the theory as an effective theory at large length scales.
Probing Modified Gravity Theories with ISW and CMB Lensing
Munshi, D; Renzi, A; Heavens, A; Coles, P
2014-01-01
The imprint of the cross-correlation of the Integrated Sachs-Wolfe effect (ISW) and lensing of the cosmic microwave background (CMB) radiation has recently been detected in the bispectrum of temperature maps. In this paper, we use the optimised skew-spectrum as well as skew-spectra associated with Minkowski Functionals (MFs) to test the possibility of using this signal to detect deviations in the theory of gravity away from General Relativity (GR). We find that the although both statistics can put constraints on modified gravity, the optimised skew-spectra are especially sensitive to the parameter $\\rB_0$ that denotes the the {\\em Compton wavelength} of the scalaron at the present epoch, and both can be used to put stringent constraints on any departure from GR, or pinpoint any systematics in the data. We investigate three modified gravity theories, namely: the Post-Parametrised Friedmanian (PPF) formalism; the Hu-Sawicki (HS) model; and the Bertschinger-Zukin (BZ) formalism. Employing a likelihood analysis f...
Cosmology of the proxy theory to massive gravity
Heisenberg, Lavinia; Yamamoto, Kazuhiro
2014-01-01
In this paper, we scrutinize very closely the cosmology in the proxy theory to massive gravity obtained in Phys. Rev. D84 (2011) 043503. This proxy theory was constructed by covariantizing the decoupling limit Lagrangian of massive gravity and represents a subclass of Horndeski scalar-tensor theory. Thus, this covariantization unifies two important classes of modified gravity theories, namely massive gravity and Horndeski theories. We go beyond the regime which was studied in Phys. Rev. D84 (2011) 043503 and show that the theory does not admit any homogeneous and isotropic self-accelerated solutions. We illustrate that the only attractor solution is flat Minkowski solution, hence this theory is less appealing as a dark energy model. We also show that the absence of de Sitter solutions is tightly related to the presence of shift symmetry breaking interactions.
Cosmology of the proxy theory to massive gravity
Heisenberg, Lavinia; Kimura, Rampei; Yamamoto, Kazuhiro
2014-05-01
In this paper, we scrutinize very closely the cosmology in the proxy theory to massive gravity obtained in de Rham and Heisenberg [Phys. Rev. D 84, 043503 (2011)]. This proxy theory was constructed by covariantizing the decoupling limit Lagrangian of massive gravity, and it represents a subclass of Horndeski scalar-tensor theory. Thus, this covariantization unifies two important classes of modified gravity theories, namely, massive gravity and Horndeski theories. We go beyond the regime which was studied in de Rham and Heisenberg [Phys. Rev. D 84, 043503 (2011)] and show that the theory does not admit any homogeneous and isotropic self-accelerated solutions. We illustrate that the only attractor solution is the flat Minkowski solution; hence, this theory is less appealing as a dark energy model. We also show that the absence of de Sitter solutions is tightly related to the presence of shift symmetry breaking interactions.
Rationale for a Correlated Worldline Theory of Quantum Gravity
Stamp, P C E
2015-01-01
It is argued that gravity should cause a breakdown of quantum mechanics, at low energies, accessible to table-top experiments. It is then shown that one can formulate a theory of quantum gravity in which gravitational correlations exist between worldline or worldsheet paths, for the particle or field of interest. Using a generalized equivalence principle, one can give a unique form for the correlators, yielding a theory with no adjustable parameters. A key feature of the theory is the "bunching" of quantum trajectories caused by the gravitational correlations - this is {\\it not} a decoherence or a "collapse" mechanism. This bunching causes a breakdown of the superposition principle for large masses, with a very rapid crossover to classical behaviour at an energy scale which depends on the physical structure of the object. Formal details, and applications of the theory, are kept to a minimum in this paper; but we show how physical quantities can be calculated, and give a detailed discussion of the dynamics of ...
Reissner Nordstrom Metric in Unimodular Theory of Gravity
Chaturvedi, Pankaj; Singh, Dharm Veer
2016-01-01
We study the modified Reissner Nordstrom metric in the unimodular gravity. So far the spherically symmetric Einstein field equation in unimodular gravity has been studied in the absence of any source. We consider static electric and magnetic charge as source. We solve for Maxwell equations in unimodular gravitational background. We show that in unimodular gravity the electromagnetic field strength tensor is modified. We also show that the solution in unimodular gravity differs from the usual R-N metric in Einstein gravity with some corrections. We further study the thermodynamical properties of the R-N black-hole solution in this theory.
Aspects of Neutrino Oscillation in Alternative Gravity Theories
Chakraborty, Sumanta
2015-01-01
Neutrino spin and flavour oscillation in curved spacetime have been studied for the most general static spherically symmetric configuration. Using the symmetry properties we have derived spin oscillation frequency for neutrino moving along a geodesic or in a circular orbit. Starting from the expression of neutrino spin oscillation frequency we have shown that even in this general context, in high energy limit the spin oscillation frequency for neutrino moving along circular orbit vanishes. This finally lends itself to non-zero probability of neutrino helicity flip. While for neutrino flavour oscillation we have derived general results for oscillation phase, which subsequently have been applied to different gravity theories. These include dilaton field coupled to Maxwell field tensor, generalization of Schwarzschild solution by introduction of quadratic curvature terms of all possible form to the Einstein-Hilbert action and finally regular black hole solutions. In all these cases using the solar neutrino oscil...
Ni, W.-T.
1972-01-01
Metric theories of gravity are compiled and classified according to the types of gravitational fields they contain, and the modes of interaction among those fields. The gravitation theories considered are classified as (1) general relativity, (2) scalar-tensor theories, (3) conformally flat theories, and (4) stratified theories with conformally flat space slices. The post-Newtonian limit of each theory is constructed and its Parametrized Post-Newtonian (PPN) values are obtained by comparing it with Will's version of the formalism. Results obtained here, when combined with experimental data and with recent work by Nordtvedt and Will and by Ni, show that, of all theories thus far examined by our group, the only currently viable ones are general relativity, the Bergmann-Wagoner scalar-tensor theory and its special cases (Nordtvedt; Brans-Dicke-Jordan), and a recent, new vector-tensor theory by Nordtvedt, Hellings, and Will.
Nonlinear electrodynamics coupled to teleparallel theory of gravity
Institute of Scientific and Technical Information of China (English)
Gamal G. L. Nashed
2011-01-01
Using nonlinear electrodynamics coupled to teleparallel theory of gravity, regular charged spherically symmetric solutions are obtained. The nonlinear theory is reduced to the Maxwell one in the weak limit and the solutions correspond to charged spacetimes. One of the obtained solutions contains an arbitrary function which we call general solution since we can generate from it the other solutions. The metric associated with these spacetimes is the same, i.e., regular charged static spherically symmetric black hole. In calculating the energy content of the general solution using the gravitational energy-momentum within the framework of the teleparallel geometry, we find that the resulting form depends on the arbitrary function. Using the regularized expression of the gravitational energy-momentum we obtain the value of energy.
Gravity, Gauge Theories and Geometric Algebra
Lasenby, A; Gull, S F; Lasenby, Anthony; Doran, Chris; Gull, Stephen
1998-01-01
A new gauge theory of gravity is presented. The theory is constructed in a flat background spacetime and employs gauge fields to ensure that all relations between physical quantities are independent of the positions and orientations of the matter fields. In this manner all properties of the background spacetime are removed from physics, and what remains are a set of `intrinsic' relations between physical fields. The properties of the gravitational gauge fields are derived from both classical and quantum viewpoints. Field equations are then derived from an action principle, and consistency with the minimal coupling procedure selects an action that is unique up to the possible inclusion of a cosmological constant. This in turn singles out a unique form of spin-torsion interaction. A new method for solving the field equations is outlined and applied to the case of a time-dependent, spherically-symmetric perfect fluid. A gauge is found which reduces the physics to a set of essentially Newtonian equations. These e...
String Field Theory from Quantum Gravity
Crane, Louis
2012-01-01
Recent work on neutrino oscillations suggests that the three generations of fermions in the standard model are related by representations of the finite group A(4), the group of symmetries of the tetrahedron. Motivated by this, we explore models which extend the EPRL model for quantum gravity by coupling it to a bosonic quantum field of representations of A(4). This coupling is possible because the representation category of A(4) is a module category over the representation categories used to construct the EPRL model. The vertex operators which interchange vacua in the resulting quantum field theory reproduce the bosons and fermions of the standard model, up to issues of symmetry breaking which we do not resolve. We are led to the hypothesis that physical particles in nature represent vacuum changing operators on a sea of invisible excitations which are only observable in the A(4) representation labels which govern the horizontal symmetry revealed in neutrino oscillations. The quantum field theory of the A(4) ...
Extreme neutron stars from Extended Theories of Gravity
Astashenok, Artyom V; Odintsov, Sergei D
2014-01-01
We discuss neutron stars with strong magnetic mean fields in the framework of Extended Theories of Gravity. In particular, we take into account models derived from $f(R)$ and $f(\\cal G)$ extensions of General Relativity where functions of the Ricci curvature invariant $R$ and the Gauss-Bonnet invariant ${\\cal G}$ are respectively considered. Dense matter in magnetic mean field, generated by magnetic properties of particles, is described by assuming a model with three meson fields and baryons octet. As result, the considerable increasing of maximal mass of neutron stars can be achieved by cubic corrections in $f(R)$ gravity. In principle, massive stars with $M> 4 M_{\\odot}$ can be obtained. On the other hand, stable stars with high strangeness fraction (with central densities $\\rho_{c}\\sim 1.5-2.0$ GeV/fm$^{3}$) are possible considering quadratic corrections of $f(\\cal {G})$ gravity. The magnetic field strength in the star center is of order $6-8\\times 10^{18}$ G. In general, we can say that other branches of ...
Equilibrium and stability of relativistic stars in extended theories of gravity
Energy Technology Data Exchange (ETDEWEB)
Wojnar, Aneta [Maria Curie-Sklodowska University, Institute of Physics, Lublin (Poland); Univ. di Monte S. Angelo, Napoli (Italy); Universita' di Napoli Federico II, Complesso Universitario di Monte S. Angelo, Dipartimento di Fisica ' ' E. Pancini' ' , Naples (Italy); INFN, Napoli (Italy); Velten, Hermano [Universidade Federal do Espirito Santo (UFES), Vitoria (Brazil)
2016-12-15
We study static, spherically symmetric equilibrium configurations in extended theories of gravity (ETG) following the notation introduced by Capozziello et al. We calculate the differential equations for the stellar structure in such theories in a very generic form i.e., the Tolman-Oppenheimer-Volkoff generalization for any ETG is introduced. Stability analysis is also investigated with special focus on the particular example of scalar-tensor gravity. (orig.)
Equilibrium and stability of relativistic stars in extended theories of gravity
Wojnar, Aneta
2016-01-01
We study static, spherically symmetric equilibrium configurations in extended theories of gravity (ETG) following the notation introduced by Capozziello et {\\it al}. We calculate the differential equations for the stellar structure in such theories in a very generic form i.e., the Tolman-Oppenheimer-Volkoff generalization for any ETG is introduced. Stability analysis is also investigated with special focus on the particular example of scalar-tensor gravity.
Gravity as Archimedes' thrust and a bifurcation in that theory
Arminjon, Mayeul
2004-01-01
Euler's interpretation of Newton's gravity (NG) as Archimedes' thrust in a fluid ether is presented in some detail. Then a semi-heuristic mechanism for gravity, close to Euler's, is recalled and compared with the latter. None of these two "gravitational ethers" can obey classical mechanics. This is logical since the ether defines the very reference frame, in which mechanics is defined. This concept is used to build a scalar theory of gravity: NG corresponds to an incompressible ether, a compr...
Gauge theories for gravity on a line
Jackiw, Roman W
1992-01-01
Professor M. C. Polivanov and I met only a few times, during my infrequent visits to the-then Soviet Union in the 1970's and 1980's. His hospitality at the Moscow Steclov Institute made the trips a pleasure, while the scientific environment that he provided made them professionally valuable. But it is the human contact that I remember most vividly and shall now miss after his death. At a time when issues of conscience were both pressing for attention and difficult/dangerous to confront, Professor Polivanov made a deep impression with his quiet but adamant commitment to justice. I can only guess at the satisfaction he must have felt when his goal of gaining freedom for Yuri Orlov was attained, and even more so these days when human rights became defensible in his country; it is regrettable that he cannot now enjoy the future that he strived to attain. One of our joint interests was the Liouville theory,$^{1,\\,2}$ which in turn can be viewed as a model for gravity in two-dimensional space-time. Some recent deve...
Disformal transformations, veiled General Relativity and Mimetic Gravity
Energy Technology Data Exchange (ETDEWEB)
Deruelle, Nathalie [APC, CNRS-Université Paris 7, 75205 Paris CEDEX 13 (France); Rua, Josephine, E-mail: deruelle@ihes.fr, E-mail: rua@cbpf.br [Instituto de Cosmologia, Relatividade e Astrofísica—ICRA/CBPF, Rua Dr. Xavier Sigaud 150, 22290-180 Rio de Janeiro (Brazil)
2014-09-01
In this Note we show that Einstein's equations for gravity are generically invariant under ''disformations''. We also show that the particular subclass when this is not true yields the equations of motion of ''Mimetic Gravity''. Finally we give the ''mimetic'' generalization of the Schwarzschild solution.
Gravity theories, Transverse Doppler and Gravitational Redshifts in Galaxy Clusters
Zhao, Hongsheng; Li, Baojiu
2012-01-01
There is growing interest in testing alternative gravity theories using the subtle Gravitational Redshifts in clusters of galaxies. However, current models all neglect a Transverse Doppler redshift of similar magnitude, and some models are not self-consistent. An equilibrium model would fix the Gravitational and Transverse Doppler velocity shifts to be about 6\\sigma^2/c and 3\\sigma^2/2c in order to fit the observed velocity dispersion \\sigma self-consistently. This result is from the Virial Theorem for a spherical isotropic cluster, and is insensitive to the theory of gravity. In any case, a gravitational redshift signal cannot directly distinguish between the Einsteinian and f(R) gravity theories, because the mass of the cluster dark halo must be treated as an unknown fitting parameter, whose value must vary according to the theory adopted, otherwise the system would be in equilibrium in one gravity theory and out of equilibrium in another.
Einstein's theory of gravity and the problem of missing mass.
Ferreira, Pedro G; Starkman, Glenn D
2009-11-01
The observed matter in the universe accounts for just 5% of the observed gravity. A possible explanation is that Newton's and Einstein's theories of gravity fail where gravity is either weak or enhanced. The modified theory of Newtonian dynamics (MOND) reproduces, without dark matter, spiral-galaxy orbital motions and the relation between luminosity and rotation in galaxies, although not in clusters. Recent extensions of Einstein's theory are theoretically more complete. They inevitably include dark fields that seed structure growth, and they may explain recent weak lensing data. However, the presence of dark fields reduces calculability and comes at the expense of the original MOND premise, that the matter we see is the sole source of gravity. Observational tests of the relic radiation, weak lensing, and the growth of structure may distinguish modified gravity from dark matter.
General proof of the entropy principle for self-gravitating fluid in f ( R) gravity
Fang, Xiongjun; Guo, Minyong; Jing, Jiliang
2016-08-01
The discussions on the connection between gravity and thermodynamics attract much attention recently. We consider a static self-gravitating perfect fluid system in f ( R) gravity, which is an important theory could explain the accelerated expansion of the universe. We first show that the Tolman-Oppenheimer-Volkoff equation of f ( R) theories can be obtained by thermodynamical method in spherical symmetric spacetime. Then we prove that the maximum entropy principle is also valid for f ( R) gravity in general static spacetimes beyond spherical symmetry. The result shows that if the constraint equation is satisfied and the temperature of fluid obeys Tolmans law, the extrema of total entropy implies other components of gravitational equations. Conversely, if f ( R) gravitational equation hold, the total entropy of the fluid should be extremum. Our work suggests a general and solid connection between f ( R) gravity and thermodynamics.
Stability of the Einstein static universe in modified theories of gravity
Boehmer, Christian G.; Hollenstein, Lukas; Lobo, Francisco S. N.; Seahra, Sanjeev S.
2010-01-01
We present a brief overview of the stability analysis of the Einstein static universe in various modified theories of gravity, like f(R) gravity, Gauss-Bonnet or f(G) gravity, and Horava-Lifshitz gravity.
Stability of the Einstein static universe in modified theories of gravity
Boehmer, Christian G.; Hollenstein, Lukas; Lobo, Francisco S. N.; Seahra, Sanjeev S.
2010-01-01
We present a brief overview of the stability analysis of the Einstein static universe in various modified theories of gravity, like f(R) gravity, Gauss-Bonnet or f(G) gravity, and Horava-Lifshitz gravity.
Perturbative quantum gravity in double field theory
Boels, Rutger H.; Horst, Christoph
2016-04-01
We study perturbative general relativity with a two-form and a dilaton using the double field theory formulation which features explicit index factorisation at the Lagrangian level. Explicit checks to known tree level results are performed. In a natural covariant gauge a ghost-like scalar which contributes even at tree level is shown to decouple consistently as required by perturbative unitarity. In addition, a lightcone gauge is explored which bypasses the problem altogether. Using this gauge to study BCFW on-shell recursion, we can show that most of the D-dimensional tree level S-matrix of the theory, including all pure graviton scattering amplitudes, is reproduced by the double field theory. More generally, we argue that the integrand may be reconstructed from its single cuts and provide limited evidence for off-shell cancellations in the Feynman graphs. As a straightforward application of the developed technology double field theory-like expressions for four field string corrections are derived.
Perturbative quantum gravity in double field theory
Boels, Rutger H
2015-01-01
We study perturbative general relativity with a two-form and a dilaton using the double field theory formulation which features explicit index factorisation at the Lagrangian level. Explicit checks to known tree level results are performed. In a natural covariant gauge a ghost-like scalar which contributes even at tree level is shown to decouple consistently as required by perturbative unitarity. In addition, a lightcone gauge is explored which bypasses the problem altogether. Using this gauge to study BCFW on-shell recursion, we can show that most of the D-dimensional tree level S-matrix of the theory, including all pure graviton scattering amplitudes, is reproduced by the double field theory. More generally, we argue that the integrand may be reconstructed from its single cuts and provide limited evidence for off-shell cancellations in the Feynman graphs. As a straightforward application of the developed technology double field theory-like expressions for four field string corrections are derived.
Cosmology from group field theory formalism for quantum gravity.
Gielen, Steffen; Oriti, Daniele; Sindoni, Lorenzo
2013-07-19
We identify a class of condensate states in the group field theory (GFT) formulation of quantum gravity that can be interpreted as macroscopic homogeneous spatial geometries. We then extract the dynamics of such condensate states directly from the fundamental quantum GFT dynamics, following the procedure used in ordinary quantum fluids. The effective dynamics is a nonlinear and nonlocal extension of quantum cosmology. We also show that any GFT model with a kinetic term of Laplacian type gives rise, in a semiclassical (WKB) approximation and in the isotropic case, to a modified Friedmann equation. This is the first concrete, general procedure for extracting an effective cosmological dynamics directly from a fundamental theory of quantum geometry.
Quantum Gravity as a Deformed Topological Quantum Field Theory
Energy Technology Data Exchange (ETDEWEB)
Mikovic, Aleksandar [Departamento de Matematica, Universidade Lusofona de Humanidades e Tecnologias, Av. do Campo Grande, 376, 1749-024 Lisbon (Portugal)
2006-03-01
It is known that the Einstein-Hilbert action with a positive cosmological constant can be represented as a perturbation of the SO(4, 1) BF theory by a symmetry-breaking term quadratic in the B field. Introducing fermionic matter generates additional terms in the action which are polynomial in the tetrads and the spin connection. We describe how to construct the generating functional in the spin foam formalism for a generic BF theory when the sources for the B and the gaugefield are present. This functional can be used to obtain a path integral for General Relativity with matter as a perturbative series whose the lowest order term is a path integral for a topological gravity coupled to matter.
Introduction to Palatini theories of gravity and nonsingular cosmologies
Olmo, Gonzalo J
2013-01-01
These notes are a summary of lectures given at the Instituto de Astronomia of the Universidad Nacional Autonoma de Mexico (UNAM), the Dipartimento di Fisica of the Universita degli studi di Salerno (Italy), and the Instituto de Fisica Corpuscular of the Universitat de Valencia (Spain) during the year 2012. Basic mathematical aspects of Palatini theories of gravity, which are constructed assuming that metric and connection are independent geometrical entities, are briefly introduced and discussed, and followed by a detailed derivation of the field equations of some rather general Lagrangian theories. Applications to the early universe are considered paying special attention to the avoidance of the big bang singularity. The analysis of non-singular cosmologies carried out in arXiv:1005.4136 [gr-qc] is extended to include several perfect fluids.
Bimetric gravity doubly coupled to matter: theory and cosmological implications
Energy Technology Data Exchange (ETDEWEB)
Akrami, Yashar; Koivisto, Tomi S.; Mota, David F.; Sandstad, Marit, E-mail: yashar.akrami@astro.uio.no, E-mail: t.s.koivisto@astro.uio.no, E-mail: d.f.mota@astro.uio.no, E-mail: marit.sandstad@astro.uio.no [Institute of Theoretical Astrophysics, University of Oslo P.O. Box 1029 Blindern, N-0315 Oslo (Norway)
2013-10-01
A ghost-free theory of gravity with two dynamical metrics both coupled to matter is shown to be consistent and viable. Its cosmological implications are studied, and the models, in particular in the context of partially massless gravity, are found to explain the cosmic acceleration without resorting to dark energy.
Warped AdS{sub 3} black holes in higher derivative gravity theories
Energy Technology Data Exchange (ETDEWEB)
Detournay, Stéphane [Université Libre de Bruxelles and International Solvay Institutes,Physique Théorique et Mathématique,Campus Plaine C.P. 231, B-1050 Bruxelles (Belgium); Douxchamps, Laure-Anne [Université Libre de Bruxelles and International Solvay Institutes,Physique Théorique et Mathématique,Campus Plaine C.P. 231, B-1050 Bruxelles (Belgium); Department of Physics, McGill University,Montréal, QC H3A 2T8 (Canada); Ng, Gim Seng [Department of Physics, McGill University,Montréal, QC H3A 2T8 (Canada); Zwikel, Céline [Université Libre de Bruxelles and International Solvay Institutes,Physique Théorique et Mathématique,Campus Plaine C.P. 231, B-1050 Bruxelles (Belgium)
2016-06-06
We consider warped AdS{sub 3} black holes in generic higher derivatives gravity theories in 2+1 dimensions. The asymptotic symmetry group of the phase space containing these black holes is the semi-direct product of a centrally extended Virasoro algebra and an affine u(1) Kac-Moody algebra. Previous works have shown that in some specific theories, the entropy of these black holes agrees with a Cardy-like entropy formula derived for warped conformal field theories. In this paper, we show that this entropy matching continues to hold for the most general higher derivative theories of gravity. We also discuss the existence of phase transitions.
Time and Energy in Gravity Theory
Pestov, I B
2003-01-01
A new concept of internal time (viewed as a scalar temporal field) is introduced which allows one to solve the energy problem in General Relativity. The law of energy conservation means that the total energy density of the full system of interacting fields (including gravitational field) does not vary with time, thus being the first integral of the system. It is demonstrated that direct introduction of the temporal field permits to derive the general covariant four dimensional Maxwell equations for the electric and magnetic fields from the equations of electromagnetic fields considering in General Relativity. It means that the fundamental physical laws are in full correspondence with the essence of time. Theory of time presented here predicts the existence of matter outside the time.
General Relativity As an Aether Theory
Dupre, Maurice J
2010-01-01
Most early twentieth century relativists --- Lorentz, Einstein, Eddington, for examples --- claimed that general relativity was merely a theory of the aether. We shall confirm this claim by deriving the Einstein equations using aether theory. We shall use a combination of Lorentz's and Kelvin's conception of the aether. Our derivation of the Einstein equations will not use the vanishing of the covariant divergence of the stress-energy tensor, but instead equate the Ricci tensor to the sum of the usual stress-energy tensor and a stress-energy tensor for the aether, a tensor based on Kelvin's aether theory. A crucial first step is generalizing the Cartan formalism of Newtonian gravity to allow spatial curvature, as conjectured by Gauss and Riemann.
Gauge Natural Formulation of Conformal Theory of Gravity
Campigotto, M.; Fatibene, L.
2014-01-01
We consider conformal gravity as a gauge natural theory. We study its conservation laws and superpotentials. We also consider the Mannheim and Kazanas spherically symmetric vacuum solution and discuss conserved quantities associated to conformal and diffeomorphism symmetries.
Extended DBI massive gravity with generalized fiducial metric
Energy Technology Data Exchange (ETDEWEB)
Chullaphan, Tossaporn [The Institute for Fundamental Study, Naresuan University,Phitsanulok 65000 (Thailand); Department of Physics, Faculty of Science, Udon Thani Rajabhat University,Udon Thani 41000 (Thailand); Tannukij, Lunchakorn [Department of Physics, Faculty of Science, Mahidol University,Bangkok 10400 (Thailand); Wongjun, Pitayuth [The Institute for Fundamental Study, Naresuan University,Phitsanulok 65000 (Thailand); Thailand Center of Excellence in Physics, Ministry of Education,Bangkok 10400 (Thailand)
2015-06-05
We consider an extended model of DBI massive gravity by generalizing the fiducial metric to be an induced metric on the brane corresponding to a domain wall moving in five-dimensional Schwarzschild-Anti-de Sitter spacetime. The model admits all solutions of FLRW metric including flat, closed and open geometries while the original one does not. The background solutions can be divided into two branches namely self-accelerating branch and normal branch. For the self-accelerating branch, the graviton mass plays the role of cosmological constant to drive the late-time acceleration of the universe. It is found that the number degrees of freedom of gravitational sector is not correct similar to the original DBI massive gravity. There are only two propagating degrees of freedom from tensor modes. For normal branch, we restrict our attention to a particular class of the solutions which provides an accelerated expansion of the universe. It is found that the number of degrees of freedom in the model is correct. However, at least one of them is ghost degree of freedom which always present at small scale implying that the theory is not stable.
Adiabaticity and gravity theory independent conservation laws for cosmological perturbations
Romano, Antonio Enea; Sasaki, Misao
2015-01-01
We carefully study the implications of adiabaticity for the behavior of cosmological perturbations. There are essentially three similar but different definitions of non-adiabaticity: one is appropriate for a thermodynamic fluid $\\delta P_{nad}$, another is for a general matter field $\\delta P_{c,nad}$, and the last one is valid only on superhorizon scales. The first two definitions coincide if $c_s^2=c_w^2$ where $c_s$ is the propagation speed of the perturbation, while $c_w^2=\\dot P/\\dot\\rho$. Assuming the adiabaticity in the general sense, $\\delta P_{c,nad}=0$, we derive a relation between the lapse function in the comoving slicing $A_c$ and $\\delta P_{nad}$ valid for arbitrary matter field in any theory of gravity, by using only momentum conservation. The relation implies that as long as $c_s\
The Cauchy problem of scalar-tensor theories of gravity
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Salgado, Marcelo [Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, Apdo. Postal 70-543 Mexico 04510 DF (Mexico)
2006-07-21
The 3 + 1 formulation of scalar-tensor theories of gravity (STT) is obtained in the physical (Jordan) frame departing from the 4 + 0 covariant field equations. Contrary to common belief (folklore), the new system of ADM-like equations shows that the Cauchy problem of STT is well formulated (in the sense that the whole system of evolution equations is of first order in the time derivative). This is the first step towards a full first-order (in time and space) formulation from which a subsequent hyperbolicity analysis (a well-posedness determination) can be performed. Several gauge (lapse and shift) conditions are considered and implemented for STT. In particular, a generalization of the harmonic gauge for STT allows us to prove the well posedness of the STT using a second-order analysis which is very similar to the one employed in general relativity. Several appendices complement the ideas of the main part of the paper.
On Poincaré gauge theory of gravity, its equations of motion, and Gravity Probe B
Energy Technology Data Exchange (ETDEWEB)
Hehl, Friedrich W., E-mail: hehl@thp.uni-koeln.de [Institute for Theoretical Physics, University of Cologne, 50923 Köln (Germany); Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211 (United States); Obukhov, Yuri N., E-mail: yo@thp.uni-koeln.de [Theoretical Physics Laboratory, Nuclear Safety Institute, Russian Academy of Sciences, B. Tulskaya 52, 115191 Moscow (Russian Federation); Puetzfeld, Dirk, E-mail: dirk.puetzfeld@zarm.uni-bremen.de [ZARM, University of Bremen, Am Fallturm, 28359 Bremen (Germany)
2013-10-30
We discuss the structure of the Poincaré gauge theory of gravity (PG) that can be considered as the standard theory of gravity with torsion. We reconfirm that torsion, in the context of PG, couples only to the elementary particle spin and under no circumstances to the orbital angular momentum of test particles. We conclude that, unfortunately, the investigations of Mao et al. (2007) and March et al. (2011)—who claimed a coupling of torsion to orbital angular momentum, in particular in the context of the Gravity Probe B (GPB) experiment—do not yield any information on torsion.
Generalized Noether symmetry in f(T) gravity
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Mohseni Sadjadi, H., E-mail: mohsenisad@ut.ac.ir [Department of Physics, University of Tehran, P.O.B. 14395-547, Tehran 14399-55961 (Iran, Islamic Republic of)
2012-12-05
We consider modified teleparallel gravity (f(T) gravity), as a framework to explain the present accelerated expansion of the universe. The matter component is assumed to be cold dark matter. To find the explicit form of the function f, we utilize generalized Noether theorem and use generalized vector fields as variational symmetries of the corresponding Lagrangian. We study the cosmological consequences of the obtained results.
Generalized Noether symmetry in f(T) gravity
Sadjadi, H Mohseni
2012-01-01
We consider modified teleparallel gravity, (f(T) gravity), as a framework to explain the present accelerated expansion of the universe. The matter component is assumed to be cold dark matter. To find the explicit form of the function $f$, we utilize generalized Noether theorem and use generalized vector fields as a variational symmetries of the corresponding Lagrangian. We study the cosmological consequences of the obtained results.
Dark energy or modified gravity? An effective field theory approach
Energy Technology Data Exchange (ETDEWEB)
Bloomfield, Jolyon; Flanagan, Éanna É. [Center for Radiophysics and Space Research, Cornell University, Ithaca, NY 14853 (United States); Park, Minjoon [Department of Physics, University of Massachusetts, Amherst, MA 01003 (United States); Watson, Scott, E-mail: jkb84@cornell.edu, E-mail: eef3@cornell.edu, E-mail: minjoonp@physics.umass.edu, E-mail: gswatson@syr.edu [Department of Physics, Syracuse University, Syracuse, NY 13244 (United States)
2013-08-01
We take an Effective Field Theory (EFT) approach to unifying existing proposals for the origin of cosmic acceleration and its connection to cosmological observations. Building on earlier work where EFT methods were used with observations to constrain the background evolution, we extend this program to the level of the EFT of the cosmological perturbations — following the example from the EFT of Inflation. Within this framework, we construct the general theory around an assumed background which will typically be chosen to mimic ΛCDM, and identify the parameters of interest for constraining dark energy and modified gravity models with observations. We discuss the similarities to the EFT of Inflation, but we also identify a number of subtleties including the relationship between the scalar perturbations and the Goldstone boson of the spontaneously broken time translations. We present formulae that relate the parameters of the fundamental Lagrangian to the speed of sound, anisotropic shear stress, effective Newtonian constant, and Caldwell's varpi parameter, emphasizing the connection to observations. It is anticipated that this framework will be of use in constraining individual models, as well as for placing model-independent constraints on dark energy and modified gravity model building.
Towards a Theory of Nonassociative Gravity
Blumenhagen, Ralph
2016-01-01
Violating the strong constraint of double field theory, non-geometric fluxes were argued to give rise to noncommutative/nonassociative structures. We derive in a rather pedestrian physicist way a differential geometry on the simplest nonassociative (phase-)space arising for a constant non-geometric R-flux. This provides a complementary presentation to the quasi-Hopf representation categorial one delivered by Barnes, Schenkel, Szabo in arXiv:1409.6331+1507.02792. As there, the notions of tensors, covariant derivative, torsion and curvature find a star-generalization. We continue the construction with the introduction of a star-metric and its star-inverse where, due to the nonassociativity, we encounter major deviations from the familiar structure. Comments on the Levi-Civita connection, a star-Einstein-Hilbert action and the relation to string theory are included, as well.
Beyond Einstein Gravity A Survey of Gravitational Theories for Cosmology and Astrophysics
Faraoni, Valerio
2011-01-01
Beyond Einstein’s Gravity is a graduate level introduction to extended theories of gravity and cosmology, including variational principles, the weak-field limit, gravitational waves, mathematical tools, exact solutions, as well as cosmological and astrophysical applications. The book provides a critical overview of the research in this area and unifies the existing literature using a consistent notation. Although the results apply in principle to all alternative gravities, a special emphasis is on scalar-tensor and f(R) theories. They were studied by theoretical physicists from early on, and in the 1980s they appeared in attempts to renormalize General Relativity and in models of the early universe. Recently, these theories have seen a new lease of life, in both their metric and metric-affine versions, as models of the present acceleration of the universe without introducing the mysterious and exotic dark energy. The dark matter problem can also be addressed in extended gravity. These applications are contr...
On Wormhole Throats in $f(R)$ Gravity Theory
DeBenedictis, Andrew
2011-01-01
We study the existence and properties of wormhole throats in modified $f(R)$ gravity theory. Specifically, we concentrate on the cases where the lapse is not necessarily constant, and hence are not limited to the zero tidal force scenarios. In the class of theories generated by Lagrangians of the form $f(R)=\\sum \\alpha_{n}\\,R^{n}$ we find parameters which allow for the existence of energy condition respecting throats, which do not exist in Einstein gravity. We also consider the effect of the modified Lagrangian on the anisotropy of the models, and find that modified gravity can minimize the amount of anisotropy required to support the existence of a throat. In both these respects, the sector containing theories with positive $n$ is more promising than the negative $n$ sector in comparison to Einstein gravity alone, with large $n$ being most favorable.
Bluhm, Robert
2016-01-01
Gravitational effective field theories with nondynamical backgrounds explicitly break diffeomorphism and local Lorentz invariance. At the same time, to maintain observer independence the action describing these theories is required to be mathematically invariant under general coordinate transformations and changes of local Lorentz bases. These opposing effects of having broken spacetime symmetries but invariance under mathematical observer transformations can result in theoretical inconsistency unless certain conditions hold. The consistency constraints that must hold originate from Noether identities associated with the mathematical observer invariances in the action. These identities are examined in detail and are used to investigate gravity theories with nondynamical backgrounds, including when a St\\"uckelberg approach is used. Specific examples include gravity theories with fixed scalar or tensor backgrounds, Einstein-Maxwell theory with a fixed external current, and massive gravity.
Bluhm, Robert; Šehić, Amar
2016-11-01
Gravitational effective field theories with nondynamical backgrounds explicitly break diffeomorphism and local Lorentz invariance. At the same time, to maintain observer independence the action describing these theories is required to be mathematically invariant under general coordinate transformations and changes of local Lorentz bases. These opposing effects of having broken spacetime symmetries but invariance under mathematical observer transformations can result in theoretical inconsistency unless certain conditions hold. The consistency constraints that must hold originate from Noether identities associated with the mathematical observer invariances in the action. These identities are examined in detail and are used to investigate gravity theories with nondynamical backgrounds, including when a Stückelberg approach is used. Specific examples include gravity theories with fixed scalar or tensor backgrounds, Einstein-Maxwell theory with a fixed external current, and massive gravity.
Newtonian semiclassical gravity in the Ghirardi–Rimini–Weber theory with matter density ontology
Energy Technology Data Exchange (ETDEWEB)
Derakhshani, Maaneli, E-mail: maanelid@yahoo.com
2014-03-01
We propose a Newtonian semiclassical gravity theory based on the GRW collapse theory with matter density ontology (GRWm), which we term GRWmN. The theory is proposed because, as we show from previous arguments in the literature, the standard Newtonian semiclassical gravity theory based on the Schroedinger–Newton equations does not have a consistent Born rule probability interpretation for gravitationally self-interacting particles and implies gravitational cat states for macroscopic mass superpositions. By contrast, we show that GRWmN has a consistent statistical description of gravitationally self-interacting particles and adequately suppresses the cat states for macroscopic superpositions. Two possible routes to experimentally testing GRWmN are also considered. We conclude with a discussion of possible variants of GRWmN, what a general relativistic extension would involve, and various objections that might be raised against semiclassical gravity theories like GRWmN.
Acausality and Non-Unique Evolution in Generalized Teleparallel Gravity
Izumi, Keisuke; Ong, Yen Chin
2013-01-01
We show the existence of physical superluminal modes and acausality in the Brans-Dicke type extension of teleparallel gravity that includes F(T) gravity and teleparallel dark energy as special cases. We derive the characteristic hypersurface for the extra degrees of freedom in the theory, thereby showing that the time evolution is not unique and closed causal curves can appear. Furthermore, we present a concrete disastrous solution in Bianchi type-I spacetime, in which the anisotropy in expansion can be any function of time and thus anisotropy can emerge suddenly, a simple demonstration that the theory is physically problematic.
Power-counting renormalizability of generalized Horava gravity
Visser, Matt
2009-01-01
In an earlier article [arXiv:0902.0590 [hep-th], Phys. Rev D80 (2009) 025011], I discussed the potential benefits of allowing Lorentz symmetry breaking in quantum field theories. In particular I discussed the perturbative power-counting finiteness of the normal-ordered :P(phi)^{z>=d}_{d+1}: scalar quantum field theories, and sketched the implications for Horava's model of quantum gravity. In the current rather brief addendum, I will tidy up some dangling issues and fill out some of the technical details of the argument indicating the power-counting renormalizability of a z>=d variant of Horava gravity in (d+1) dimensions.
Dimensionally reduced gravity theories are asymptotically safe
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Niedermaier, Max E-mail: max@phys.univ-tours.fr
2003-11-24
4D Einstein gravity coupled to scalars and abelian gauge fields in its 2-Killing vector reduction is shown to be quasi-renormalizable to all loop orders at the expense of introducing infinitely many essential couplings. The latter can be combined into one or two functions of the 'area radius' associated with the two Killing vectors. The renormalization flow of these couplings is governed by beta functionals expressible in closed form in terms of the (one coupling) beta function of a symmetric space sigma-model. Generically the matter coupled systems are asymptotically safe, that is the flow possesses a non-trivial UV stable fixed point at which the trace anomaly vanishes. The main exception is a minimal coupling of 4D Einstein gravity to massless free scalars, in which case the scalars decouple from gravity at the fixed point.
Generalized geometries and kinematics for Quantum Gravity
Cantcheff, M B
2000-01-01
The main objetive /proposal of this work Our proposal here is to set up the conceptual framework for an eventual {Theory of Everything}. We formulate the arena -language- to build up {\\it any} QG. In particular, we show how the objects of fundamental theories, such as p-branes (strings, loops and others) could be posed in this language.
Generalized uncertainty principle and analogue of quantum gravity in optics
Braidotti, Maria Chiara; Musslimani, Ziad H.; Conti, Claudio
2017-01-01
The design of optical systems capable of processing and manipulating ultra-short pulses and ultra-focused beams is highly challenging with far reaching fundamental technological applications. One key obstacle routinely encountered while implementing sub-wavelength optical schemes is how to overcome the limitations set by standard Fourier optics. A strategy to overcome these difficulties is to utilize the concept of a generalized uncertainty principle (G-UP) which has been originally developed to study quantum gravity. In this paper we propose to use the concept of G-UP within the framework of optics to show that the generalized Schrödinger equation describing short pulses and ultra-focused beams predicts the existence of a minimal spatial or temporal scale which in turn implies the existence of maximally localized states. Using a Gaussian wavepacket with complex phase, we derive the corresponding generalized uncertainty relation and its maximally localized states. Furthermore, we numerically show that the presence of nonlinearity helps the system to reach its maximal localization. Our results may trigger further theoretical and experimental tests for practical applications and analogues of fundamental physical theories.
Claudia de Rham
2016-01-01
We review recent progress in massive gravity. We start by showing how different theories of massive gravity emerge from a higher-dimensional theory of general relativity, leading to the Dvali-Gabadadze-Porrati model (DGP), cascading gravity, and ghost-free massive gravity. We then explore their theoretical and phenomenological consistency, proving the absence of Boulware-Deser ghosts and reviewing the Vainshtein mechanism and the cosmological solutions in these models. Finally, we present alt...
de Rham, Claudia
2014-01-01
We review recent progress in massive gravity. We start by showing how different theories of massive gravity emerge from a higher-dimensional theory of general relativity, leading to the Dvali-Gabadadze-Porrati model (DGP), cascading gravity, and ghost-free massive gravity. We then explore their theoretical and phenomenological consistency, proving the absence of Boulware-Deser ghosts and reviewing the Vainshtein mechanism and the cosmological solutions in these models. Finally, we present alt...
2014-01-01
We review recent progress in massive gravity. We start by showing how different theories of massive gravity emerge from a higher-dimensional theory of general relativity, leading to the Dvali–Gabadadze–Porrati model (DGP), cascading gravity, and ghost-free massive gravity. We then explore their theoretical and phenomenological consistency, proving the absence of Boulware–Deser ghosts and reviewing the Vainshtein mechanism and the cosmological solutions in these models. Finally, we present alt...
Unified cosmology with scalar-tensor theory of gravity
Energy Technology Data Exchange (ETDEWEB)
Tajahmad, Behzad [Faculty of Physics, University of Tabriz, Tabriz (Iran, Islamic Republic of); Sanyal, Abhik Kumar [Jangipur College, Department of Physics, Murshidabad (India)
2017-04-15
Unlike the Noether symmetry, a metric independent general conserved current exists for non-minimally coupled scalar-tensor theory of gravity if the trace of the energy-momentum tensor vanishes. Thus, in the context of cosmology, a symmetry exists both in the early vacuum and radiation dominated era. For slow roll, symmetry is sacrificed, but at the end of early inflation, such a symmetry leads to a Friedmann-like radiation era. Late-time cosmic acceleration in the matter dominated era is realized in the absence of symmetry, in view of the same decayed and redshifted scalar field. Thus, unification of early inflation with late-time cosmic acceleration with a single scalar field may be realized. (orig.)
Generalized Second Law of Thermodynamic in Modified Teleparallel Theory
Zubair, M
2016-01-01
This study is conducted to examine the validity of generalized second law of thermodynamics (GSLT) in modified teleparallel gravity involving coupling between a scalar field with the torsion scalar and a boundary term. This theory is very useful since it can reproduce other well-known theories in suitable limits. The power law solution is employed to develop the constraints on coupling parameters for different theories of gravity in the background of thermodynamics properties for all potentials. We have also considered the logarithmic entropy corrected relation and discuss the GSLT both on apparent and event horizons. In case of entropy correction, we have constrained the coupling parameters for quartic and inverse potentials.
Slice Energy in Higher Order Gravity Theories and Conformal Transformations
Cotsakis, S
2004-01-01
We show that there is a generic transport of energy between the scalar field generated by the conformal transformation of higher order gravity theories and the matter component. We give precise relations of this exchange and show that, unless we are in a stationary spacetime, slice energy is not generically conserved. These results translate into statements about the relative behaviour of ordinary matter, dark matter and dark energy in the context of higher order gravity.
Generalized Heisenberg theory of turbulence
Uberoi, M. S.; Narain, J. P.
1974-01-01
Solutions of the generalized theory are obtained which are consistent with the previous work on energy transfer measurements. They also agree with the measurements of turbulent energy spectrum for wave numbers in the universal equilibrium range.
Cosmological evolution of generalized non-local gravity
Zhang, Xue; Li, Song; Liu, Yu-Chen; Chen, Bo-Hai; Chai, Yun-Tian; Shu, Shuang
2015-01-01
We construct a class of generalized non-local gravity (GNLG) model which is the modified theory of general relativity (GR) obtained by adding a term $m^{2n-2} R\\Box^{-n}R$ to the Einstein-Hilbert action. Concretely, we not only study the gravitational equation for the GNLG model by introducing auxiliary scalar fields, but also analyse the classical stability and examine the cosmological consequences of the model for different exponent $n$. We find that the half of the scalar fields are always ghost-like and the exponent $n$ must be taken even number for a stable GNLG model. Meanwhile, the model spontaneously generates three dominant phases of the evolution of the universe, and the equation of state parameters turn out to be phantom-like. Furthermore, we clarify in another way that exponent $n$ should be even numbers by discuss the spherically symmetric static solutions in Newtonian gauge. It is worth stressing that the results given by us can include ones in refs. [24, 29, 31] as the special case of $n=2$.
Gravitomagnetic time delay and the Lense-Thirring effects in f(R) gravity theories
Energy Technology Data Exchange (ETDEWEB)
Santos, Noelia S.; Santos, Janilo [Universidade Federal do Rio Grande do Norte (UFRN), RN (Brazil)
2011-07-01
Full text: Recently, in face of the impressive amount of astrophysical data pointing to a phase of accelerated expansion of the universe, modified gravity models had a revival, mainly in the cosmological context. Perhaps the much simply of these models, f(R) gravity examines the possibility of modifying Einstein's general relativity by adding terms proportional to powers of the Ricci scalar R to the Einstein-Hilbert Lagrangian. Nowadays there is increasing interest in applications of f(R) gravity to cosmology motivated by the fact that these theories can exhibit naturally an accelerating late expansion phase without introducing exotic form of matter like the so called dark energy. However, when modifying gravity, one must ensure that general relativity is recovered in the well tested short scales like the solar system. As is well known, general relativity predicts interesting effects associated with rotations of massive bodies, the so called gravitomagnetic effects. The Lense-Thirring precession and the gravitomagnetic time delay are the much studied such effects in the weak field and slow motion approximation of general relativity, valid throughout the solar system. Here we investigate and discuss the gravitomagnetic time delay and the Lense-Thirring effects in the context of the f(R) theories of gravity. We obtain the equation of motion of a particle inside the gravitomagnetic field of a slowly rotating distribution of matter, in the framework of a general f(R) theory, and compare it with that obtained from the weak field approximation of general relativity. Moreover, we calculate the gravitomagnetic time delay in light ray propagation near a rotating mass in the context of f(R) gravity and discuss the observational consequences associated with some classes of these theories. (author)
The role of nonmetricity in metric-affine theories of gravity
Vitagliano, Vincenzo
2013-01-01
The intriguing choice to treat alternative theories of gravity by means of the Palatini approach, namely elevating the affine connection to the role of independent variable, contains the seed of some interesting (usually under-explored) generalizations of General Relativity, the metric-affine theories of gravity. The peculiar aspect of these theories is to provide a natural way for matter fields to be coupled to the independent connection through the covariant derivative built from the connection itself. Adopting a procedure borrowed from the effective field theory prescriptions, we study the dynamics of metric-affine theories of increasing order, that in the complete version include invariants built from curvature, nonmetricity and torsion. We show that even including terms obtained from nonmetricity and torsion to the second order density Lagrangian, the connection lacks dynamics and acts as an auxiliary field that can be algebraically eliminated, resulting in some extra interactions between metric and matt...
Kopeikin, S M; Kopeikin, Sergei; Fomalont, Ed
2002-01-01
A relativistic sub-picosecond model of gravitational time delay in radio astronomical observations is worked out and a new experimental test of general relativity is discussed in which the effect of retardation of gravity associated with its finite speed can be observed. As a consequence, the speed of gravity can be measured by differential VLBI observations. Retardation in propagation of gravity is a central part of the Einstein theory of general relativity which has not been tested directly so far. The idea of the proposed gravitational experiment is based on the fact that gravity in general relativity propagates with finite speed so that the deflection of light caused by the body must be sensitive to the ratio of the body's velocity to the speed of gravity. The interferometric experiment can be performed, for example, during the very close angular passage of a quasar by Jupiter. Due to the finite speed of gravity and orbital motion of Jupiter, the variation in its gravitational field reaches observer on Ea...
The curious history of relativity how Einstein's theory of gravity was lost and found again
Eisenstaedt, Jean
2006-01-01
Black holes may obliterate most things that come near them, but they saved the theory of general relativity. Einstein's theory was quickly accepted as the true theory of gravity after its publication in 1915, but soon took a back seat in physics to quantum mechanics and languished for decades on the blackboards of mathematicians. Not until the existence of black holes by Stephen Hawking and Roger Penrose in the 1960s, after Einstein's death, was the theory revived. Almost one hundred years after general relativity replaced Newton's theory of gravitation, The Curious History of Relativity tells the story of both events surrounding general relativity and the techniques employed by Einstein and the relativists to construct, develop, and understand his almost impenetrable theory. Jean Eisenstaedt, one of the world's leading experts on the subject, also discusses the theory's place in the evolution of twentieth-century physics. He describes the main stages in the development of general relativity: its beginnings,...
Post-Newtonian parameter $\\gamma$ for multiscalar-tensor gravity with a general potential
Hohmann, Manuel; Kuusk, Piret; Randla, Erik; Vilson, Ott
2016-01-01
We compute the parametrized post-Newtonian parameter $\\gamma$ in the case of a static point source for multiscalar-tensor gravity with completely general nonderivative couplings and potential in the Jordan frame. Similarly to the single massive field case $\\gamma$ depends exponentially on the distance from the source and is determined by the length of a vector of non-minimal coupling in the space of scalar fields and its orientation relative to the mass eigenvectors. Using data from the Cassini tracking experiment, we estimate bounds on a general theory with two scalar fields. Our formalism can be utilized for a wide range of models, which we illustrate by applying it to nonminimally coupled Higgs SU(2) doublet, general hybrid metric-Palatini gravity, linear ($\\Box^{-1}$) and quadratic ($\\Box^{-2}$) nonlocal gravity.
Time machines and traversable wormholes in modified theories of gravity
Directory of Open Access Journals (Sweden)
Lobo Francisco S.N.
2013-09-01
Full Text Available We review recent work on wormhole geometries in the context of modified theories of gravity, in particular, in f(R gravity and with a nonminimal curvature-matter coupling, and in the recently proposed hybrid metric-Palatini theory. In principle, the normal matter threading the throat can be shown to satisfy the energy conditions and it is the higher order curvatures terms that sustain these wormhole geometries. We also briefly review the conversion of wormholes into time-machines, explore several of the time travel paradoxes and possible remedies to these intriguing side-effects in wormhole physics.
Gravity-induced birefringence within the framework of Poincare gauge theory
Preuss, O; Haugan, Mark P; Jordan, S; Preuss, Oliver; Solanki, Sami K.; Jordan, Stefan
2005-01-01
Gauge theories of gravity provide an elegant and promising extension of general relativity. In this paper we show that the Poincar\\'e gauge theory exhibits gravity-induced birefringence under the assumption of a specific gauge invariant nonminimal coupling between torsion and Maxwell's field. Furthermore we give for the first time an explicit expression for the induced phaseshift between two orthogonal polarization modes within the Poincar\\'e framework. Since such a phaseshift can lead to a depolarization of light emitted from an extended source this effect is, in principle, observable. We use white dwarf polarimetric data to constrain the essential coupling constant responsible for this effect.
Inflation in $f(R,\\phi)$-theories and mimetic gravity scenario
Myrzakulov, R; Vagnozzi, S
2015-01-01
We investigate inflation within $f(R,\\phi)$-theories, where a dynamical scalar field is coupled to gravity. A class of models which can support early-time acceleration with the emerging of an effective cosmological constant at high curvature is studied. The dynamics of the field allow for exit from inflation leading to the correct amount of inflation in agreement with cosmological data. Furthermore, the spectral index and tensor-to-scalar ratio of the models are carefully analyzed. A generalization of the theory to incorporate dark matter in the context of mimetic gravity, and further extensions of the latter, are also discussed.
Inflation in f(R,φ)-theories and mimetic gravity scenario
Energy Technology Data Exchange (ETDEWEB)
Myrzakulov, R.; Sebastiani, L. [Eurasian National University, Department of General and Theoretical Physics and Eurasian Center for Theoretical Physics, Astana (Kazakhstan); Vagnozzi, S. [University of Copenhagen, Niels Bohr International Academy and Discovery Center, Niels Bohr Institute, Copenhagen Oe (Denmark); Nordita, KTH Royal Institute of Technology and Stockholm University, Stockholm (Sweden); Stockholm University, AlbaNova, Department of Physics, The Oskar Klein Centre for Cosmoparticle Physics, Stockholm (Sweden); University of Melbourne, ARC Centre of Excellence for Particle Physics at the Terascale, School of Physics, Melbourne, VIC (Australia)
2015-09-15
We investigate inflation within f(R,φ)-theories, where a dynamical scalar field is coupled to gravity. A class of models which can support early-time acceleration with the emerging of an effective cosmological constant at high curvature is studied. The dynamics of the field allow for exit from inflation leading to the correct amount of inflation in agreement with cosmological data. Furthermore, the spectral index and tensor-to-scalar ratio of the models are carefully analyzed. A generalization of the theory to incorporate dark matter in the context of mimetic gravity, and further extensions of the latter, are also discussed. (orig.)
Asymptotic symmetry and conservation laws in 2d Poincaré gauge theory of gravity
Blagojevic, M; Vukasinac, T
1996-01-01
The structure of the asymptotic symmetry in the Poincar\\'e gauge theory of gravity in 2d is clarified by using the Hamiltonian formalism. The improved form of the generator of the asymptotic symmetry is found for very general asymptotic behaviour of phase space variables, and the related conserved quantities are explicitly constructed.
On the embedding of quantum field theory on curved spacetimes into loop quantum gravity
Energy Technology Data Exchange (ETDEWEB)
Stottmeister, Alexander
2015-07-15
The main theme of this thesis is an investigation into possible connections between loop quantum gravity and quantum field theory on curved spacetimes: On the one hand, we aim for the formulation of a general framework that allows for a derivation of quantum field theory on curved spacetimes in a semi-classical limit. On the other hand, we discuss representation-theoretical aspects of loop quantum gravity and quantum field theory on curved spacetimes as both of the latter presumably influence each other in the aforesaid semi-classical limit. Regarding the first point, we investigate the possible implementation of the Born-Oppenheimer approximation in the sense of space-adiabatic perturbation theory in models of loop quantum gravity-type. In the course of this, we argue for the need of a Weyl quantisation and an associated symbolic calculus for loop quantum gravity, which we then successfully define, at least to a certain extent. The compactness of the Lie groups, which models a la loop quantum gravity are based on, turns out to be a main obstacle to a fully satisfactory definition of a Weyl quantisation. Finally, we apply our findings to some toy models of linear scalar quantum fields on quantum cosmological spacetimes and discuss the implementation of space-adiabatic perturbation theory therein. In view of the second point, we start with a discussion of the microlocal spectrum condition for quantum fields on curved spacetimes and how it might be translated to a background-independent Hamiltonian quantum theory of gravity, like loop quantum gravity. The relevance of this lies in the fact that the microlocal spectrum condition selects a class of physically relevant states of the quantum matter fields and is, therefore, expected to play an important role in the aforesaid semi-classical limit of gravity-matter systems. Following this, we switch our perspective and analyse the representation theory of loop quantum gravity. We find some intriguing relations between the
Scalar theory of gravity as a pressure force
Arminjon, Mayeul
1997-01-01
The theory starts from a tentative interpretation of gravity as Archimedes' thrust exerted on matter at the scale of elementary particles by an imagined perfect fluid ("ether"): the gravity acceleration is expressed by a formula in which the "ether pressure" p_e plays the role of the Newtonian potential. The instantaneous propagation of Newtonian gravity is obtained with an incompressible ether, giving a field equation for p_e. For a compressible ether, this equation holds in the static case. The extension to non-static situations follows the lines of acoustics and leads to gravitational (pressure) waves. To account for metric effects, the modern version of the Lorentz-Poincare interpretation of special relativity is used. Einstein's equivalence principle (EP) is seen as a correspondence between the metric effects of gravity and those of uniform motion with respect to the ether: a gravitational contraction (dilation) of space (time) standards is assumed. This implies geodesic motion for test particles in a st...
f(R) gravity theory and CMBR constraints
Hwang, J
2001-01-01
We consider the large-scale cosmic structure generation by an inflation based on a pure f(R)-type gravity theory. Comparison with recent CMBR observations gives the following results: (1) The near Zel'dovich spectral conditions uniquely choose R^2-type gravity. (2) The R^2 gravity predicts specific nearly scale-invariant Zel'dovich spectra for both the scalar- and tensor-type perturbations. Thus, (3) the considered model survives current observational data. The COBE-DMR quadrupole data (4) give constraints on the coupling constant and the energy scale during inflation, and (5) require the gravitational wave contribution to be suppressed. (6) Therefore, future observations of (2) and (5) can provide strong tests of the inflation scenario based on R^2 gravity. Parallel analyses made in the conformally transformed Einstein frame give the observationally identical results.
Massive gravitational waves from f(R) theories of gravity: Potential detection with LISA
Energy Technology Data Exchange (ETDEWEB)
Capozziello, Salvatore [Dipartimento di Scienze Fisiche, Universita di Napoli ' Federico II' , INFN Sezione di Napoli, Complesso Universitario di Monte S. Angelo, Edificio G, via Cintia, I-80126 Napoli (Italy)], E-mail: capozzie@na.infn.it; Corda, Christian [Associazione Galileo Galilei, via Pier Cironi 16, 59100 Prato (Italy); Centro di Scienze Naturali, via di Galceti 74, 59100 Prato (Italy)], E-mail: christian.corda@ego-gw.it; De Laurentis, Maria Felicia [Relativity and Gravitation Group, Politecnico di Torino, Corso Duca degli Abruzzi 24, I-10129 Torino (Italy)], E-mail: mariafelicia.delaurentist@polito.it
2008-11-27
This Letter is a generalization of previous results on gravitational waves (GWs) from f(R) theories of gravity. In some previous papers, particular f(R) theories have been linearized for the first time in the literature. Now, the process is further generalized, showing that every f(R) theory can be linearized producting a third massive mode of gravitational radiation. In this framework, previous results are particular cases of the more general problem that is discussed in this Letter. The potential detectability of such massive GWs with LISA is also discussed with the auxilium of longitudinal response functions.
Massive gravitational waves from f(R) theories of gravity: Potential detection with LISA
Capozziello, Salvatore; De Laurentis, Maria Felicia
2008-01-01
This letter is a generalization of previous results on gravitational waves (GWs) from f(R) theories of gravity. In some previous papers, particular f(R) theories have been linearized for the first time in the literature. Now, the process is further generalized, showing that every f(R) theory can be linearized producting a third massive mode of gravitational radiation. In this framework, previous results are particular cases of the more general problem that is discussed in this letter. The potential detectability of such massive GWs with LISA is also discussed with the auxilium of longitudinal response functions.
Generalized Recursion Relations for Correlators in the Gauge-Gravity Correspondence
Raju, Suvrat
2011-03-01
We show that a generalization of the Britto-Cachazo-Feng-Witten recursion relations gives a new and efficient method of computing correlation functions of the stress tensor or conserved currents in conformal field theories with an (d+1)-dimensional anti-de Sitter space dual, for d≥4, in the limit where the bulk theory is approximated by tree-level Yang-Mills theory or gravity. In supersymmetric theories, additional correlators of operators that live in the same multiplet as a conserved current or stress tensor can be computed by these means.
How Do You Solve a Problem Like Modified Gravity? Challenges in Connecting Theory and Observations
Linder, Eric V
2016-01-01
Cosmic acceleration may be due to modifications of cosmic gravity. To test this we need robust connections between theory and observations. However, in a model independent approach like effective field theory or a broad class like Horndeski gravity, several free functions of time enter the theory. We demonstrate that no simple parametrizations of these functions are valid, with first approximations such as $\\alpha_i(t)\\propto\\Omega_{\\rm de}(t)$ drastically misestimating the observables. Quantifying the bias, we find that even a few percent inaccuracy on the property functions $\\alpha_i(t)$ give many expected-sigma bias on cosmic survey observables (often missing the signature of modified gravity). We also address the challenge of generally valid consistency relations and the role of tensor (gravitational wave) perturbations.
Large-Scale Structure in Brane-Induced Gravity I. Perturbation Theory
Scoccimarro, Roman
2009-01-01
We study the growth of subhorizon perturbations in brane-induced gravity using perturbation theory. We solve for the linear evolution of perturbations taking advantage of the symmetry under gauge transformations along the extra-dimension to decouple the bulk equations in the quasistatic approximation, which we argue may be a better approximation at large scales than thought before. We then study the nonlinearities in the bulk and brane equations, concentrating on the workings of the Vainshtein mechanism by which the theory becomes general relativity (GR) at small scales. We show that at the level of the power spectrum, to a good approximation, the effect of nonlinearities in the modified gravity sector may be absorbed into a renormalization of the gravitational constant. Since weak lensing is entirely unaffected by the extra nonlinear physics in these theories, the modified gravity can be described in this approximation by a single function, an effective gravitational constant that depends on space and time. ...
Modified teleparallel theories of gravity: Gauss-Bonnet and trace extensions
Energy Technology Data Exchange (ETDEWEB)
Bahamonde, Sebastian; Boehmer, Christian G. [University College London, Department of Mathematics, London (United Kingdom)
2016-10-15
We investigate modified theories of gravity in the context of teleparallel geometries with possible Gauss-Bonnet contributions. The possible coupling of gravity with the trace of the energy-momentum tensor is also taken into account. This is motivated by the various different theories formulated in the teleparallel approach and the metric approach without discussing the exact relationship between them. Our formulation clarifies the connections between different well-known theories. For instance, we are able to formulate the correct teleparallel equivalent of Gauss-Bonnet modified general relativity, amongst other results. Finally, we are able to identify modified gravity models which have not been studied in the past. These appear naturally within our setup and would make a interesting starting point for further studies. (orig.)
Modified teleparallel theories of gravity: Gauss-Bonnet and trace extensions.
Bahamonde, Sebastian; Böhmer, Christian G
2016-01-01
We investigate modified theories of gravity in the context of teleparallel geometries with possible Gauss-Bonnet contributions. The possible coupling of gravity with the trace of the energy-momentum tensor is also taken into account. This is motivated by the various different theories formulated in the teleparallel approach and the metric approach without discussing the exact relationship between them. Our formulation clarifies the connections between different well-known theories. For instance, we are able to formulate the correct teleparallel equivalent of Gauss-Bonnet modified general relativity, amongst other results. Finally, we are able to identify modified gravity models which have not been studied in the past. These appear naturally within our setup and would make a interesting starting point for further studies.
The Cosmology of Generalized Modified Gravity Models
Carroll, S M; Duvvuri, V; Easson, D A; Trodden, M; Turner, M S; Carroll, Sean M.; Felice, Antonio De; Duvvuri, Vikram; Easson, Damien A.; Trodden, Mark; Turner, Michael S.
2005-01-01
We consider general curvature-invariant modifications of the Einstein-Hilbert action that become important only in regions of extremely low space-time curvature. We investigate the far future evolution of the universe in such models, examining the possibilities for cosmic acceleration and other ultimate destinies. The models generically possess de Sitter space as an unstable solution and exhibit an interesting set of attractor solutions which, in some cases, provide alternatives to dark energy models.
Cosmology of generalized modified gravity models
Carroll, Sean M.; de Felice, Antonio; Duvvuri, Vikram; Easson, Damien A.; Trodden, Mark; Turner, Michael S.
2005-03-01
We consider general curvature-invariant modifications of the Einstein-Hilbert action that become important only in regions of extremely low space-time curvature. We investigate the far future evolution of the Universe in such models, examining the possibilities for cosmic acceleration and other ultimate destinies. The models generically possess de Sitter space as an unstable solution and exhibit an interesting set of attractor solutions which, in some cases, provide alternatives to dark energy models.
Generalized Curvature-Matter Couplings in Modified Gravity
Directory of Open Access Journals (Sweden)
Tiberiu Harko
2014-07-01
Full Text Available In this work, we review a plethora of modified theories of gravity with generalized curvature-matter couplings. The explicit nonminimal couplings, for instance, between an arbitrary function of the scalar curvature R and the Lagrangian density of matter, induces a non-vanishing covariant derivative of the energy-momentum tensor, implying non-geodesic motion and, consequently, leads to the appearance of an extra force. Applied to the cosmological context, these curvature-matter couplings lead to interesting phenomenology, where one can obtain a unified description of the cosmological epochs. We also consider the possibility that the behavior of the galactic flat rotation curves can be explained in the framework of the curvature-matter coupling models, where the extra terms in the gravitational field equations modify the equations of motion of test particles and induce a supplementary gravitational interaction. In addition to this, these models are extremely useful for describing dark energy-dark matter interactions and for explaining the late-time cosmic acceleration.
Theoretical and observational constraints of viable f(R) theories of gravity
de la Cruz-Dombriz, Alvaro; Kandhai, Sulona; Saez-Gomez, Diego
2015-01-01
Modified gravity has attracted much attention over the last few years and remains a potential candidate for dark energy. In particular, the so-called viable f(R) gravity theories, which are able to both recover General Relativity (GR) and produce late-time cosmic acceleration, have been widely studied in recent literature. Nevertheless, extended theories of gravity suffer from several shortcomings which compromise their ability to provide realistic alternatives to the standard cosmological Lambda CDM Concordance model. We address the existence of cosmological singularities and the conditions that guarantee late-time acceleration,assuming reasonable energy conditions for standard matter in the so-called Hu-Sawicki f(R) model, currently among the most widely studied modifications to General Relativity. Then using the Supernovae Ia Union 2.1 catalogue, we further constrain the free parameters of this model. The combined analysis of both theoretical and observational constraints sheds some light on the viable par...
Generalized $f(R,\\phi,X)$ gravity and the late-time cosmic acceleration
Beltran, Sebastian Bahamonde; Lobo, Francisco S N; Saez-Gomez, Diego
2015-01-01
High-precision observational data have confirmed with startling evidence that the Universe is currently undergoing a phase of accelerated expansion. This phase, one of the most important and challenging current problems in cosmology, represents a new imbalance in the governing gravitational equations. Historically, physics has addressed such imbalances by either identifying sources that were previously unaccounted for, or by altering the gravitational theory. Several candidates, responsible for this expansion, have been proposed in the literature, in particular, dark energy models and modified gravity models, amongst others. Outstanding questions are related to the nature of this so-called "dark energy" that is driving this acceleration, and whether it is due to the vacuum energy or a dynamical field. On the other hand, the late-time cosmic acceleration may be due to modifications of General Relativity. In this work we explore a generalised modified gravity theory, namely $f(R,\\phi,X)$ gravity, where $R$ is t...
Screening fifth forces in generalized Proca theories
De Felice, Antonio; Heisenberg, Lavinia; Kase, Ryotaro; Tsujikawa, Shinji; Zhang, Ying-li; Zhao, Gong-Bo
2016-05-01
For a massive vector field with derivative self-interactions, the breaking of the gauge invariance allows the propagation of a longitudinal mode in addition to the two transverse modes. We consider generalized Proca theories with second-order equations of motion in a curved space-time and study how the longitudinal scalar mode of the vector field gravitates on a spherically symmetric background. We show explicitly that cubic-order self-interactions lead to the suppression of the longitudinal mode through the Vainshtein mechanism. Provided that the dimensionless coupling of the interaction is not negligible, this screening mechanism is sufficiently efficient to give rise to tiny corrections to gravitational potentials consistent with solar-system tests of gravity. We also study the quartic interactions with the presence of nonminimal derivative coupling with the Ricci scalar and find the existence of solutions where the longitudinal mode completely vanishes. Finally, we discuss the case in which the effect of the quartic interactions dominates over the cubic one and show that local gravity constraints can be satisfied under a mild bound on the parameters of the theory.
Faller, Sven
2007-01-01
In the last years a lot of papers were published treating general relativity as an effective field theory. We are dealing with general relativity and the combination of general relativity and scalar QED as effective field theories. For effective field theories the quantization is well known therefore we are able to quantize general relativity and the combination of general relativity and scalar QED. The vertex rules can be extracted from the action and the non-analytical contributions to the 1-loop scattering matrix of scalars and charged scalars are calculated in the non-relativistic limit. The non-analytical parts of the scattering amplitudes yield the long range, low energy, leading quantum corrections. From the general relativity as an effective field theory the leading quantum corrections to the Newtonian gravity is constructed. General relativity combined with scalar QED yield the post-Newtonian and quantum corrections to the two-particle non-relativistic scattering matrix potential for charged scalar p...
Abelian Chern-Simons theory, Stokes' Theorem, and generalized connections
Sahlmannn, Hanno
2010-01-01
Generalized connections and their calculus have been developed in the context of quantum gravity. Here we apply them to abelian Chern-Simons theory. We derive the expectation values of holonomies in U(1) Chern-Simons theory using Stokes' Theorem, flux operators and generalized connections. A framing of the holonomy loops arises in our construction, and we show how, by choosing natural framings, the resulting expectation values nevertheless define a functional over gauge invariant cylindrical functions. The abelian theory considered in the present article is test case for our method. It can also be applied to the non-abelian theory. Results for that case will be reported elsewhere.
Directory of Open Access Journals (Sweden)
Suhendro I.
2008-01-01
Full Text Available In this work, we attempt at constructing a comprehensive four-dimensional unified field theory of gravity, electromagnetism, and the non-Abelian Yang-Mills gauge field in which the gravitational, electromagnetic, and material spin fields are unified as intrinsic geometric objects of the space-time manifold $S_4$ via the connection, with the generalized non-Abelian Yang-Mills gauge field appearing in particular as a sub-field of the geometrized electromagnetic interaction.
Extended dilaton gravity theories in 1 + 1 dimensions
Energy Technology Data Exchange (ETDEWEB)
Mello, R.O. de [Universidade Tecnologica Federal do Parana (UTFPR), Curitiba (Brazil)
2013-07-01
Full text: We show that an anomaly-free description of matter in (1+1) dimensions requires a deformation of the 2d relativity principle, which introduces a non-trivial center in the 2d Poincare algebra. Then we work out the reduced phase-space of the anomaly-free 2d relativistic particle, in order to show that it lives in a noncommutative 2d Minkowski space. Moreover, we build a Gaussian wave packet to show that a Planck length is well-defined in two dimensions. In order to provide a gravitational interpretation for this noncommutativity, we propose to extend the usual 2d generalized dilaton gravity models by a specific Maxwell component, which gauges the extra symmetry associated with the center of the 2d Poincare algebra. In addition, we show that this extension is a high energy correction to the unextended dilaton theories that can affect the topology of space-time. Further, we couple a test particle to the general extended dilaton models with the purpose of showing that they predict a noncommutativity in curved space-time, which is locally described by a Moyal star product in the low energy limit. We also conjecture a probable generalization of this result, which provides a strong evidence that the noncommutativity is described by a certain star product which is not of the Moyal type at high energies. Finally, we prove that the extended dilaton theories can be formulated as Poisson-Sigma models based on a nonlinear deformation of the extended Poincare algebra. (author)
Noncommutative Gravity and Quantum Field Theory on Noncommutative Curved Spacetimes
Schenkel, Alexander
2012-01-01
The focus of this PhD thesis is on applications, new developments and extensions of the noncommutative gravity theory proposed by Julius Wess and his group. In part one we propose an extension of the usual symmetry reduction procedure to noncommutative gravity. We classify in the case of abelian Drinfel'd twists all consistent deformations of spatially flat Friedmann-Robertson-Walker cosmologies and of the Schwarzschild black hole. The deformed symmetry structure allows us to obtain exact solutions of the noncommutative Einstein equations in many of our models. In part two we develop a new formalism for quantum field theory on noncommutative curved spacetimes by combining methods from the algebraic approach to quantum field theory with noncommutative differential geometry. We also study explicit examples of deformed wave operators and find that there can be noncommutative corrections even on the level of free field theories. The convergent deformation of simple toy models is investigated and it is found that ...
Nonhomogeneous Cooling, Entropic Gravity and MOND Theory
Neto, Jorge Ananias
2011-11-01
In this paper, by using the holographic principle, a modified equipartition theorem where we assume that below a critical temperature the energy is not equally divided on all bits, and the Unruh temperature, we derive MOND theory and a modified Friedmann equation compatible with MOND theory. Furthermore, we rederive a modified Newton's law of gravitation by employing an adequate redefinition of the numbers of bits.
Nonhomogeneous Cooling, Entropic Gravity and MOND Theory
Neto, Jorge Ananias
2010-01-01
In this paper, by using the holographic principle, a modified equipartition theorem where we assume that below a critical temperature the energy is not equally divided on all bits, and the Unruh temperature, we derive MOND theory and a modified Friedmann equation compatible with MOND theory. Furthermore, we rederive a modified Newton's law of gravitation by employing an adequate redefinition of the numbers of bits.
Johnson-McDaniel, Nathan; Ghosh, Abhirup; Ghosh, Archisman; Samajdar, Anuradha; Ajith, Parameswaran; Del Pozzo, Walter
2016-03-01
We describe a variety of self-consistent modifications of the effective-one-body framework that yield kludge modified gravity inspiral-merger-ringdown (IMR) waveforms. These waveforms do not correspond to any particular modified theory of gravity, but offer parametrized deviations from general relativity in various regimes. They can thus be used to test the performance of various gravitational wave tests of general relativity (GR). As an example, we introduce the IMR consistency test, which tests for consistency between the estimations of the final mass and spin from the inspiral and merger-ringdown portions of a binary black hole waveform. We show that for reasonable source parameters and SNRs in Advanced LIGO, this test is able to detect a deviation from GR with high confidence for certain modifications of the GR energy flux that are not constrained by observations of the double pulsar. We also consider the performance of a parameterized test of GR on these kludge modified gravity waveforms.
The Cauchy Problem of Scalar Tensor Theories of Gravity
Salgado, M
2006-01-01
The 3+1 formulation of scalar-tensor theories of gravity (STT) is obtained in the physical (Jordan) frame departing from the 4+0 covariant field equations. Contrary to the common believe (folklore), the new system of ADM-like equations shows that the Cauchy problem of STT is well formulated (in the sense that the whole system is of first order in the time-derivative). This is the first step towards a full first order (in time and space) formulation from which a subsequent hyperbolicity analysis (a well-posedness determination) can be performed. Several gauge (lapse and shift) conditions are considered and implemented for STT. In particular, a generalization of the harmonic gauge for STT allows to prove the well posedness of the STT using a second order analysis which is very similar to the one used in general relativity. Some spacetimes of astrophysical and cosmological interest are considered as specific applications. Several appendices complement the ideas of the main part of the paper.
Investigating generalized parton distribution in gravity dual
Energy Technology Data Exchange (ETDEWEB)
Nishio, Ryoichi, E-mail: ryoichi.nishio@ipmu.jp [Department of Physics, University of Tokyo, Tokyo 113-0033 (Japan); Institute for the Physics and Mathematics of the Universe, University of Tokyo, Chiba 277-8583 (Japan); Watari, Taizan [Institute for the Physics and Mathematics of the Universe, University of Tokyo, Chiba 277-8583 (Japan)
2012-02-01
Generalized parton distribution (GPD) contains rich information of partons in a hadron, including transverse profile, and is also non-perturbative information necessary in describing a variety of hard processes, such as meson leptoproduction and double deeply virtual Compton scattering (DDVCS). In order to unveil non-perturbative aspects of GPD, we study DDVCS at small x in gravitational dual description. Using the complex spin j-plane representation of DDVCS amplitude, we show that GPD is well-defined and can be extracted from the amplitude even in the strong coupling regime. It also turns out that the saddle point value in the j-plane representation plays an important role; there are two phases in the imaginary part of amplitude of DDVCS and GPD, depending on relative position of the saddle point and the leading pole in the j-plane, and crossover between them is induced by the change of the kinematical variables. The saddle point value also directly controls kinematical variable dependence of many observables in one of the two phases, and indeed the dependence is qualitatively in nice agreement with HERA measurements. This Letter also serves as a brief summary of a preprint (arXiv:1105.2999).
Physics on all scales. Scalar-tensor theories of quantum gravity in particle physics and cosmology
Energy Technology Data Exchange (ETDEWEB)
Henz, Tobias
2016-05-10
In this thesis, we investigate dilaton quantum gravity using a functional renormalization group approach. We derive and discuss flow equations both in the background field approximation and using a vertex expansion as well as solve the fixed point equations globally to show how realistic gravity, connecting ultraviolet and infrared physics, can be realized on a pure fixed point trajectory by virtue of spontaneous breaking of scale invariance. The emerging physical system features a dynamically generated moving Planck scale resembling the Newton coupling as well as slow roll inflation with an exponentially decreasing effective cosmological constant that vanishes completely in the infrared. The moving Planck scale might make quantum gravity experimentally accessible at a different energy scale than previously believed. We therefore not only provide further evidence for the existence of a consistent quantum theory of gravity based on general relativity, but also offer potential solutions towards the hierarchy and cosmological constant problems, thereby opening up exciting opportunities for further research.
Quantum Aspects of Massive Gravity II: Non-Pauli-Fierz Theory
Park, Minjoon
2010-01-01
We investigate the non-Pauli-Fierz (nPF) theory, a linearized massive gravity with a generic graviton mass term, which has been ignored due to a ghost in its spectrum and the resultant loss of unitarity. We first show that it is possible to use the Lee-Wick mechanism, a unitarization through the decay of a ghost, in order to handle the sixth mode ghost of nPF, and then check for the quantum consistency. Once proven to be consistent, nPF could become a viable candidate for a large distance modification of gravity, because it naturally solves the intrinsic problems that most dark energy/modified gravity models suffer from: It smoothly converges to general relativity at short distances, and the small graviton mass necessary to modify gravity at large scales is radiatively stable.
Conformal Gravity with the most general ELKO Matter
Fabbri, Luca
2011-01-01
Recently we have constructed the conformal gravity with metric and torsion, finding the gravitational field equations that give the conservation laws and trace condition; in the present paper we apply this theory to the case of ELKO matter field, proving that their spin and energy densities once the matter field equations are considered imply the validity of the conservation laws and trace condition mentioned above.
Generalized SU(2) Proca Theory
Allys, Erwan; Rodriguez, Yeinzon
2016-01-01
Following previous works on generalized Abelian Proca theory, also called vector galileon, we investigate the massive extension of a SU(2) gauge theory, i.e. the generalized SU(2) Proca model, which could be dubbed non-Abelian vector galileon. This particular symmetry group permits fruitful applications in cosmology such as inflation driven by gauge fields. Our approach consists in building in a exhaustive way all the Lagrangians containing up to six contracted Lorentz indices. For this purpose, and after identifying by group theoretical considerations all the independent Lagrangians which can be written at these orders, we consider the only linear combinations propagating three degrees of freedom and having healthy dynamics for their longitudinal mode, i.e. whose pure St\\"uckelberg contribution turns into the SU(2) multi-galileon dynamics. Finally, and after having considered the curved space-time expansion of these Lagrangians, we discuss the form of the theory at all subsequent orders.
Generalized Lorenz-Mie Theories
Gouesbet, Gérard
2011-01-01
The Lorenz-Mie theory, describing the interaction between a homogeneous sphere and an electromagnetic plane wave, is likely to be one of the most famous theories in light scattering. But, with the advent of lasers and their increasing development in various fields, it has become too old-fashioned to meet most of the modern requisites. The book deals with generalized Lorenz-Mie theories when the illuminating beam is an electromagnetic arbitrary shaped beam, relying on the method of separation of variables. A particular emphasis is stressed on the case of the homogeneous sphere but other regular particles are considered too. An extensive discussion of the methods available to the evaluation of beam shape coefficients describing the illuminating beam is provided, and several methods are discussed. Applications concern many fields such as optical particle sizing and, more generally, optical particle characterization, morphology-dependent resonances, or mechanical effects of light for optical trapping, optical twe...
Generalized SU(2) Proca theory
Allys, Erwan; Peter, Patrick; Rodríguez, Yeinzon
2016-10-01
Following previous works on generalized Abelian Proca theory, also called vector Galileon, we investigate the massive extension of an SU(2) gauge theory, i.e., the generalized SU(2) Proca model, which could be dubbed non-Abelian vector Galileon. This particular symmetry group permits fruitful applications in cosmology such as inflation driven by gauge fields. Our approach consists in building, in an exhaustive way, all the Lagrangians containing up to six contracted Lorentz indices. For this purpose, and after identifying by group theoretical considerations all the independent Lagrangians which can be written at these orders, we consider the only linear combinations propagating 3 degrees of freedom and having healthy dynamics for their longitudinal mode, i.e., whose pure Stückelberg contribution turns into the SU(2) multi-Galileon dynamics. Finally, and after having considered the curved space-time expansion of these Lagrangians, we discuss the form of the theory at all subsequent orders.
Generalized Vaidya Solutions and Misner-Sharp mass for $n$-dimensional massive gravity
Hu, Ya-Peng; Zhang, Hongsheng
2016-01-01
Dynamical solutions are always of interests in gravity theories. We derive a series of generalized Vaidya solutions in the $n$-dimensional de Rham-Gabadadze-Tolley (dRGT) massive gravity with a singular reference metric. Similar to the case of the Einstein gravity, the generalized Vaidya solution can describe shining/absorbing stars. Moreover, we also find a more general Vaidya-like solution by introducing a more generic matter field than the pure radiation in the original Vaidya solution. As a result, the above generalized Vaidya solution is naturally included in this Vaidya-like solution as a special case. We investigate the thermodynamics for this Vaidya-like spacetime by using the unified first law, and present the generalized Misner-Sharp mass. Our results show that the generalized Minser-Sharp mass does exist in this spacetime. In addition, the usual Clausius relation $\\delta Q= TdS$ holds on the apparent horizon, which implicates that the massive gravity is in a thermodynamic equilibrium state. We find...
Gravity theory in SAP-geometry
Youssef, Nabil L; Taha, Ebtsam H
2014-01-01
The aim of the present paper is to construct a field theory in the context of absolute parallelism (Teleparallel) geometry under the assumption that the canonical connection is semi-symmetric. The field equations are formulated using a suitable Lagrangian first proposed by Mikhail and Wanas. The mathematical and physical consequences arising from the obtained field equations are investigated.
Motion in gauge theories of gravity
Tresguerres, Romualdo
2012-01-01
A description of motion is proposed, adapted to the composite bundle interpretation of Poincar\\'e Gauge Theory. Reference frames, relative positions and time evolution are characterized in gauge-theoretical terms. The approach is illustrated by an appropriate formulation of the familiar example of orbital motion induced by Schwarzschild spacetime.
General virial theorem for modified-gravity MOND
Milgrom, Mordehai
2014-01-01
An important and useful relation is known to hold in two specific MOND theories. It pertains to low-acceleration, isolated systems of pointlike masses, m_p, at positions r_p, subject to gravitational forces F_p. It reads sum_p r_p.F_p=-(2/3)(Ga0)^{1/2}[(\\sum_p m_p)^{3/2}-\\sum_p m_p^{3/2}]; a0 is the MOND acceleration constant. Here I show that this relation holds in the nonrelativistic limit of any modified-gravity MOND theory. It follows from only the basic tenets of MOND (as applied to such theories): departure from standard dynamics at accelerations below a0, and space-time scale invariance in the nonrelativistic, low-acceleration limit. This implies space-dilatation invariance of the static, gravitational-field equations, which, in turn, leads to the above point-mass virial relation. Thus, the various MOND predictions and tests based on this relation hold in any modified-gravity MOND theory. Since we do not know that any of the existing MOND theories point in the right direction, it is important to identi...
Einstein gravity 3-point functions from conformal field theory
Afkhami-Jeddi, Nima; Kundu, Sandipan; Tajdini, Amirhossein
2016-01-01
We study stress tensor correlation functions in four-dimensional conformal field theories with large $N$ and a sparse spectrum. Theories in this class are expected to have local holographic duals, so effective field theory in anti-de Sitter suggests that the stress tensor sector should exhibit universal, gravity-like behavior. At the linearized level, the hallmark of locality in the emergent geometry is that stress tensor three-point functions $\\langle TTT\\rangle$, normally specified by three constants, should approach a universal structure controlled by a single parameter as the gap to higher spin operators is increased. We demonstrate this phenomenon by a direct CFT calculation. Stress tensor exchange, by itself, violates causality and unitarity unless the three-point functions are carefully tuned, and the unique consistent choice exactly matches the prediction of Einstein gravity. Under some assumptions about the other potential contributions, we conclude that this structure is universal, and in particular...
Gravitational Collapse In Vaidya Space-time For Galileon Gravity Theory
Rudra, Prabir
2014-01-01
The motive of this work is to study gravitational collapse in Vaidya space-time embedded in Galileon gravity theory. Galileon gravity is in fact an infrared modification of Einstein gravity, which was proposed as a generalization of the 4D effective theory in DGP brane model. Vaidya's metric is used all over to follow the nature of future outgoing radial null geodesics. Detecting whether the central singularity is naked or wrapped by an event horizon, by the existence of future directed radial null geodesic emitted in past from the singularity is the basic objective. To point out the existence of positive trajectory tangent solution, both particular parametric cases (through tabular forms) and wide range contouring process have been applied. Precisely, the EoS in perfect fluid satisfies a wide range of phenomena: from dust to exotic fluid like dark energy. We have used the EoS parameter $k$ to determine the end collapse state in different cosmological era.
Screening fifth forces in generalized Proca theories
De Felice, Antonio; Kase, Ryotaro; Tsujikawa, Shinji; Zhang, Ying-li; Zhao, Gong-Bo
2016-01-01
For a massive vector field with derivative self-interactions, the breaking of the gauge invariance allows the propagation of a longitudinal mode in addition to the two transverse modes. We consider generalized Proca theories with second-order equations of motion in a curved space-time and study how the longitudinal scalar mode of the vector field gravitates on a spherically symmetric background. We show explicitly that cubic-order self-interactions lead to the suppression of the longitudinal mode through the Vainshtein mechanism. Provided that the dimensionless coupling of the interaction is not negligible, this screening mechanism is sufficiently efficient to give rise to tiny corrections to gravitational potentials consistent with solar-system tests of gravity. We also study the quartic interactions with the presence of non-minimal derivative coupling with the Ricci scalar and find the existence of solutions where the longitudinal mode completely vanishes. Finally, we discuss the case in which the effect of...
Modified equations in the theory of induced gravity. Solution to the cosmological constant problem
Zaripov, Farkhat
2013-01-01
This research is an extension of the author's article \\cite{zar}, in which conformally invariant generalization of string theory was suggested to higher-dimensional objects. Special cases of the proposed theory are Einstein's theory of gravity and string theory. This work is devoted to the formation of self-consistent equations of the theory of induced gravity \\cite{zar}, \\cite{zari} in the presence of matter in the form of a perfect fluid that interacts with scalar fields. The study is done to solve these equations for the case of the cosmological model. In this model time-evolving gravitational and cosmological "constants" take place which are determined by the square of scalar fields. The values of which can be matched with the observational data. The equations that describe the theory have solutions that can both match with the solutions of the standard theory of gravity as well as it can differ from it. This is due to the fact that the fundamental "constants" of the theory, such as gravitational and cosm...
Modular Theory, Non-Commutative Geometry and Quantum Gravity
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Wicharn Lewkeeratiyutkul
2010-08-01
Full Text Available This paper contains the first written exposition of some ideas (announced in a previous survey on an approach to quantum gravity based on Tomita-Takesaki modular theory and A. Connes non-commutative geometry aiming at the reconstruction of spectral geometries from an operational formalism of states and categories of observables in a covariant theory. Care has been taken to provide a coverage of the relevant background on modular theory, its applications in non-commutative geometry and physics and to the detailed discussion of the main foundational issues raised by the proposal.
Compact Stars in Eddington-inspired Born-Infeld Gravity and General Relativity
Sham, Yu Hin
In this thesis we apply the Eddington inspired Born-Infeld (EiBI) gravity to study the structure and the properties of compact stars. The hydrostatic equilibrium structure of compact stars characterized by different equations of state (EOSs) is considered and it is found that EiBI gravity can lead to different new features that are not found in standard general relativity (GR). A unified framework to study radial perturbations and the stability of compact stars in this theory is also developed. As in the GR case, the frequency- square of the fundamental oscillation mode vanishes for the maximum mass stellar configuration. Also, the oscillation modes depend on the parameter kappa introduced in EiBI gravity and the dependence is stronger for higher-order modes. We also discover that EiBI gravity imposes certain constraints on the EOSs that allow physical stable equilibrium states of compact stars to exist. However, such constraints are unphysical as the validity of an EOS should be independent of the theory of gravity, hinting that EiBI gravity needs to be modified. On the other hand, we demonstrate that two universal relations of compact stars, namely the I-Love-Q relation, which relates the moment of intertia, the tidal Love number and the quadrupole moment of compact stars, and the f-I relation, which links the f-mode oscillation frequency and the moment of inertia of compact stars together, still hold in EiBI gravity within the observational bounds of kappa. The origin of the two universal relations is then studied and it is found that a stiff EOS at the core of the compact star guarantees the universality. The two universal relations are further extended and universal relations relating the multipolar f-mode oscillation frequency and the corresponding multipolar tidal Love number, which can be derived analytically in the Newtonian limit for stars with sufficiently stiff EOSs, are found.
The Weak Gravity Conjecture and Effective Field Theory
Saraswat, Prashant
2016-01-01
The Weak Gravity Conjecture (WGC) is a proposed constraint on theories with gauge fields and gravity, requiring the existence of light charged particles and/or imposing an upper bound on the field theory cutoff $\\Lambda$. If taken as a consistency requirement for effective field theories (EFTs), it rules out possibilities for model-building including some models of inflation. I demonstrate simple models which satisfy all forms of the WGC, but which through Higgsing of the original gauge fields produce low-energy EFTs with gauge forces that badly violate the WGC. These models illustrate specific loopholes in arguments that motivate the WGC from a bottom-up perspective; for example the arguments based on magnetic monopoles are evaded when the magnetic confinement that occurs in a Higgs phase is accounted for. This indicates that the WGC should not be taken as a veto on EFTs, even if it turns out to be a robust property of UV quantum gravity theories. However, if the latter is true then parametric violation of t...
Solitons in generalized Galileon theories
Carrillo González, Mariana; Masoumi, Ali; Solomon, Adam R.; Trodden, Mark
2016-12-01
We consider the existence and stability of solitons in generalized Galileons, scalar-field theories with higher-derivative interactions but second-order equations of motion. It has previously been proven that no stable, static solitons exist in a single Galileon theory using an argument invoking the existence of zero modes for the perturbations. Here we analyze the applicability of this argument to generalized Galileons and discuss how this may be avoided by having potential terms in the energy functional for the perturbations or by including time dependence. Given the presence of potential terms in the Lagrangian for the perturbations, we find that stable, static solitons are not ruled out in conformal and (anti-)de Sitter Galileons. For the case of Dirac-Born-Infeld and conformal Galileons, we find that solitonic solutions moving at the speed of light exist, the former being stable and the latter unstable if the background soliton satisfies a certain condition.
Solitons in generalized galileon theories
Carrillo-Gonzalez, Mariana; Solomon, Adam R; Trodden, Mark
2016-01-01
We consider the existence and stability of solitons in generalized galileons, scalar field theories with higher-derivative interactions but second-order equations of motion. It has previously been proven that no stable, static solitons exist in a single galileon theory using an argument invoking the existence of zero modes for the perturbations. Here we analyze the applicability of this argument to generalized galileons and discuss how this may be avoided by having potential terms in the energy functional for the perturbations, or by including time dependence. Given the presence of potential terms in the Lagrangian for the perturbations, we find that stable, static solitons are not ruled out in conformal and (A)dS galileons. For the case of DBI and conformal galileons, we find that solitonic solutions moving at the speed of light exist, the former being stable and the latter unstable if the background soliton satisfies a certain condition.
Static and dynamic analysis of a massless scalar field coupled with a class of gravity theories
Kiem, Y H; Kiem, Youngjai; Park, Dahl
1995-01-01
General static solutions for a massless scalar field coupled to a class of effectively 2-d gravity theories continuously connecting spherically symmetric d-dimensional Einstein gravity (d >3) and the CGHS model are analytically obtained. They include black holes and point scalar charge solutions with naked singularities, and are used to give an analytic proof of no-hair theorem. Exact scattering solutions in s-wave 4-d Einstein gravity are constructed as a generalization of corresponding static solutions. They show the existence of black hole formation threshold for square pulse type incoming stress-energy flux, above which trapped surfaces are dynamically formed. The relationship between this behavior and the numerically studied phase transition in this system \\cite{choptuik} is discussed.
Dynamics of Generalized Tachyon Field in Teleparallel Gravity
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Behnaz Fazlpour
2015-01-01
Full Text Available We study dynamics of generalized tachyon scalar field in the framework of teleparallel gravity. This model is an extension of tachyonic teleparallel dark energy model which has been proposed by Banijamali and Fazlpour (2012. In contrast with tachyonic teleparallel dark energy model that has no scaling attractors, here we find some scaling attractors which means that the cosmological coincidence problem can be alleviated. Scaling attractors are presented for both interacting and noninteracting dark energy and dark matter cases.
Bathymetry Prediction Based on the Admittance Theory of Gravity Anomalies
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OUYANG Mingda
2015-10-01
Full Text Available Based on the admittance theory of gravity anomalies, the method of bathymetry prediction was studied in detail in this paper. In frequency domains, the correlation between gravity anomalies and bathymetry was analyzed, which suggests that the wavelength band correlated strongly was in a range of 20—300 km, this band was appropriated to inverse bathymetry by gravity anomalies. Took the Emperor Chain as an example, the uncompensated admittance model and flexural isostatic admittance model were used for researching, respectively, the included parameter of crust thickness and effective elastic thickness were calculated by the isostatic response function. As the down continuation factor was unstable, a high-cut filter was proposed in the inversion procedure to ensure convergence of series. The results showed that, the admittance theory of gravity anomalies can be used effectively in the bathymetry prediction, the predicted result was real and reliable, the relative precision was approximately 6%, which was equal to ETOPO1 model, and the detailed feature of sea floor which was not showed in ETOPO1 model can also be depicted; the precisions were not so well in areas of ocean mountains intensively distributed because of the complexion of the sea floor.
A Theory of Gravity Like Electrodynamics
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Rabounski D.
2005-07-01
Full Text Available This study looks at the field of inhomogeneities of time coordinates. Equations of motion, expressed through the field tensor, show that particles move along time lines because of rotation of the space itself. Maxwell-like equations of the field display its sources, which are derived from gravitation, rotations, and inhomogeneity of the space. The energy-momentum tensor of the field sets up an inhomogeneous viscous media, which is in the state of an ultrarelativistic gas. Waves of the field are transverse, and the wave pressure is derived from mainly sub-atomic processes - excitation/relaxation of atoms produces the positive/negative wave pressures, which leads to a test of the whole theory.
Planar Zeros in Gauge Theories and Gravity
Jimenez, Diego Medrano; Vazquez-Mozo, Miguel A
2016-01-01
Planar zeros are studied in the context of the five-point scattering amplitude for gauge bosons and gravitons. In the case of gauge theories, it is found that planar zeros are determined by an algebraic curve in the projective plane spanned by the three stereographic coordinates labelling the direction of the outgoing momenta. This curve depends on the values of six independent color structures. Considering the gauge group SU(N) with N=2,3,5 and fixed color indices, the class of curves obtained gets broader by increasing the rank of the group. For the five-graviton scattering, on the other hand, we show that the amplitude vanishes whenever the process is planar, without imposing further kinematic conditions. A rationale for this result is provided using color-kinematics duality.
Group field theory as the second quantization of loop quantum gravity
Oriti, Daniele
2016-04-01
We construct a second quantized reformulation of canonical loop quantum gravity (LQG) at both kinematical and dynamical level, in terms of a Fock space of spin networks, and show in full generality that it leads directly to the group field theory (GFT) formalism. In particular, we show the correspondence between canonical LQG dynamics and GFT dynamics leading to a specific GFT model from any definition of quantum canonical dynamics of spin networks. We exemplify the correspondence of dynamics in the specific example of 3d quantum gravity. The correspondence between canonical LQG and covariant spin foam models is obtained via the GFT definition of the latter.
Group field theory as the 2nd quantization of Loop Quantum Gravity
Oriti, Daniele
2013-01-01
We construct a 2nd quantized reformulation of canonical Loop Quantum Gravity at both kinematical and dynamical level, in terms of a Fock space of spin networks, and show in full generality that it leads directly to the Group Field Theory formalism. In particular, we show the correspondence between canonical LQG dynamics and GFT dynamics leading to a specific GFT model from any definition of quantum canonical dynamics of spin networks. We exemplify the correspondence of dynamics in the specific example of 3d quantum gravity. The correspondence between canonical LQG and covariant spin foam models is obtained via the GFT definition of the latter.
Hamiltonian approach to GR - Part 2: covariant theory of quantum gravity
Cremaschini, Claudio
2016-01-01
A non-perturbative quantum field theory of General Relativity is presented which leads to a new realization of the theory of Covariant Quantum-Gravity (CQG-theory). The treatment is founded on the recently-identified Hamiltonian structure associated with the classical space-time, i.e., the corresponding manifestly-covariant Hamilton equations and the related Hamilton-Jacobi theory. As shown here the connection with CQG-theory is achieved via the classical GR Hamilton-Jacobi equation, leading to the realization of the CQG-wave equation in 4-scalar form for the corresponding CQG-state and wave-function. The new quantum wave equation exhibits well-known formal properties characteristic of quantum mechanics, including the validity of quantum hydrodynamic equations and suitably-generalized Heisenberg inequalities. In addition, it recovers the classical GR equations in the semiclassical limit, while admitting the possibility of developing further perturbative approximation schemes. Applications of the theory are po...
Action and entanglement in gravity and field theory.
Neiman, Yasha
2013-12-27
In nongravitational quantum field theory, the entanglement entropy across a surface depends on the short-distance regularization. Quantum gravity should not require such regularization, and it has been conjectured that the entanglement entropy there is always given by the black hole entropy formula evaluated on the entangling surface. We show that these statements have precise classical counterparts at the level of the action. Specifically, we point out that the action can have a nonadditive imaginary part. In gravity, the latter is fixed by the black hole entropy formula, while in nongravitating theories it is arbitrary. From these classical facts, the entanglement entropy conjecture follows by heuristically applying the relation between actions and wave functions.
On powercounting in perturbative quantum gravity theories through color-kinematic duality
Boels, Rutger H.; Isermann, Reinke Sven
2013-06-01
The standard argument why gravity is not renormalisable relies on direct powercounting of Feynman graphs to estimate the degree of UV divergence. In several (highly) supersymmetric examples the actual divergences have been shown to be considerably better. In these examples the improvement follows from a conjectured duality between color and kinematics. In this paper we initiate the systematic study of quite general powercounting under the assumption that color-kinematic duality exists. The main technical tool is a reformulation of the duality in terms of linear maps, modulo subtleties at loop level mostly inherent to the duality. This tool may have wider applications in both gauge and gravity theories, up to resolution of the subtleties. Here it is first applied to the large Britto-Cachazo-Feng-Witten (BCFW) shift behavior of gravity integrands constructed through the duality. Assuming color-kinematic duality and reasonable technical requirements hold these shifts are shown to be independent of loop order. This is a new quantitative measure for massive cancellations with respect to the Feynman graph expression. More speculatively, the same approach is then applied to provide estimates of the overall degree of UV divergence in quite general gravity theories, assuming the duality exists. The manifest cancellations obtained in these estimates depends on the exact implementation of the duality at loop level, especially on graph topology. The developed arguments apply to all multiplicity. Finally, some evidence for the duality to all loop orders is provided from an analysis of BCFW shifts of gauge theory integrands through Feynman graphs.
A Curious Relation Between Gravity and Yang-Mills Theories
Baulieu, L
2000-01-01
We find that Euclidian or Minkowski gravity in d dimensions can be formally expressed as the restriction to a slice of a supersymmetric Yang-Mills theory in d+1 dimensions with SO(d+1), SO(d,1) or SO(d-1,2) internal symmetry. We suggest that renormalization effects in the bulk imply a contraction of the latter symmetry into the Poincare group ISO(d) or ISO(d-1,1).
On the stability conditions for theories of modified gravity in the presence of matter fields
De Felice, Antonio; Frusciante, Noemi; Papadomanolakis, Georgios
2017-03-01
We present a thorough stability analysis of modified gravity theories in the presence of matter fields. We use the Effective Field Theory framework for Dark Energy and Modified Gravity to retain a general approach for the gravity sector and a Sorkin-Schutz action for the matter one. Then, we work out the proper viability conditions to guarantee in the scalar sector the absence of ghosts, gradient and tachyonic instabilities. The absence of ghosts can be achieved by demanding a positive kinetic matrix, while the lack of a gradient instability is ensured by imposing a positive speed of propagation for all the scalar modes. In case of tachyonic instability, the mass eigenvalues have been studied and we work out the appropriate expressions. For the latter, an instability occurs only when the negative mass eigenvalue is much larger, in absolute value, than the Hubble parameter. We discuss the results for the minimally coupled quintessence model showing for a particular set of parameters two typical behaviours which in turn lead to a stable and an unstable configuration. Moreover, we find that the speeds of propagation of the scalar modes strongly depend on matter densities, for the beyond Horndeski theories. Our findings can be directly employed when testing modified gravity theories as they allow to identify the correct viability space.
Horizon Fluffs: In the Context of Generalized Minimal Massive Gravity
Setare, M R
2016-01-01
We consider a metric which describes Ba$\\tilde{\\text{n}}$ados geometries and show that the considered metric is a solution of generalized minimal massive gravity (GMMG) model. We consider the Killing vector field which preserves the form of considered metric. Using the off-shell quasi-local approach we obtain the asymptotic conserved charges of given solution. Similar to the Einstein gravity in the presence of negative cosmological constant, for the GMMG model also, we show that the algebra among the asymptotic conserved charges is isomorphic to two copies of the Virasoro algebra. Eventually, we find relation between the algebra of the near horizon and the asymptotic conserved charges. This relation show that the main part of the horizon fluffs proposal of Refs.\\cite{140,14} appear for generic black holes in the class of Ba$\\tilde{\\text{n}}$ados geometries in the context of GMMG model.
Solar system constraints on some Horndeski gravity theories
Bhattacharya, Sourav
2016-01-01
We discuss two spherically symmetric solutions admitted by the Horndeski (or scalar tensor) theory in the context of solar system physics. One of these solutions is derived for Einstein-Gauss-Bonnet gravity, while the other originates from the coupling of the Gauss-Bonnet invariant with a scalar field. Specifically, we discuss the perihelion precession of the Mercury and the bending angle of light for these two different spherically symmetric spacetimes derived in arXiv hep-th/0611188 and 1408.1698 respectively. Numerical bounds on relevant parameters of these theories from such computations are also presented.
A Contextualised General Systems Theory
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Kirsty Kitto
2014-10-01
Full Text Available A system is something that can be separated from its surrounds, but this definition leaves much scope for refinement. Starting with the notion of measurement, we explore increasingly contextual system behaviour and identify three major forms of contextuality that might be exhibited by a system: (1 between components; (2 between system and experimental method; and (3 between a system and its environment. Quantum theory is shown to provide a highly useful formalism from which all three forms of contextuality can be analysed, offering numerous tests for contextual behaviour, as well as modelling possibilities for systems that do indeed display it. I conclude with the introduction of a contextualised general systems theory based on an extension of this formalism
Modified gravity and Space-Time-Matter theory
Darabi, F
2009-01-01
The correspondence between $f(R)$ theories of gravity and model theories explaining induced dark energy in a 5D Ricci-flat universe, known as the Space-Time-Matter theory (STM), is studied. It is shown that such correspondence may be used to interpret the four dimensional expressions, induced from geometry in 5D STM theories, in terms of the extra terms appearing in $f(R)$ theories of gravity. The method is demonstrated by providing an explicit example in which a given $f(R)$ is used to predict the properties of the corresponding 5D Ricci-flat universe. The accelerated expansion and the induced dark energy in a 5D Ricci-flat universe characterized by a big bounce is studied and it is shown that an arbitrary function $\\mu(t)$ in the 5D solutions can be rewritten, in terms of the redshift $z$, as a new arbitrary function $F(z)$ which corresponds to the 4D curvature quintessence models.
Gestalt Therapy and General System Theory.
Whitner, Phillip A.
While General Systems Theory (GST) concepts appear to be applicable in explaining some of the phenomena that occur in a Gestalt Therapy group, research is needed to support this assumption. General Systems Theory may not be a group theory per se. Instead, GST may be a theory about groups. A meta-theory exists where its value and usefulness is…
Petrov, Alexander N
2013-01-01
A construction of conservation laws and conserved quantities for perturbations in arbitrary metric theories of gravity is developed. In an arbitrary field theory, with the use of incorporating an auxiliary metric into the initial Lagrangian covariantized Noether identities are carried out. Identically conserved currents with corresponding superpotentials are united into a family. Such a generalized formalism of the covariantized identities gives a natural basis for constructing conserved quantities for perturbations. A new family of conserved currents and correspondent superpotentials for perturbations on arbitrary curved backgrounds in metric theories is suggested. The conserved quantities are both of pure canonical Noether and of Belinfante corrected types. To test the results each of the superpotentials of the family is applied to calculate the mass of the Schwarzschild-anti-de Sitter black hole in the Einstein-Gauss-Bonnet gravity. Using all the superpotentials of the family gives the standard accepted ma...
Janiszewski, Stefan; Karch, Andreas
2013-02-22
We argue that generic nonrelativistic quantum field theories with a holographic description are dual to Hořava gravity. We construct explicit examples of this duality embedded in string theory by starting with relativistic dual pairs and taking a nonrelativistic scaling limit.
General Theory of Algebraic Equations
Bezout, Etienne
2008-01-01
This book provides the first English translation of Bezout's masterpiece, the General Theory of Algebraic Equations. It follows, by almost two hundred years, the English translation of his famous mathematics textbooks. Here, Bézout presents his approach to solving systems of polynomial equations in several variables and in great detail. He introduces the revolutionary notion of the "polynomial multiplier," which greatly simplifies the problem of variable elimination by reducing it to a system of linear equations. The major result presented in this work, now known as "Bézout's theorem," is stat
Analytical general solutions for static wormholes in f(R,T) gravity
Moraes, P. H. R. S.; Correa, R. A. C.; Lobato, R. V.
2017-07-01
Originally proposed as a tool for teaching the general theory of relativity, wormholes are today approached in many different ways and are seeing as an efficient alternative for interstellar and time travel. Attempts to achieve observational signatures of wormholes have been growing as the subject has become more and more popular. In this article we investigate some f(R,T) theoretical predictions for static wormholes, i.e., wormholes whose throat radius can be considered a constant. Since the T-dependence in f(R,T) gravity is due to the consideration of quantum effects, a further investigation of wormholes in such a theory is well motivated. We obtain the energy conditions of static wormholes in f(R,T) gravity and apply an analytical approach to find their physical and geometrical solutions. We highlight that our results are in agreement with previous solutions and assumptions presented in the literature.
Generalized Lorenz-Mie theories
Gouesbet, Gérard
2017-01-01
This book explores generalized Lorenz–Mie theories when the illuminating beam is an electromagnetic arbitrary shaped beam relying on the method of separation of variables. The new edition includes an additional chapter covering the latest advances in both research and applications, which are highly relevant for readers. Although it particularly focuses on the homogeneous sphere, the book also considers other regular particles. It discusses in detail the methods available for evaluating beam shape coefficients describing the illuminating beam. In addition it features applications used in many fields such as optical particle sizing and, more generally, optical particle characterization, morphology-dependent resonances and the mechanical effects of light for optical trapping, optical tweezers and optical stretchers. Furthermore, it provides various computer programs relevant to the content.
Holographic Renormalization of general dilaton-axion gravity
Papadimitriou, Ioannis
2011-01-01
We consider a very general dilaton-axion system coupled to Einstein-Hilbert gravity in arbitrary dimension and we carry out holographic renormalization for any dimension up to and including five dimensions. This is achieved by developing a new systematic algorithm for iteratively solving the radial Hamilton-Jacobi equation in a derivative expansion. The boundary term derived is valid not only for asymptotically AdS backgrounds, but also for more general asymptotics, including non-conformal branes and Improved Holographic QCD. In the second half of the paper, we apply the general result to Improved Holographic QCD with arbitrary dilaton potential. In particular, we derive the generalized Fefferman-Graham asymptotic expansions and provide a proof of the holographic Ward identities.
General proof of (maximum) entropy principle in Lovelock gravity
Cao, Li-Ming
2014-01-01
We consider a static self-gravitating perfect fluid system in Lovelock gravity theory. For a spacial region on the hypersurface orthogonal to static Killing vector, by the Tolman's law of temperature, the assumption of a fixed total particle number inside the spacial region, and all of the variations (of relevant fields) in which the induced metric and its first derivatives are fixed on the boundary of the spacial region, then with the help of the gravitational equations of the theory, we can prove a theorem says that the total entropy of the fluid in this region takes an extremum value. A converse theorem can also be obtained following the reverse process of our proof.
Cosmology for quadratic gravity in generalized Weyl geometry
Beltrán Jiménez, Jose; Heisenberg, Lavinia; Koivisto, Tomi S.
2016-04-01
A class of vector-tensor theories arises naturally in the framework of quadratic gravity in spacetimes with linear vector distortion. Requiring the absence of ghosts for the vector field imposes an interesting condition on the allowed connections with vector distortion: the resulting one-parameter family of connections generalises the usual Weyl geometry with polar torsion. The cosmology of this class of theories is studied, focusing on isotropic solutions wherein the vector field is dominated by the temporal component. De Sitter attractors are found and inhomogeneous perturbations around such backgrounds are analysed. In particular, further constraints on the models are imposed by excluding pathologies in the scalar, vector and tensor fluctuations. Various exact background solutions are presented, describing a constant and an evolving dark energy, a bounce and a self-tuning de Sitter phase. However, the latter two scenarios are not viable under a closer scrutiny.
General proof of (maximum) entropy principle in Lovelock gravity
Cao, Li-Ming; Xu, Jianfei
2015-02-01
We consider a static self-gravitating perfect fluid system in Lovelock gravity theory. For a spacial region on the hypersurface orthogonal to static Killing vector, by the Tolman's law of temperature, the assumption of a fixed total particle number inside the spacial region, and all of the variations (of relevant fields) in which the induced metric and its first derivatives are fixed on the boundary of the spacial region, then with the help of the gravitational and fluid equations of the theory, we can prove a theorem says that the total entropy of the fluid in this region takes an extremum value. A converse theorem can also be obtained following the reverse process of our proof. We also propose the definition of isolation quasilocally for the system and explain the physical meaning of the boundary conditions in the proof of the theorems.
Cosmology for quadratic gravity in generalized Weyl geometry
Jimenez, Jose Beltran; Koivisto, Tomi S
2016-01-01
A class of vector-tensor theories arises naturally in the framework of quadratic gravity in spacetimes with linear vector distortion. Requiring the absence of ghosts for the vector field imposes an interesting condition on the allowed connections with vector distortion: the resulting one-parameter family of connections generalises the usual Weyl geometry with polar torsion. The cosmology of this class of theories is studied, focusing on isotropic solutions wherein the vector field is dominated by the temporal component. De Sitter attractors are found and inhomogeneous perturbations around such backgrounds are analysed. In particular, further constraints on the models are imposed by excluding pathologies in the scalar, vector and tensor fluctuations. Various exact background solutions are presented, describing a constant and an evolving dark energy, a bounce and a self-tuning de Sitter phase. However, the latter two scenarios are not viable under a closer scrutiny.
Cosmology for quadratic gravity in generalized Weyl geometry
Energy Technology Data Exchange (ETDEWEB)
Jiménez, Jose Beltrán [CPT, Aix Marseille Université, UMR 7332,13288 Marseille (France); Heisenberg, Lavinia [Institute for Theoretical Studies, ETH Zurich,Clausiusstrasse 47, 8092 Zurich (Switzerland); Koivisto, Tomi S. [Nordita, KTH Royal Institute of Technology and Stockholm University,Roslagstullsbacken 23, 10691 Stockholm (Sweden)
2016-04-26
A class of vector-tensor theories arises naturally in the framework of quadratic gravity in spacetimes with linear vector distortion. Requiring the absence of ghosts for the vector field imposes an interesting condition on the allowed connections with vector distortion: the resulting one-parameter family of connections generalises the usual Weyl geometry with polar torsion. The cosmology of this class of theories is studied, focusing on isotropic solutions wherein the vector field is dominated by the temporal component. De Sitter attractors are found and inhomogeneous perturbations around such backgrounds are analysed. In particular, further constraints on the models are imposed by excluding pathologies in the scalar, vector and tensor fluctuations. Various exact background solutions are presented, describing a constant and an evolving dark energy, a bounce and a self-tuning de Sitter phase. However, the latter two scenarios are not viable under a closer scrutiny.
Smalley, L. L.
1983-01-01
The proper framework for testing Rastall's theory and its generalizations is in the case of non-negligible (i.e. discernible) gravitational effects such as gravity gradients. These theories have conserved integral four-momentum and angular momentum. The Nordtvedt effect then provides limits on the parameters which arise as the result of the non-zero divergence of the energy-momentum tensor.
Covariant Effective Field Theory of Gravity I: Formalism and Curvature expansion
Codello, Alessandro
2015-01-01
We construct the covariant effective field theory of gravity as an expansion in inverse powers of the Planck mass, identifying the leading and next-to-leading quantum corrections. We determine the form of the effective action for the cases of pure gravity with cosmological constant as well as gravity coupled to matter. By means of heat kernel methods we renormalize and compute the leading quantum corrections to quadratic order in a curvature expansion. The final effective action in our covariant formalism is generally non-local and can be readily used to understand the phenomenology on different spacetimes. In particular, we point out that on curved backgrounds the observable leading quantum gravitational effects are less suppressed than on Minkowski spacetime.
On the covariant formalism of the effective field theory of gravity and leading order corrections
DEFF Research Database (Denmark)
Codello, Alessandro; Jain, Rajeev Kumar
2016-01-01
We construct the covariant effective field theory of gravity as an expansion in inverse powers of the Planck mass, identifying the leading and next-to-leading quantum corrections. We determine the form of the effective action for the cases of pure gravity with cosmological constant as well...... as gravity coupled to matter. By means of heat kernel methods we renormalize and compute the leading quantum corrections to quadratic order in a curvature expansion. The final effective action in our covariant formalism is generally non-local and can be readily used to understand the phenomenology...... on different spacetimes. In particular, we point out that on curved backgrounds the observable leading quantum gravitational effects are less suppressed than on Minkowski spacetime....
On the covariant formalism of the effective field theory of gravity and leading order corrections
Codello, Alessandro; Jain, Rajeev Kumar
2016-11-01
We construct the covariant effective field theory of gravity as an expansion in inverse powers of the Planck mass, identifying the leading and next-to-leading quantum corrections. We determine the form of the effective action for the cases of pure gravity with cosmological constant as well as gravity coupled to matter. By means of heat kernel methods we renormalize and compute the leading quantum corrections to quadratic order in a curvature expansion. The final effective action in our covariant formalism is generally non-local and can be readily used to understand the phenomenology on different spacetimes. In particular, we point out that on curved backgrounds the observable leading quantum gravitational effects are less suppressed than on Minkowski spacetime.
A Unified Field Theory of Gravity, Electromagnetism, and the Yang-Mills Gauge Field
Directory of Open Access Journals (Sweden)
Suhendro I.
2008-01-01
Full Text Available In this work, we attempt at constructing a comprehensive four-dimensional unified field theory of gravity, electromagnetism, and the non-Abelian Yang-Mills gauge field in which the gravitational, electromagnetic, and material spin fields are unified as intrinsic geometric objects of the space-time manifold S4 via the connection, with the general- ized non-Abelian Yang-Mills gauge field appearing in particular as a sub-field of the geometrized electromagnetic interaction.
Group field theory as the 2nd quantization of Loop Quantum Gravity
Oriti, Daniele
2013-01-01
We construct a 2nd quantized reformulation of canonical Loop Quantum Gravity at both kinematical and dynamical level, in terms of a Fock space of spin networks, and show in full generality that it leads directly to the Group Field Theory formalism. In particular, we show the correspondence between canonical LQG dynamics and GFT dynamics leading to a specific GFT model from any definition of quantum canonical dynamics of spin networks. We exemplify the correspondence of dynamics in the specifi...
Rotating Killing horizons in generic F( R) gravity theories
Bhattacharya, Sourav
2016-10-01
We discuss various properties of rotating Killing horizons in generic F( R) theories of gravity in dimension four for spacetimes endowed with two commuting Killing vector fields. Assuming there is no curvature singularity anywhere on or outside the horizon, we construct a suitable (3+1)-foliation. We show that similar to Einstein's gravity, we must have T_{ab}k^ak^b=0 on the Killing horizon, where k^a is a null geodesic tangent to the horizon. For axisymmetric spacetimes, the effective gravitational coupling ˜ F'^{-1}(R) should usually depend upon the polar coordinate and hence need not necessarily be a constant on the Killing horizon. We prove that the surface gravity of such a Killing horizon must be a constant, irrespective of whether F'(R) is a constant there or not. We next apply these results to investigate some further basic features. In particular, we show that any hairy solution for the real massive vector field in such theories is clearly ruled out, as long as the potential of the scalar field generated in the corresponding Einstein's frame is a positive definite quantity.
A 4D gravity theory and G2-holonomy manifolds
Herfray, Yannick; Scarinci, Carlos; Shtanov, Yuri
2016-01-01
Bryant and Salamon gave a construction of metrics of G2 holonomy on the total space of the bundle of anti-self-dual (ASD) 2-forms over a 4-dimensional self-dual Einstein manifold. We generalise it by considering the total space of an SO(3) bundle (with fibers R^3) over a 4-dimensional base, with a connection on this bundle. We make essentially the same ansatz for the calibrating 3-form, but use the curvature 2-forms instead of the ASD ones. We show that the resulting 3-form defines a metric of G2 holonomy if the connection satisfies a certain second-order PDE. This is exactly the same PDE that arises as the field equation of a certain 4-dimensional gravity theory formulated as a diffeomorphism-invariant theory of SO(3) connections. Thus, every solution of this 4-dimensional gravity theory can be lifted to a G2-holonomy metric. Unlike all previously known constructions, the theory that we lift to 7 dimensions is not topological. Thus, our construction should give rise to many new metrics of G2 holonomy. We des...
General Relativity as AN ÆTHER Theory
Dupré, Maurice J.; Tipler, Frank J.
Most early twentieth century relativists — Lorentz, Einstein, Eddington, for examples — claimed that general relativity was merely a theory of the æther. We shall confirm this claim by deriving the Einstein equations using æther theory. We shall use a combination of Lorentz's and Kelvin's conception of the æther. Our derivation of the Einstein equations will not use the vanishing of the covariant divergence of the stress-energy tensor, but instead equate the Ricci tensor to the sum of the usual stress-energy tensor and a stress-energy tensor for the æther, a tensor based on Kelvin's æther theory. A crucial first step is generalizing the Cartan formalism of Newtonian gravity to allow spatial curvature, as conjectured by Gauss and Riemann. In essence, we shall show that the Einstein equations are a special case of Newtonian gravity coupled to a particular type of luminiferous æther. Our derivation of general relativity is simple, and it emphasizes how inevitable general relativity is, given the truth of Newtonian gravity and the Maxwell equations.
Algebraic Quantum Gravity (AQG) III. Semiclassical Perturbation Theory
Giesel, K
2006-01-01
In the two previous papers of this series we defined a new combinatorical approach to quantum gravity, Algebraic Quantum Gravity (AQG). We showed that AQG reproduces the correct infinitesimal dynamics in the semiclassical limit, provided one incorrectly substitutes the non -- Abelean group SU(2) by the Abelean group $U(1)^3$ in the calculations. The mere reason why that substitution was performed at all is that in the non -- Abelean case the volume operator, pivotal for the definition of the dynamics, is not diagonisable by analytical methods. This, in contrast to the Abelean case, so far prohibited semiclassical computations. In this paper we show why this unjustified substitution nevertheless reproduces the correct physical result: Namely, we introduce for the first time semiclassical perturbation theory within AQG (and LQG) which allows to compute expectation values of interesting operators such as the master constraint as a power series in $\\hbar$ with error control. That is, in particular matrix elements...
Curvature Singularity in f(R) Theories of Gravity
Dutta, Koushik; Patel, Avani
2015-01-01
Although f(R) modifications of late time cosmology is successful in explaining present cosmic acceleration, it is very difficult to simultaneously satisfy the fifth-force constraint. Even when the fifth-force constraint is satisfied, the effective scalar degree of freedom may move to a point (close to its minima) in the field space where the Ricci scalar diverges. We elucidate this point further with a specific example of f(R) gravity that incorporates several viable f(R) gravity models in the literature. In particular, we show that the nonlinear evolution of the scalar field in pressureless contracting dust can easily lead to the curvature singularity, making this theory unviable.
Fusion basis for lattice gauge theory and loop quantum gravity
Delcamp, Clement; Dittrich, Bianca; Riello, Aldo
2017-02-01
We introduce a new basis for the gauge-invariant Hilbert space of lattice gauge theory and loop quantum gravity in (2 + 1) dimensions, the fusion basis. In doing so, we shift the focus from the original lattice (or spin-network) structure directly to that of the magnetic (curvature) and electric (torsion) excitations themselves. These excitations are classified by the irreducible representations of the Drinfel'd double of the gauge group, and can be readily "fused" together by studying the tensor product of such representations. We will also describe in detail the ribbon operators that create and measure these excitations and make the quasi-local structure of the observable algebra explicit. Since the fusion basis allows for both magnetic and electric excitations from the onset, it turns out to be a precious tool for studying the large scale structure and coarse-graining flow of lattice gauge theories and loop quantum gravity. This is in neat contrast with the widely used spin-network basis, in which it is much more complicated to account for electric excitations, i.e. for Gauß constraint violations, emerging at larger scales. Moreover, since the fusion basis comes equipped with a hierarchical structure, it readily provides the language to design states with sophisticated multi-scale structures. Another way to employ this hierarchical structure is to encode a notion of subsystems for lattice gauge theories and (2 + 1) gravity coupled to point particles. In a follow-up work, we have exploited this notion to provide a new definition of entanglement entropy for these theories.
On the new version of generalized zwei-dreibein gravity
Energy Technology Data Exchange (ETDEWEB)
Setare, M.R., E-mail: rezakord@ipm.ir; Adami, H., E-mail: hamed.adami@yahoo.com
2015-11-12
In this paper we consider a generalization of zwei-dreibein gravity with a Chern–Simons term associated with a constraint term which fixes the torsion. We calculate the local degrees of freedom of this model using Hamiltonian analysis and show that our model has 3 propagating modes in comparison with the usual GZDG which has two bulk local degrees of freedom. Then looking at the quadratic Lagrangian, we determine that these propagating modes are 3 massive gravitons with different masses. Finally, we obtain AdS wave solution as an example solution for this model.
Mashhoon, Bahram
2017-01-01
Relativity theory is based on a postulate of locality, which means that the past history of the observer is not directly taken into account. This book argues that the past history should be taken into account. In this way, nonlocality---in the sense of history dependence---is introduced into relativity theory. The deep connection between inertia and gravitation suggests that gravity could be nonlocal, and in nonlocal gravity the fading gravitational memory of past events must then be taken into account. Along this line of thought, a classical nonlocal generalization of Einstein's theory of gravitation has recently been developed. A significant consequence of this theory is that the nonlocal aspect of gravity appears to simulate dark matter. According to nonlocal gravity theory, what astronomers attribute to dark matter should instead be due to the nonlocality of gravitation. Nonlocality dominates on the scale of galaxies and beyond. Memory fades with time; therefore, the nonlocal aspect of gravity becomes wea...
CDT-a entropic theory of quantum gravity
DEFF Research Database (Denmark)
Ambjørn, Jan; Görlich, A.; Jurkiewicz, J.
2010-01-01
High Energy Physics - Theory (hep-th); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Lattice (hep-lat)......High Energy Physics - Theory (hep-th); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Lattice (hep-lat)...
Generalized Uncertainty Principle and Analogue of Quantum Gravity in Optics
Braidotti, Maria Chiara; Conti, Claudio
2016-01-01
The design of optical systems capable of processing and manipulating ultra-short pulses and ultra-focused beams is highly challenging with far reaching fundamental technological applications. One key obstacle routinely encountered while implementing sub-wavelength optical schemes is how to overcome the limitations set by standard Fourier optics. A strategy to overcome these difficulties is to utilize the concept of generalized uncertainty principle (G-UP) that has been originally developed to study quantum gravity. In this paper we propose to use the concept of G-UP within the framework of optics to show that the generalized Schrodinger equation describing short pulses and ultra-focused beams predicts the existence of a minimal spatial or temporal scale which in turn implies the existence of maximally localized states. Using a Gaussian wavepacket with complex phase, we derive the corresponding generalized uncertainty relation and its maximally localized states. We numerically show that the presence of nonlin...
Millicharged dark matter in quantum gravity and string theory.
Shiu, Gary; Soler, Pablo; Ye, Fang
2013-06-14
We examine the millicharged dark matter scenario from a string theory perspective. In this scenario, kinetic and mass mixings of the photon with extra U(1) bosons are claimed to give rise to small electric charges, carried by dark matter particles, whose values are determined by continuous parameters of the theory. This seems to contradict folk theorems of quantum gravity that forbid the existence of irrational charges in theories with a single massless gauge field. By considering the underlying structure of the U(1) mass matrix that appears in type II string compactifications, we show that millicharges arise exclusively through kinetic mixing, and require the existence of at least two exactly massless gauge bosons.
Einstein's general theory of relativity with modern applications in cosmology
Grøn, Øyvind
2007-01-01
Many of us have experienced the same; fallen and broken something. Yet supposedly, gravity is the weakest of the fundamental forces; it is claimed to be 10-15 times weaker than electromagnetism. Still, every one of us has more or less had a personal relationship with gravity. Einstein’s General Theory of Relativity: With Modern Applications in Cosmology by Oyvind Gron and Sigbjorn Hervik is about gravity and the concept of gravity as Albert Einstein saw it- curved spaces, four-dimensional manifolds and geodesics. The book starts with the 1st principals of relativity and an introduction to Einstein’s field equations. Next up are the three classical tests of the relativity theory and an introduction to black holes. The book contains several topics not found in other textbooks, such as Kaluza-Klein theory, anisotropic models of the universe, and new developments involving brane cosmology. Gron and Hervik have included a part in the book called "Advanced Topics." These topics range from the very edge of resea...
Post-Newtonian parameter γ in generalized non-local gravity
Zhang, Xue; Wu, YaBo; Yang, WeiQiang; Zhang, ChengYuan; Chen, BoHai; Zhang, Nan
2017-10-01
We investigate the post-Newtonian parameter γ and derive its formalism in generalized non-local (GNL) gravity, which is the modified theory of general relativity (GR) obtained by adding a term m 2 n-2 R☐-n R to the Einstein-Hilbert action. Concretely, based on parametrizing the generalized non-local action in which gravity is described by a series of dynamical scalar fields ϕ i in addition to the metric tensor g μν, the post-Newtonian limit is computed, and the effective gravitational constant as well as the post-Newtonian parameters are directly obtained from the generalized non-local gravity. Moreover, by discussing the values of the parametrized post-Newtonian parameters γ, we can compare our expressions and results with those in Hohmann and Järv et al. (2016), as well as current observational constraints on the values of γ in Will (2006). Hence, we draw restrictions on the nonminimal coupling terms F̅ around their background values.
Kiefer, Claus
2012-01-01
The search for a quantum theory of the gravitational field is one of the great open problems in theoretical physics. This book presents a self-contained discussion of the concepts, methods and applications that can be expected in such a theory. The two main approaches to its construction - the direct quantisation of Einstein's general theory of relativity and string theory - are covered. Whereas the first attempts to construct a viable theory for the gravitational field alone, string theory assumes that a quantum theory of gravity will be achieved only through a unification of all the interactions. However, both employ the general method of quantization of constrained systems, which is described together with illustrative examples relevant for quantum gravity. There is a detailed presentation of the main approaches employed in quantum general relativity: path-integral quantization, the background-field method and canonical quantum gravity in the metric, connection and loop formulations. The discussion of stri...
Scalar ether theory of gravity a modification that seems needed
Arminjon, M
2004-01-01
The construction of the scalar theory based on the concept of gravity as Archimedes' thrust is briefly summarized, emphasizing the two (extreme) possibilities that result from this concept for the gravitational rod contraction: it can either occur in only one direction, or be isotropic. A modified equation for the scalar field is stated for the new, isotropic case. The reasons to consider this case are: i) it is almost as natural as the other case, and ii) it should avoid the violation of the weak equivalence principle, found for a small extended body with the directional contraction. The dynamical equation stays unchanged.
Scalar ether theory of gravity: a modification that seems needed
Arminjon, Mayeul
2004-01-01
The construction of the scalar theory based on the concept of gravity as Archimedes' thrust is briefly summarized, emphasizing the two (extreme) possibilities that result from this concept for the gravitational rod contraction: it can either occur in only one direction, or be isotropic. A modified equation for the scalar field is stated for the new, isotropic case. The reasons to consider this case are: i) it is almost as natural as the other case, and ii) it should avoid the violation of the...
Probing Theories of Gravity with Phase Space-Inferred Potentials of Galaxy Clusters
Stark, Alejo; Kern, Nicholas; Gifford, Daniel; Zhao, Gong-Bo; Li, Baojiu; Koyama, Kazuya; Nichol, Robert C
2016-01-01
Modified theories of gravity provide us with a unique opportunity to generate innovative tests of gravity. In Chameleon f(R) gravity, the gravitational potential differs from the weak-field limit of general relativity (GR) in a mass dependent way. We develop a probe of gravity which compares high mass clusters, where Chameleon effects are weak, to low mass clusters, where the effects can be strong. We utilize the escape velocity edges in the radius/velocity phase space to infer the gravitational potential profiles on scales of 0.3-1 virial radii. We show that the escape edges of low mass clusters are enhanced compared to GR, where the magnitude of the difference depends on the background field value |fR0|. We validate our probe using N-body simulations and simulated light cone galaxy data. For a DESI (Dark Energy Spectroscopic Instrument) Bright Galaxy Sample, including observational systematics, projection effects, and cosmic variance, our test can differentiate between GR and Chameleon f(R) gravity models, ...
Rotating Killing horizons in generic $F(R)$ gravity theories
Bhattacharya, Sourav
2016-01-01
We discuss various properties of rotating Killing horizons in generic non-singular $F(R)$ theories of gravity in dimension four for spacetimes endowed with two commuting Killing vector fields. By constructing a suitable $(3+1)$-foliation, we show that similar to Einstein's gravity, we must have $T_{ab}k^ak^b=0$ on the Killing horizon, where $k^a$ is a null geodesic tangent to the horizon. For axisymmetric spacetimes, the effective gravitational coupling $\\sim\\,F'^{-1}(R)$ should usually depend upon the polar coordinate and hence need not necessarily be a constant on the Killing horizon. We prove that the surface gravity of such a Killing horizon must be a constant, irrespective of whether $F'(R)$ is a constant there or not. We next use these results to derive some simple corollaries. In particular, we point out that the no hair theorem for the real massive vector field need not necessarily hold for a generic $F(R)$, unless some additional condition is satisfied.
Probing scalar tensor theories for gravity in Redshift-Space
Sabiu, Cristiano G; Llinares, Claudio; Park, Changbom
2016-01-01
We present measurements of the spatial clustering statistics in redshift space of various scalar field modified gravity simulations. We utilise the two-point and the three-point correlation functions to quantify the spatial distribution of dark matter halos within these simulations and thus discern between the models. We compare $\\Lambda$CDM simulations to various modified gravity scenarios and find consistency with previous work in terms of 2-point statistics in real and redshift-space. However using higher order statistics such as the three-point correlation function in redshift space we find significant deviations from $\\Lambda$CDM hinting that higher order statistics may prove to be a useful tool in the hunt for deviations from General Relativity.
New Black Hole Solutions in Brans-Dicke Theory of Gravity
Kim, H
1999-01-01
Existence check of non-trivial, stationary axisymmetric black hole solutions in Brans-Dicke theory of gravity in different direction from those of Penrose, Thorne and Dykla, and Hawking is performed. Namely, working directly with the known explicit spacetime solutions in Brans-Dicke theory, it is found that non-trivial Kerr-Newman-type black hole solutions different from general relativistic solutions could occur for the generic Brans-Dicke parameter values -5/2\\leq ømega <-3/2. Finally, issues like whether these black holes can really arise in nature are discussed carefully.
Gravity, black holes and the very early Universe an introduction to general relativity and cosmology
Chow, Tai L
2008-01-01
In the early 1900s, Albert Einstein formulated two theories that would forever change the landscape of physics: the Special Theory of Relativity and the General Theory of Relativity. By 1925, quantum mechanics had been born out of the dissection of these two theories, and shortly after that, relativistic quantum field theory. We now had in place some important ties between the laws of physics and the types of particle interactions the new physics was uncovering. Gravity is one of the four types of forces that are found throughout the universe. In fact, although it is a relatively weak force, it operates at huge distances, and so must be accounted for in any cosmological system. Unfortunately, gravity continues to defy our neat categorization of how all the forces in nature work together. Professor Tai Chow, from the California State University at Stanislaus in Turlock, lays out for us the basic ideas of Einstein, including his law of gravitation, explains the physics behind black holes, and weaves into this a...
Setare, M. R.; Adami, H.
2016-01-01
In the first order formalism of gravity theories, there are some theories which are not Lorentz-diffeomorphism covariant. In the framework of such theories we cannot apply the method of conserved charge calculation used in Lorentz-diffeomorphism covariant theories. In this paper we firstly introduce the total variation of a quantity due to an infinitesimal Lorentz-diffeomorphism transformation. Secondly, in order to obtain the conserved charges of Lorentz-diffeomorphism non-covariant theories, we extend the Tachikawa method [1]. This extension includes not only Lorentz gauge transformation but also the diffeomorphism. We apply this method to the Chern-Simons-like theories of gravity (CSLTG) and obtain a general formula for the entropy of black holes in those theories. Finally, some examples on CSLTG are provided and the entropy of the BTZ black hole is calculated in the context of the examples.
Directory of Open Access Journals (Sweden)
M.R. Setare
2016-01-01
Full Text Available In the first order formalism of gravity theories, there are some theories which are not Lorentz-diffeomorphism covariant. In the framework of such theories we cannot apply the method of conserved charge calculation used in Lorentz-diffeomorphism covariant theories. In this paper we firstly introduce the total variation of a quantity due to an infinitesimal Lorentz-diffeomorphism transformation. Secondly, in order to obtain the conserved charges of Lorentz-diffeomorphism non-covariant theories, we extend the Tachikawa method [1]. This extension includes not only Lorentz gauge transformation but also the diffeomorphism. We apply this method to the Chern–Simons-like theories of gravity (CSLTG and obtain a general formula for the entropy of black holes in those theories. Finally, some examples on CSLTG are provided and the entropy of the BTZ black hole is calculated in the context of the examples.
Energy Technology Data Exchange (ETDEWEB)
Setare, M.R., E-mail: rezakord@ipm.ir; Adami, H., E-mail: hamed.adami@yahoo.com
2016-01-15
In the first order formalism of gravity theories, there are some theories which are not Lorentz-diffeomorphism covariant. In the framework of such theories we cannot apply the method of conserved charge calculation used in Lorentz-diffeomorphism covariant theories. In this paper we firstly introduce the total variation of a quantity due to an infinitesimal Lorentz-diffeomorphism transformation. Secondly, in order to obtain the conserved charges of Lorentz-diffeomorphism non-covariant theories, we extend the Tachikawa method [1]. This extension includes not only Lorentz gauge transformation but also the diffeomorphism. We apply this method to the Chern–Simons-like theories of gravity (CSLTG) and obtain a general formula for the entropy of black holes in those theories. Finally, some examples on CSLTG are provided and the entropy of the BTZ black hole is calculated in the context of the examples.
Setare, M R
2016-01-01
In the first order formalism of gravity theories, may be exist some theories which are not Lorentz-difeomorphism covariant so for such theories a method for which one can calculate conserved charges of Lorentz-difeomorphism covariant theories are useless. In this letter we introduce the total variation of a quantity due to an infinitesimal Lorentz-diffeomorphism transformation. Then using this concept, in order to obtain the conserved charges in Lorentz-diffeomorphism non-covariant theories, we extend the Tachikawa's method \\cite{3} so that it includes Lorentz gauge transformation in addition to diffeomorphism. We apply this method on the Chern-Simons-like theories of gravity and we find out a general formula for the entropy of black holes in those theories. Eventually, we consider some examples and calculate entropy of the BTZ black hole in the context of this examples.
Perturbations of single-field inflation in modified gravity theory
Directory of Open Access Journals (Sweden)
Taotao Qiu
2015-05-01
Full Text Available In this paper, we study the case of single field inflation within the framework of modified gravity theory where the gravity part has an arbitrary form f(R. Via a conformal transformation, this case can be transformed into its Einstein frame where it looks like a two-field inflation model. However, due to the existence of the isocurvature modes in such a multi-degree-of-freedom (m.d.o.f. system, the (curvature perturbations are not equivalent in two frames, so despite of its convenience, it is illegal to treat the perturbations in its Einstein frame as the “real” ones as we always do for pure f(R theory or single field with nonminimal coupling. Here by pulling the results of curvature perturbations back into its original Jordan frame, we show explicitly the power spectrum and spectral index of the perturbations in the Jordan frame, as well as how it differs from the Einstein frame. We also fit our results with the newest Planck data. Since there is large parameter space in these models, we show that it is easy to fit the data very well.
Fusion basis for lattice gauge theory and loop quantum gravity
Delcamp, Clement; Riello, Aldo
2016-01-01
We introduce a new basis for the gauge--invariant Hilbert space of lattice gauge theory and loop quantum gravity in $(2+1)$ dimensions, the fusion basis. In doing so, we shift the focus from the original lattice (or spin--network) structure directly to that of the magnetic (curvature) and electric (torsion) excitations themselves. These excitations are classified by the irreducible representations of the Drinfel'd double of the gauge group, and can be readily "fused" together by studying the tensor product of such representations. We will also describe in detail the ribbon operators that create and measure these excitations and make the quasi--local structure of the observable algebra explicit. Since the fusion basis allows for both magnetic and electric excitations from the onset, it turns out to be a precious tool for studying the large scale structure and coarse--graining flow of lattice gauge theories and loop quantum gravity. This is in neat contrast with the widely used spin--network basis, in which it ...
Moyal deformations of Clifford gauge theories of gravity
Castro, Carlos
2016-12-01
A Moyal deformation of a Clifford Cl(3, 1) Gauge Theory of (Conformal) Gravity is performed for canonical noncommutativity (constant Θμν parameters). In the very special case when one imposes certain constraints on the fields, there are no first-order contributions in the Θμν parameters to the Moyal deformations of Clifford gauge theories of gravity. However, when one does not impose constraints on the fields, there are first-order contributions in Θμν to the Moyal deformations in variance with the previous results obtained by other authors and based on different gauge groups. Despite that the generators of U(2, 2),SO(4, 2),SO(2, 3) can be expressed in terms of the Clifford algebra generators this does not imply that these algebras are isomorphic to the Clifford algebra. Therefore one should not expect identical results to those obtained by other authors. In particular, there are Moyal deformations of the Einstein-Hilbert gravitational action with a cosmological constant to first-order in Θμν. Finally, we provide a mechanism which furnishes a plausible cancellation of the huge vacuum energy density.
Gheorghiu, Tamara; Vacaru, Olivia; Vacaru, Sergiu I
2016-01-01
We study geometric relativistic flow and Ricci soliton equations which (for respective nonholonomic constraints and self-similarity conditions) are equivalent to the gravitational field equations of $R^2$ gravity and/or to the Einstein equations with scalar field in general relativity, GR. Perelman's functionals are generalized for modified gravity theories, MGTs, which allows to formulate an analogous statistical thermodynamics for geometric flows and Ricci solitons. There are constructed and analyzed generic off-diagonal black ellipsoid, black hole and solitonic exact solutions in MGTs and GR encoding geometric flow evolution scenarios and nonlinear parametric interactions. Such new classes of solutions in MGTs can be with polarized and/or running constants, nonholonomically deformed horizons and/or imbedded self-consistently into solitonic backgrounds. They exist also in GR as generic off-diagonal vacuum configurations with effective cosmological constant and/or mimicking effective scalar field interaction...
Serendipitous discoveries in nonlocal ghost-free gravity theory: dark energy and dark matter
Barvinsky, Andrei O
2011-01-01
We present a class of generally covariant nonlocal gravity models briefly reported in arXiv:1107.1463, which have a flat-space general relativistic (GR) limit and also possess a stable de Sitter (dS) or Anti-de Sitter (AdS) background with an arbitrary value of its cosmological constant. The nonlocal action of the theory is formulated in the Euclidean signature spacetime and is understood as an approximation to the quantum effective action (generating functional of one-particle irreducible diagrams) originating from fundamental quantum gravity theory. Using the known relation between the Schwinger-Keldysh technique for quantum expectation values and the Euclidean quantum field theory we derive from this action the {\\em causal} effective equations of motion for mean value of the metric field in the physical Lorentzian-signature spacetime. Thus we show that the (A)dS background of the theory carries as free propagating modes massless gravitons having two polarizations identical to those of the Einstein theory w...
Holographic thermalization and generalized Vaidya-AdS solutions in massive gravity
Hu, Ya-Peng; Zeng, Xiao-Xiong; Zhang, Hai-Qing
2017-02-01
We investigate the effect of massive graviton on the holographic thermalization process. Before doing this, we first find out the generalized Vaidya-AdS solutions in the de Rham-Gabadadze-Tolley (dRGT) massive gravity by directly solving the gravitational equations. Then, we study the thermodynamics of these Vaidya-AdS solutions by using the Misner-Sharp energy and unified first law, which also shows that the massive gravity is in a thermodynamic equilibrium state. Moreover, we adopt the two-point correlation function at equal time to explore the thermalization process in the dual field theory, and to see how the graviton mass parameter affects this process from the viewpoint of AdS/CFT correspondence. Our results show that the graviton mass parameter will increase the holographic thermalization process.
Holographic Thermalization and Generalized Vaidya-AdS Solutions in Massive Gravity
Hu, Ya-Peng; Zhang, Hai-Qing
2016-01-01
We investigate the effect of massive graviton on the holographic thermalization process. Before doing this, we first find out the generalized Vaidya-AdS solutions in the de Rham-Gabadadze-Tolley (dRGT) massive gravity by directly solving the gravitational equations. Then, we study the thermodynamics of these Vaidya-AdS solutions by using the Minsner-Sharp energy and unified first law, which also shows that the massive gravity is in a thermodynamic equilibrium state. Moreover, we adopt the two-point correlation function at equal time to explore the thermalization process in the dual field theory, and to see how the graviton mass parameter affects this process from the viewpoint of AdS/CFT correspondence. Our results show that the graviton mass parameter will increase the holographic thermalization process.
Holographic thermalization and generalized Vaidya-AdS solutions in massive gravity
Directory of Open Access Journals (Sweden)
Ya-Peng Hu
2017-02-01
Full Text Available We investigate the effect of massive graviton on the holographic thermalization process. Before doing this, we first find out the generalized Vaidya-AdS solutions in the de Rham–Gabadadze–Tolley (dRGT massive gravity by directly solving the gravitational equations. Then, we study the thermodynamics of these Vaidya-AdS solutions by using the Misner–Sharp energy and unified first law, which also shows that the massive gravity is in a thermodynamic equilibrium state. Moreover, we adopt the two-point correlation function at equal time to explore the thermalization process in the dual field theory, and to see how the graviton mass parameter affects this process from the viewpoint of AdS/CFT correspondence. Our results show that the graviton mass parameter will increase the holographic thermalization process.
Formalism locality in quantum theory and quantum gravity
Hardy, Lucien
2008-01-01
We expect a theory of Quantum Gravity to be both probabilistic and have indefinite causal structure. Indefinite causal structure poses particular problems for theory formulation since many of the core ideas used in the usual approaches to theory construction depend on having definite causal structure. For example, the notion of a state across space evolving in time requires that we have some definite causal structure so we can define a state on a space-like hypersurface. We will see that many of these problems are mitigated if we are able to formulate the theory in a "formalism local" (or F-local) fashion. A formulation of a physical theory is said to be F-local if, in making predictions for any given arbitrary space-time region, we need only refer to mathematical objects pertaining to that region. This is a desirable property both on the grounds of efficiency and since, if we have indefinite causal structure, it is not clear how to select some other space-time region on which our calculations may depend. The...
Variational approach to gravity field theories from Newton to Einstein and beyond
Vecchiato, Alberto
2017-01-01
This book offers a detailed and stimulating account of the Lagrangian, or variational, approach to general relativity and beyond. The approach more usually adopted when describing general relativity is to introduce the required concepts of differential geometry and derive the field and geodesic equations from purely geometrical properties. Demonstration of the physical meaning then requires the weak field approximation of these equations to recover their Newtonian counterparts. The potential downside of this approach is that it tends to suit the mathematical mind and requires the physicist to study and work in a completely unfamiliar environment. In contrast, the approach to general relativity described in this book will be especially suited to physics students. After an introduction to field theories and the variational approach, individual sections focus on the variational approach in relation to special relativity, general relativity, and alternative theories of gravity. Throughout the text, solved exercis...
A simplified approach to general scalar-tensor theories
Energy Technology Data Exchange (ETDEWEB)
Bloomfield, Jolyon, E-mail: jkb84@cornell.edu [Center for Radiophysics and Space Research, Cornell University, Ithaca, New York, 14853 (United States)
2013-12-01
The most general covariant action describing gravity coupled to a scalar field with only second order equations of motion, Horndeski's theory (also known as ''Generalized Galileons''), provides an all-encompassing model in which single scalar dark energy models may be constrained. However, the generality of the model makes it cumbersome to manipulate. In this paper, we demonstrate that when considering linear perturbations about a Friedmann-Robertson-Walker background, the theory is completely specified by only six functions of time, two of which are constrained by the background evolution. We utilise the ideas of the Effective Field Theory of Inflation/Dark Energy to explicitly construct these six functions of time in terms of the free functions appearing in Horndeski's theory. These results are used to investigate the behavior of the theory in the quasistatic approximation. We find that only four functions of time are required to completely specify the linear behavior of the theory in this limit, which can further be reduced if the background evolution is fixed. This presents a significantly reduced parameter space from the original presentation of Horndeski's theory, giving hope to the possibility of constraining the parameter space. This work provides a cross-check for previous work on linear perturbations in this theory, and also generalizes it to include spatial curvature.
Generalized conservation laws in non-local field theories
Kegeles, Alexander; Oriti, Daniele
2016-04-01
We propose a geometrical treatment of symmetries in non-local field theories, where the non-locality is due to a lack of identification of field arguments in the action. We show that the existence of a symmetry of the action leads to a generalized conservation law, in which the usual conserved current acquires an additional non-local correction term, obtaining a generalization of the standard Noether theorem. We illustrate the general formalism by discussing the specific physical example of complex scalar field theory of the type describing the hydrodynamic approximation of Bose-Einstein condensates. We expect our analysis and results to be of particular interest for the group field theory formulation of quantum gravity.
Topological M-theory as Unification of Form Theories of Gravity
Dijkgraaf, R; Neitzke, A; Vafa, C; Dijkgraaf, Robbert; Gukov, Sergei; Neitzke, Andrew; Vafa, Cumrun
2004-01-01
We introduce a notion of topological M-theory and argue that it provides a unification of form theories of gravity in various dimensions. Its classical solutions involve G_2 holonomy metrics on 7-manifolds, obtained from a topological action for a 3-form gauge field introduced by Hitchin. We show that by reductions of this 7-dimensional theory one can classically obtain 6-dimensional topological A and B models, the topological sector of loop quantum gravity in 4 dimensions, and Chern-Simons gravity in 3 dimensions. We also find that the 7-dimensional M-theory perspective sheds some light on the fact that the topological string partition function is a wavefunction, as well as on S-duality between the A and B models. The degrees of freedom of the A and B models appear as conjugate variables in the 7-dimensional theory. Finally, from the topological M-theory perspective we find hints of an intriguing holographic link between non-supersymmetric Yang-Mills in 4 dimensions and A model topological strings on twistor...
Motivations for anti-gravity in general relativity
Energy Technology Data Exchange (ETDEWEB)
Chardin, G. [CEA Centre d`Etudes de Saclay, 91 - Gif-sur-Yvette (France). Dept. d`Astrophysique, de la Physique des Particules, de la Physique Nucleaire et de l`Instrumentation Associee
1996-05-01
Arguments are presented showing that it is natural to interpret the negative mass part of the Kerr solution as representing the geometry experienced by antimatter. The C, P and T discrete transformations are considered for this geometry. The C and T properties of the proposed identification are found to be in agreement with the usual representation of antimatter. In addition, a property of perfect stigmatism through Kerr wormholes which allows general relativity to mimic anti-gravity is conjectured. Kerr wormholes would then act as `super-mirrors` reversing the C, P and T images of an object seen through it. This interpretation is subjected to several experimental tests and able to provide an explanation, without any free parameter, of the `CP`-violation observed in the neutral kaon system. (K.A.). 37 refs.
Cosmological perturbations of unimodular gravity and general relativity are identical
Basak, Abhishek; Fabre, Ophélia; Shankaranarayanan, S.
2016-10-01
Unimodular gravity (UG) is a restricted version of general relativity (GR) in which the variation of the metric determinant is set to zero and the field equations are given by the trace-free part of the full Einstein equations. The background equations in UG and GR are identical. It was recently claimed that the first order contribution in the temperature fluctuations of the Cosmic Microwave Background (CMB) in UG is different from GR. In this work, we calculate the first order perturbation equations in UG and show that the Sachs-Wolfe effect in UG, in terms of gauge invariant variables, is identical to GR. We also show that the second order perturbation equation of Mukhanov-Sasaki variable in UG, is identical to GR. The only difference comes from the gauge choices due the constraint on the metric determinant. Hence, UG and GR are identical and indistinguishable in CMB data on large scales.
Mathematical Validity of the f(R) Theory of Modified Gravity
LeFloch, Philippe G
2014-01-01
We establish a well-posedness theory for the f(R) theory of modified gravity, which is a generalization of Einstein's theory of gravitation. The scalar curvature R of the spacetime, which arises in the integrand of the Einstein-Hilbert functional, is replaced by a function f=f(R). The field equations involve up to fourth-order derivatives of the spacetime metric, and the challenge is to understand the structure of these high-order terms. We propose a formulation of the initial value problem in modified gravity when the initial data are prescribed on a hypersurface. In addition to the induced metric and second fundamental form of the initial slice and the initial matter content, an initial data set must also provide the spacetime scalar curvature and its time-derivative. We introduce an augmented conformal formulation, as we call it, in which the spacetime curvature is an independent variable. In the so-called wave gauge, the field equations of modified gravity reduce a coupled system of nonlinear wave-Klein-G...
Constraining alternative theories of gravity using GW$150914$ and GW$151226$
De Laurentis, Mariafelicia; Bovard, Luke; Ahmedov, Bobomurat; Abdujabbarov, Ahmadjon
2016-01-01
The recently reported gravitational wave events GW$150914$ and GW$151226$ caused by the mergers of binary black holes [arXiv:1602.03841],[arXiv:1606.04855],[arXiv:1606.04856] provide a formidable way to set constraints on alternative metric theories of gravity in the strong field regime. In this paper, we develop an approach where an arbitrary theory of gravity can be parametrised by an effective coupling $G_{eff}$ and an effective gravitational potential $\\Phi(r)$. The standard Newtonian limit of General Relativity is recovered as soon as $G_{eff}\\rightarrow G_N$ and $\\Phi(r)\\rightarrow \\Phi_{N}$. The upper bound on the graviton mass and the gravitational interaction length, reported by the LIGO-VIRGO collaboration, can be directly recast in terms of the parameters of the theory which allows an analysis where the gravitational wave frequency modulation sets constraints on the range of possible alternative models of gravity. Numerical results based on published parameters for the binary black hole mergers are...
Theoretical frameworks for testing relativistic gravity. 5: Post-Newtonian limit of Rosen's theory
Lee, D. L.; Caves, C. M.
1974-01-01
The post-Newtonian limit of Rosen's theory of gravity is evaluated and is shown to be identical to that of general relativity, except for the PPN parameter alpha sub 2, which is related to the difference in propagation speeds for gravitational and electromagnetic waves. Both the value of alpha sub 2 and the value of the Newtonian gravitational constant depend on the present cosmological structure of the Universe. If the cosmological structure has a specific but presumably special form, the Newtonian gravitational constant assumes its current value, alpha sub 2 is zero, the post-Newtonian limit of Rosen's theory is identical to that of general relativity--and standard solar system experiments cannot distinguish between the two theories.
Theoretical frameworks for testing relativistic gravity. V - Post-Newtonian limit of Rosen's theory
Lee, D. L.; Ni, W.-T.; Caves, C. M.; Will, C. M.
1976-01-01
The post-Newtonian limit of Rosen's theory of gravity is evaluated and is shown to be identical to that of general relativity, except for the post-Newtonian parameter alpha sub 2 (which is related to the difference in propagation speeds for gravitational and electromagnetic waves). Both the value of alpha sub 2 and the value of the Newtonian gravitational constant depend on the present cosmological structure of the Universe. If the cosmological structure has a specific (but presumably special) form, the Newtonian gravitational constant assumes its current value, alpha sub 2 is zero, the post-Newtonian limit of Rosen's theory is identical to that of general relativity - and standard solar system experiments cannot distinguish between the two theories.
General Theory of Relativity: Will It Survive the Next Decade?
Bertolami, Orfeu; Paramos, Jorge; Turyshev, Slava G.
2006-01-01
The nature of gravity is fundamental to our understanding of our own solar system, the galaxy and the structure and evolution of the Universe. Einstein's general theory of relativity is the standard model that is used for almost ninety years to describe gravitational phenomena on these various scales. We review the foundations of general relativity, discuss the recent progress in the tests of relativistic gravity, and present motivations for high-accuracy gravitational experiments in space. We also summarize the science objectives and technology needs for the laboratory experiments in space with laboratory being the entire solar system. We discuss the advances in our understanding of fundamental physics anticipated in the near future and evaluate discovery potential for the recently proposed gravitational experiments.
Generalized Liquid Film Atomization Theory
Institute of Scientific and Technical Information of China (English)
HeraldoS.Couto; DemetrioBastos－Netto
2000-01-01
The increase of the fuel burning area required by most practical combustion processes in order to guarantee the minimum energy density rate release for their start up and operation is normally achieved by the proper choice among several existing types of atomizers.For instance.impinging and multi-impinging jets atomizers are used in rocket combustion chambers.while splash-plate atomizers find their use when wall film cooling is required.Pressure swirl atomizers,either of simplex or duplex kind,along with Y-jet or SPider Jet atomizers are used in industrial applications and in turbine combustion chambers.Notice.however,that all the types of atomizing devices listed above have one point in common:they are of pre-filming kind.i.e.,befor the droplet spray is generated,a liquid film is formed.This liquid film is broken into unstable ligaments which contract under the action of surface tension forming the droplets.Once the film thickness is estimated.the droplets'SMD(Sauter Mean Diameter)can be calculated.yielding a crucial prameter for the combustion chamber design.However,although this mechanism of droplet fromation has been under study for several decades.most of the available results.are based upon experimental data.valid for a special type of atomizer under the given sepcific conditions only.This work offers a generalized theory for theoretically estimating the SMD of sprays generated by liquid pre-filming atomizers in gereral.
Quantum fields in the non-perturbative regime. Yang-Mills theory and gravity
Energy Technology Data Exchange (ETDEWEB)
Eichhorn, Astrid
2011-09-06
In this thesis we study candidates for fundamental quantum field theories, namely non-Abelian gauge theories and asymptotically safe quantum gravity. Whereas the first ones have a stronglyinteracting low-energy limit, the second one enters a non-perturbative regime at high energies. Thus, we apply a tool suited to the study of quantum field theories beyond the perturbative regime, namely the Functional Renormalisation Group. In a first part, we concentrate on the physical properties of non-Abelian gauge theories at low energies. Focussing on the vacuum properties of the theory, we present an evaluation of the full effective potential for the field strength invariant F{sub {mu}}{sub {nu}}F{sup {mu}}{sup {nu}} from non-perturbative gauge correlation functions and find a non-trivial minimum corresponding to the existence of a dimension four gluon condensate in the vacuum. We also relate the infrared asymptotic form of the {beta} function of the running background-gauge coupling to the asymptotic behavior of Landau-gauge gluon and ghost propagators and derive an upper bound on their scaling exponents. We then consider the theory at finite temperature and study the nature of the confinement phase transition in d = 3+1 dimensions in various non-Abelian gauge theories. For SU(N) with N= 3,..,12 and Sp(2) we find a first-order phase transition in agreement with general expectations. Moreover our study suggests that the phase transition in E(7) Yang-Mills theory also is of first order. Our studies shed light on the question which property of a gauge group determines the order of the phase transition. In a second part we consider asymptotically safe quantum gravity. Here, we focus on the Faddeev-Popov ghost sector of the theory, to study its properties in the context of an interacting UV regime. We investigate several truncations, which all lend support to the conjecture that gravity may be asymptotically safe. In a first truncation, we study the ghost anomalous dimension
Discrete gravity as a local theory of the Poincare group in the first-order formalism
Energy Technology Data Exchange (ETDEWEB)
Gionti, Gabriele [Vatican Observatory Research Group, Steward Observatory, 933 North Cherry Avenue, University of Arizona, Tucson, AZ 85721 (United States); Specola Vaticana, V-00120 Citta Del Vaticano (Vatican City State, Holy See,)
2005-10-21
A discrete theory of gravity, locally invariant under the Poincare group, is considered as in a companion paper. We define a first-order theory, in the sense of Palatini, on the metric-dual Voronoi complex of a simplicial complex. We follow the same spirit as the continuum theory of general relativity in the Cartan formalism. The field equations are carefully derived taking in account the constraints of the theory. They look very similar to first-order Einstein continuum equations in the Cartan formalism. It is shown that in the limit of small deficit angles these equations have Regge calculus, locally, as the only solution. A quantum measure is easily defined which does not suffer the ambiguities of Regge calculus, and a coupling with fermionic matter is easily introduced.
Mendes, Raissa F P
2016-01-01
Scalar-tensor theories of gravity are extensions of General Relativity (GR) including an extra, nonminimally coupled scalar degree of freedom. A wide class of these theories, albeit indistinguishable from GR in the weak field regime, predicts a radically different phenomenology for neutron stars, due to a nonperturbative, strong-field effect referred to as spontaneous scalarization. This effect is known to occur in theories where the effective linear coupling $\\beta_0$ between the scalar and matter fields is sufficiently negative, i.e. $\\beta_0 \\lesssim -4.35$, and has been strongly constrained by pulsar timing observations. In the test-field approximation, spontaneous scalarization manifests itself as a tachyonic-like instability. Recently, it was argued that, in theories where $\\beta_0>0$, a similar instability would be triggered by sufficiently compact neutron stars obeying realistic equations of state. In this work we investigate the endstate of this instability for some representative coupling functions ...
Unification of General Relativity with Quantum Field Theory
Institute of Scientific and Technical Information of China (English)
NI Jun
2011-01-01
In the frame of quantum field theory, instead of using the action principle, we deduce the Einstein equation from purely the general covariant principle and the homogeneity of spacetime. The Einstein equation is shown to be the gauge equation to guarantee the local symmetry of spacetime translation. Gravity is an apparent force due to the curvature of spacetime resulted from the conservation of energy-momentum. In the action of quantum field theory, only electroweak-strong interactions should be considered with the curved spacetime metric determined by the Einstein equation.%In the frame of quantum field theory,instead of using the action principle,we deduce the Einstein equation trom purely the general covariant principle and the homogeneity of spacetime.The Einstein equation is shown to be the gauge equation to guarantee the local symmetry of spacetime translation.Gravity is an apparent force due to the curvature of spacetime resulted from the conservation of energy-momentum.In the action of quantum field theory,only electroweak-strong interactions should be considered with the curved spacetime metric determined by the Einstein equation.An unified physical theory of all interactions is a long pursued goal for physicists.The unification of electricity and magnetism by Maxwell was a great step in this direction.It is believed that in nature,there are four types of fundamental interactions:the electromagnetic interaction,weak interaction,strong interaction and gravity.Now the electromagnetic,weak and strong interactions are unified using the so-called standard model,[1] based on the Yang-Mills gauge field theory.[2] However,researchers are still not be able to unify gravitation with the other three interactions.
Energy Technology Data Exchange (ETDEWEB)
Faller, Sven [Universitaet Siegen, Theoretische Physik 1 (Germany)
2008-07-01
In the last years a lot of papers were published treating general relativity as an effective field theory. We are dealing with general relativity and the combination of general relativity and scalar QED as effective field theories. For effective field theories the quantization is well known therefore we are able to quantize general relativity and the combination of general relativity and scalar QED. The vertex rules can be extracted from the action and the non-analytical contributions to the 1-loop scattering matrix of scalars and charged scalars are calculated in the non-relativistic limit. The non-analytical parts of the scattering amplitudes yield the long range, low energy, leading quantum corrections. From the general relativity as an effective field theory the leading quantum corrections to the Newtonian gravity is constructed. General relativity combined with scalar QED yield the post-Newtonian and quantum corrections to the two-particle non-relativistic scattering matrix potential for charged scalar particles. The difference to other publications is finally discussed.
Standard general relativity from Chern-Simons gravity
Energy Technology Data Exchange (ETDEWEB)
Izaurieta, F. [Departamento de Matematica y Fisica Aplicadas, Universidad, Catolica de la Santisima Concepcion, Alonso de Rivera 2850, Concepcion (Chile); Minning, P. [Departamento de Fisica, Universidad de Concepcion, Casilla 160-C, Concepcion (Chile); Perez, A. [Departamento de Fisica, Universidad de Concepcion, Casilla 160-C, Concepcion (Chile); Max Planck Institut fuer Gravitationsphysik, Albert Einstein, Institut. Am Muehlenberg1, D-14476 Golm bei Potsdam (Germany); Rodriguez, E. [Departamento de Matematica y Fisica Aplicadas, Universidad, Catolica de la Santisima Concepcion, Alonso de Rivera 2850, Concepcion (Chile); Salgado, P. [Departamento de Fisica, Universidad de Concepcion, Casilla 160-C, Concepcion (Chile)], E-mail: pasalgad@udec.cl
2009-07-13
Chern-Simons models for gravity are interesting because they provide a truly gauge-invariant action principle in the fiber-bundle sense. So far, their main drawback has largely been its perceived remoteness from standard General Relativity, based on the presence of higher powers of the curvature in the Lagrangian (except, remarkably, for three-dimensional spacetime). Here we report on a simple model that suggests a mechanism by which standard General Relativity in five-dimensional spacetime may indeed emerge at a special critical point in the space of couplings, where additional degrees of freedom and corresponding 'anomalous' Gauss-Bonnet constraints drop out from the Chern-Simons action. To achieve this goal, both the Lie algebra g and the symmetric g-invariant tensor that define the Chern-Simons Lagrangian are constructed by means of the Lie algebra S-expansion method with a suitable finite Abelian semigroup S. The results are generalized to arbitrary odd dimensions, and the possible extension to the case of eleven-dimensional supergravity is briefly discussed.
Algebraic K-theory of generalized schemes
DEFF Research Database (Denmark)
Anevski, Stella Victoria Desiree
Nikolai Durov has developed a generalization of conventional scheme theory in which commutative algebraic monads replace commutative unital rings as the basic algebraic objects. The resulting geometry is expressive enough to encompass conventional scheme theory, tropical algebraic geometry...
Algebraic K-theory of generalized schemes
DEFF Research Database (Denmark)
Anevski, Stella Victoria Desiree
Nikolai Durov has developed a generalization of conventional scheme theory in which commutative algebraic monads replace commutative unital rings as the basic algebraic objects. The resulting geometry is expressive enough to encompass conventional scheme theory, tropical algebraic geometry...
Theory of Quantum Gravity Beyond Einstein and Space-time Dynamics with Quantum Inflation
Wu, Yue-Liang
2015-01-01
In this talk, I present a theory of quantum gravity beyond Einstein. The theory is established based on spinnic and scaling gauge symmetries by treating the gravitational force on the same footing as the electroweak and strong forces. A bi-frame space-time is initiated to describe the laws of nature. One frame space-time is a globally flat coordinate Minkowski space-time that acts as an inertial reference frame for the motions of fields, the other is a locally flat non-coordinate Gravifield space-time that functions as an interaction representation frame for the degrees of freedom of fields. The Gravifield is sided on both the globally flat coordinate space-time and locally flat non-coordinate space-time and characterizes the gravitational force. Instead of the principle of general coordinate invariance in Einstein theory of general relativity, some underlying principles with the postulates of coordinate independence and gauge invariance are motivated to establish the theory of quantum gravity. When transmuti...
Mendes, Raissa F. P.; Ortiz, Néstor
2016-06-01
Scalar-tensor theories of gravity are extensions of general relativity (GR) including an extra, nonminimally coupled scalar degree of freedom. A wide class of these theories, albeit indistinguishable from GR in the weak field regime, predicts a radically different phenomenology for neutron stars, due to a nonperturbative, strong-field effect referred to as spontaneous scalarization. This effect is known to occur in theories where the effective linear coupling β0 between the scalar and matter fields is sufficiently negative, i.e. β0≲-4.35 , and has been strongly constrained by pulsar timing observations. In the test-field approximation, spontaneous scalarization manifests itself as a tachyonic-like instability. Recently, it was argued that, in theories where β0>0 , a similar instability would be triggered by sufficiently compact neutron stars obeying realistic equations of state. In this work we investigate the end state of this instability for some representative coupling functions with β0>0 . This is done both through an energy balance analysis of the existing equilibrium configurations, and by numerically determining the nonlinear Cauchy development of unstable initial data. We find that, contrary to the β00 , which could give rise to novel astrophysical tests of the theory of gravity.
A general theory of linear cosmological perturbations: scalar-tensor and vector-tensor theories
Lagos, Macarena; Ferreira, Pedro G; Noller, Johannes
2016-01-01
We present a method for parametrizing linear cosmological perturbations of theories of gravity, around homogeneous and isotropic backgrounds. The method is sufficiently general and systematic that it can be applied to theories with any degrees of freedom (DoFs) and arbitrary gauge symmetries. In this paper, we focus on scalar-tensor and vector-tensor theories, invariant under linear coordinate transformations. In the case of scalar-tensor theories, we use our framework to recover the simple parametrizations of linearized Horndeski and "Beyond Horndeski" theories, and also find higher-derivative corrections. In the case of vector-tensor theories, we first construct the most general quadratic action for perturbations that leads to second-order equations of motion, which propagates two scalar DoFs. Then we specialize to the case in which the vector field is time-like (\\`a la Einstein-Aether gravity), where the theory only propagates one scalar DoF. As a result, we identify the complete forms of the quadratic act...
Reheating predictions in gravity theories with derivative coupling
Dalianis, Ioannis; Koutsoumbas, George; Ntrekis, Konstantinos; Papantonopoulos, Eleftherios
2017-02-01
We investigate the inflationary predictions of a simple Horndeski theory where the inflaton scalar field has a non-minimal derivative coupling (NMDC) to the Einstein tensor. The NMDC is very motivated for the construction of successful models for inflation, nevertheless its inflationary predictions are not observationally distinct. We show that it is possible to probe the effects of the NMDC on the CMB observables by taking into account both the dynamics of the inflationary slow-roll phase and the subsequent reheating. We perform a comparative study between representative inflationary models with canonical fields minimally coupled to gravity and models with NMDC. We find that the inflation models with dominant NMDC generically predict a higher reheating temperature and a different range for the tilt of the scalar perturbation spectrum ns and scalar-to-tensor ratio r, potentially testable by current and future CMB experiments.
Reheating predictions in Gravity Theories with Derivative Coupling
Dalianis, Ioannis; Ntrekis, Konstantinos; Papantonopoulos, Eleftherios
2016-01-01
We investigate the inflationary predictions of a simple Horndeski theory where the inflaton scalar field has a non-minimal derivative coupling (NMDC) to the Einstein tensor. The NMDC is very motivated for the construction of successful models for inflation, nevertheless its inflationary predictions are not observationally distinct. We show that it is possible to probe the effects of the NMDC on the CMB observables by taking into account both the dynamics of the inflationary slow-roll phase and the subsequent reheating. We perform a comparative study between representative inflationary models with canonical fields minimally coupled to gravity and models with NMDC. We find that the inflation models with dominant NMDC generically predict a higher reheating temperature and a different range for the tilt of the scalar perturbation spectrum $n_s$ and scalar-to-tensor ratio $r$, potentially testable by current and future CMB experiments.
Quintessence interacting dark energy from induced matter theory of gravity
Reyes, L M
2009-01-01
In the context of the induced matter theory of gravity, we investigate the possibility of deriving a 4D quintessential scenario where an interaction between dark energy and dark matter is allowed, and the dark energy component is modeled by a minimally coupled scalar field. Regarding the Ponce de Leon metric, we found that it is possible to obtain such scenario on which the energy densities of dark matter and dark energy, are both depending of the fifth extra coordinate. We obtain that the 4D induced scalar potential for the quintessence scalar field, has the same algebraic form to the one found by Zimdahl and Pavon in the context of usual 4D cosmology.
Noncommutative SO(2,3) gauge theory and noncommutative gravity
Dimitrijevic, Marija
2014-01-01
In this paper noncommutative gravity is constructed as a gauge theory of the noncommutative SO(2,3) group, while the noncommutativity is canonical (constant). The Seiberg-Witten map is used to express noncommutative fields in terms of the corresponding commutative fields. The commutative limit of the model is the Einstein-Hilbert action with the cosmological constant term and the topological Gauss-Bonnet term. We calculate the second order correction to this model and obtain terms that are of zeroth to fourth power in the curvature tensor and torsion. Trying to relate our results with $f(R)$ and $f(T)$ models, we analyze different limits of our model. In the limit of big cosmological constant and vanishing torsion we obtain a $x$-dependent correction to the cosmological constant, i.e. noncommutativity leads to a $x$-dependent cosmological constant. We also discuss the limit of small cosmological constant and vanishing torsion and the teleparallel limit.
A new thermogeomechanical theory for gravity drainage in SAGD
Energy Technology Data Exchange (ETDEWEB)
Cokar, M.; Kallos, M.S.; Gates, I.D. [Dept. of Chemical and Petroleum Engineering, University of Calgary (Canada)
2011-07-01
In the heavy oil and bitumen industry, the steam assisted gravity drainage (SAGD) process is often used to enhance oil recovery. In such deposits, oil usually has no mobility due to its high viscosity and the injection of steam leads to an increase in the mobility of bitumen. Since the thermogeomechanical evolution of the oil sand at the chamber edge is important to the SAGD's performance, this paper aimed at taking these effects into account in a new SAGD drainage formula. The SAGD theory was modified to incorporate the effects of geomechanics and the results were then compared with Butler's model and the Sharma and Gates model. Results showed that thermal expansion has an important impact on oil rates and that geomechanical effects need to be considered when analysing the flow at the edge of steam chambers. This study developed a SAGD drainage formula and demonstrated the importance of geomechanics in the SAGD's performance.
Connecting Through Obstruction; Relating Gauge Gravity and String Theory
Cartwright, Casey
2016-01-01
We consider topological constraints that must be satisfied by formulations of gravitation as a gauge theory. To facilitate the analysis we review and further justify the composite bundle formalism of Tresguerres as a consistent underlying structure capable of incorporating both the local Lorentz and translational degrees of freedom. Identifying an important global structure required by the composite construction, we translate this into conditions on the underlying manifold. We find that in addition to admitting the expected orientability, causality and spin structures, the underlying manifold must also admit a string structure. We take this to imply that even before considerations of quantum consistency, topological considerations of gauge gravity provide a classical motivation for extended degrees of freedom.
Generalized Mattig's relation in Brans-Dicke-Rastall gravity
Salako, Ines G; Jawad, Abdul
2016-01-01
The Geodesic Deviation Equation is being studied in Brans-Dicke-Rastall gravity. We briefly discuss the Brans-Dicke-Rastall gravity and then construct GDE for FLRW metric. In this way, the obtained geodesic deviation equation will correspond to the Brans-Dicke-Rastall gravity. Eventually, we solve numerically the null vector GDE to obtain from Mattig relation, the deviation vector $\\eta(z)$ and observer area distance $r_0(z)$ and compare the results with $\\Lambda$CDM model.
Recent Progress in String Theory and Gravity/Gauge Theory Duality
van Raamsdonk, Mark
2003-05-01
In this talk, I will describe several recent developments in string theory. First, I'll discuss efforts to address the recent observations that the expansion of our universe is accelerating. Using some standard elements of the string theory toolbox (branes, fluxes, and extra dimensions) there has been good progress in constructing string theory models of universes with positive cosmological constant, though these models suggest that this may only be a temporary state of affairs. String theory also provides good reason to study universes with a negative cosmological constant: according to the well-known AdS/CFT conjecture, some of these are equivalent to non-gravitational gauge theories, and this equivalence promises to bring a better understanding both of quantum gravity and of strongly-coupled gauge theories. I will describe an important recent development in this area that permits detailed perturbative calculations on both sides, providing some of the most impressive tests of the correspondence so far.
Semiclassical gravity from the perspective of quantum information theory
Energy Technology Data Exchange (ETDEWEB)
Landulfo, Andre Gustavo Scagliusi [Universidade Federal do ABC (UFABC), Santo Andre, SP (Brazil)
2012-07-01
Full text: Quantum field theory in curved spacetimes makes remarkable predictions about the behavior of quantum fields in the presence of strong gravitational fields. Nevertheless, these striking discoveries raises several issues. The development of a theory at the interface between relativity, quantum mechanics, and information theory could not only shed new light on such questions as well as allowing to uncover new low-energy quantum gravity effects. In this talk I will review several results in this new field. In particular it will be shown that the Bell inequalities can be satisfied rather than violated by quantum mechanics if the detectors making the measurements are set in relativistic motion. It will also be shown that the entanglement between a pair of quits can suffer a sudden death when one of the quits accelerates uniformly for a finite proper time. This result will be used to analyze the behavior of entanglement in the vicinity of a nonrotating chargeless black hole. I will end with a discussion about the prospects of the field, emphasizing the so called 'black hole information paradox' and the question of what is the microscopic origin of the black hole entropy. (author)
Aspects of nonlocality in quantum field theory, quantum gravity and cosmology
Barvinsky, A. O.
2015-02-01
This paper contains a collection of essays on nonlocal phenomena in quantum field theory, gravity and cosmology. Mechanisms of nonlocal contributions to the quantum effective action are discussed within the covariant perturbation expansion in field strengths and spacetime curvatures. Euclidean version of the Schwinger-Keldysh technique for quantum expectation values is presented as a special rule of obtaining the nonlocal effective equations of motion for the mean quantum field from the Euclidean effective action. This rule is applied to a new model of ghost free nonlocal cosmology which can generate the de Sitter (dS) cosmological evolution at an arbitrary value of Λ — a model of dark energy with the dynamical scale selected by a kind of a scaling symmetry breaking mechanism. This model is shown to interpolate between the superhorizon phase of a scalar mediated gravity and the short distance general relativistic limit in a special metric frame related by a nonlocal conformal transformation to the original metric.
Primordial fluctuations from inflation in dRGT bimetric theory of gravity
Energy Technology Data Exchange (ETDEWEB)
Sakakihara, Yuki [Department of Physics, Kyoto University,Kyoto 606-8502 (Japan); Research Center for the Early Universe (RESCEU), Graduate School of Science,The University of Tokyo, Tokyo 113-0033 (Japan); Tanaka, Takahiro [Department of Physics, Kyoto University,Kyoto 606-8502 (Japan); Yukawa Institute for Theoretical Physics, Kyoto University,Kyoto 606-8502 (Japan)
2016-09-19
We investigate primordial gravitational waves and curvature perturbations in de Rham-Gabadadze-Tolley (dRGT) bimetric gravity. We evaluate the power-spectra in the leading order in slow roll. Taking into account the decay of massive graviton, we find that the action up to the second order reduces to the Einstein theory with a non-minimally coupled scalar field, which is simplified to a minimally coupled model by conformal transformation. We also find that the tensor to scalar ratio for large field inflation with power law potential is larger than the general relativity counterpart for any choice of parameters in dRGT bimetric gravity. In addition, we confirm that the usual consistency relation holds and we have a steeper spectrum for gravitational waves.
Computing Black Hole entropy in Loop Quantum Gravity from a Conformal Field Theory perspective
Agullo, Ivan; Diaz-Polo, Jacobo
2009-01-01
Motivated by the analogy proposed by Witten between Chern-Simons and Conformal Field Theories, we explore an alternative way of computing the entropy of a black hole starting from the isolated horizon framework in Loop Quantum Gravity. The consistency of the result opens a window for the interplay between Conformal Field Theory and the description of black holes in Loop Quantum Gravity.
Computing black hole entropy in loop quantum gravity from a conformal field theory perspective
Energy Technology Data Exchange (ETDEWEB)
Agulló, Iván [Enrico Fermi Institute and Department of Physics, University of Chicago, Chicago, IL 60637 (United States); Borja, Enrique F. [Departamento de Física Teórica and IFIC, Centro Mixto Universidad de Valencia-CSIC, Facultad de Física, Universidad de Valencia, Burjassot-46100, Valencia (Spain); Díaz-Polo, Jacobo, E-mail: Ivan.Agullo@uv.es, E-mail: Enrique.Fernandez@uv.es, E-mail: Jacobo.Diaz@uv.es [Institute for Gravitation and the Cosmos, Physics Department, Penn State, University Park, PA 16802 (United States)
2009-07-01
Motivated by the analogy proposed by Witten between Chern-Simons and conformal field theories, we explore an alternative way of computing the entropy of a black hole starting from the isolated horizon framework in loop quantum gravity. The consistency of the result opens a window for the interplay between conformal field theory and the description of black holes in loop quantum gravity.
Hořava Gravity in the Effective Field Theory formalism: From cosmology to observational constraints
Frusciante, Noemi; Raveri, Marco; Vernieri, Daniele; Hu, Bin; Silvestri, Alessandra
2016-09-01
We consider Hořava gravity within the framework of the effective field theory (EFT) of dark energy and modified gravity. We work out a complete mapping of the theory into the EFT language for an action including all the operators which are relevant for linear perturbations with up to sixth order spatial derivatives. We then employ an updated version of the EFTCAMB/EFTCosmoMC package to study the cosmology of the low-energy limit of Hořava gravity and place constraints on its parameters using several cosmological data sets. In particular we use cosmic microwave background (CMB) temperature-temperature and lensing power spectra by Planck 2013, WMAP low- ℓ polarization spectra, WiggleZ galaxy power spectrum, local Hubble measurements, Supernovae data from SNLS, SDSS and HST and the baryon acoustic oscillations measurements from BOSS, SDSS and 6dFGS. We get improved upper bounds, with respect to those from Big Bang Nucleosynthesis, on the deviation of the cosmological gravitational constant from the local Newtonian one. At the level of the background phenomenology, we find a relevant rescaling of the Hubble rate at all epoch, which has a strong impact on the cosmological observables; at the level of perturbations, we discuss in details all the relevant effects on the observables and find that in general the quasi-static approximation is not safe to describe the evolution of perturbations. Overall we find that the effects of the modifications induced by the low-energy Hořava gravity action are quite dramatic and current data place tight bounds on the theory parameters.
Galileons Coupled to Massive Gravity: General Analysis and Cosmological Solutions
Goon, Garrett; Hinterbichler, Kurt; Mukohyama, Shinji; Trodden, Mark
2014-01-01
We further develop the framework for coupling galileons and Dirac-Born-Infeld (DBI) scalar fields to a massive graviton while retaining both the non-linear symmetries of the scalars and ghost-freedom of the theory. The general construction is recast in terms of vielbeins which simplifies calculations and allows for compact expressions. Expressions for the general form of the action are derived, with special emphasis on those models which descend from maximally symmetric spaces. We demonstrate the existence of maximally symmetric solutions to the fully non-linear theory and analyze their spectrum of quadratic fluctuations. Finally, we consider self-accelerating cosmological solutions and study their perturbations, showing that the vector and scalar modes have vanishing kinetic terms.
Cosmology in beyond-generalized Proca theories
Nakamura, Shintaro; Kase, Ryotaro; Tsujikawa, Shinji
2017-05-01
The beyond-generalized Proca theories are the extension of second-order massive vector-tensor theories (dubbed generalized Proca theories) with two transverse vector modes and one longitudinal scalar besides two tensor polarizations. Even with this extension, the propagating degrees of freedom remain unchanged on the isotropic cosmological background without an Ostrogradski instability. We study the cosmology in beyond-generalized Proca theories by paying particular attention to the dynamics of late-time cosmic acceleration and resulting observational consequences. We derive conditions for avoiding ghosts and instabilities of tensor, vector, and scalar perturbations and discuss viable parameter spaces in concrete models allowing the dark energy equation of state smaller than -1 . The propagation speeds of those perturbations are subject to modifications beyond the domain of generalized Proca theories. There is a mixing between scalar and matter sound speeds, but such a mixing is suppressed during most of the cosmic expansion history without causing a new instability. On the other hand, we find that derivative interactions arising in beyond-generalized Proca theories give rise to important modifications to the cosmic growth history. The growth rate of matter perturbations can be compatible with the redshift-space distortion data due to the realization of gravitational interaction weaker than that in generalized Proca theories. Thus, it is possible to distinguish the dark energy model in beyond-generalized Proca theories from the counterpart in generalized Proca theories as well as from the Λ CDM model.
de la Cruz-Dombriz, Álvaro; Luongo, Orlando; Reverberi, Lorenzo
2016-01-01
The onset of dark energy domination depends on the particular gravitational theory driving the cosmic evolution. Model independent techniques are crucial to test both the present $\\Lambda$CDM cosmological paradigm and alternative theories, making the least possible number of assumptions about the Universe. In this paper we investigate whether cosmography is able to distinguish between different gravitational theories, by determining bounds on model parameters for three different extensions of General Relativity, i.e. $k-$essence, $F(T)$ and $f(R)$ theories. We expand each class of theories in powers of redshift $z$ around the present time, making no additional assumptions. This procedure is an extension of previous work and can be seen as the most general approach for testing extended theories of gravity with cosmography. In the case of $F(T)$ and $f(R)$ theories, we show that some assumptions on model parameters often made in previous works are superfluous or unjustified. We use data from the Union2.1 SN cat...
On the stability conditions for theories of modified gravity coupled to matter fields
De Felice, Antonio; Papadomanolakis, Georgios
2016-01-01
We present a thorough stability analysis of modified gravity theories when the coupling to matter fields is considered. We use the Effective Field Theory framework for Dark Energy and Modified Gravity to retain a general approach for the gravity sector and a Sorkin-Schutz action for the matter one. Then, we work out the proper viability conditions to guarantee in the scalar sector the absence of ghosts, gradient and tachyonic instabilities. The absence of ghosts can be achieved by demanding a positive kinetic matrix, while the lack of a gradient instability is ensured by imposing a positive speed of propagation for all the scalar modes. In case of tachyonic instability, the mass eigenvalues have been studied and we work out the appropriate expressions. For the latter, an instability occurs only when the negative mass eigenvalue is much larger, in absolute value, than the Hubble parameter. We discuss the results for the minimally coupled quintessence model showing for a particular set of parameters two typical...
Spherically symmetric vacuum in covariant F (T )=T +α/2 T2+O (Tγ) gravity theory
DeBenedictis, Andrew; Ilijić, Saša
2016-12-01
Recently, a fully covariant version of the theory of F (T ) torsion gravity has been introduced by M. Kršśák and E. Saridakis [Classical Quantum Gravity 33, 115009 (2016)]. In covariant F (T ) gravity, the Schwarzschild solution is not a vacuum solution for F (T )≠T , and therefore determining the spherically symmetric vacuum is an important open problem. Within the covariant framework, we perturbatively solve the spherically symmetric vacuum gravitational equations around the Schwarzschild solution for the scenario with F (T )=T +(α /2 )T2 , representing the dominant terms in theories governed by Lagrangians analytic in the torsion scalar. From this, we compute the perihelion shift correction to solar system planetary orbits as well as perturbative gravitational effects near neutron stars. This allows us to set an upper bound on the magnitude of the coupling constant, α , which governs deviations from general relativity. We find the bound on this nonlinear torsion coupling constant by specifically considering the uncertainty in the perihelion shift of Mercury. We also analyze a bound from a similar comparison with the periastron orbit of the binary pulsar PSR J0045-7319 as an independent check for consistency. Setting bounds on the dominant nonlinear coupling is important in determining if other effects in the Solar System or greater universe could be attributable to nonlinear torsion.
Generalized BRST Symmetry and Gaugeon Formalism for Perturbative Quantum Gravity: Novel Observation
Upadhyay, Sudhaker
2014-01-01
In this paper the novel features of Yokoyama gaugeon formalism are stressed out for the theory of perturbative quantum gravity in Einstein curved spacetime. The quantum gauge transformations for the theory of perturbative gravity are demonstrated in the framework of gaugeon formalism. These quantum gauge transformations lead to renormalized gauge parameter. Further, we analyse the BRST symmetric gaugeon formalism which embeds more acceptable Kugo-Ojima subsidiary condition. Further, the BRST symmetry is made finite and field-dependent. Remarkably, the Jacobian of path integral under finite and field-dependent BRST symmetry amounts to the exact gaugeon action in the effective theory of perturbative quantum gravity.
Brans-Dicke theory of gravity with torsion: A possible solution of $\\omega$-problem
Wu, Yu-Huei
2012-01-01
We study Brans-Dicke theory of gravity in Riemann-Cartan space-times, and obtain general torsion solutions, which are completely determined by Brans-Dicke scalar field $\\Phi$, in the false vacuum energy dominated epoch. The substitution of the torsion solutions back to our action gives the original Brans-Dicke action with $\\Phi$-dependent Brans-Dicke parameter $\\omega(\\Phi)$. The evolution of $\\omega(\\Phi)$ during inflation is studied and it yields that $\\omega$ approaches to infinity at the end of inflation. It may solve the $\\omega$-problem in the extended inflation model.
Gravitational Waves and Inspiraling Compact Binaries in Alternative Theories of Gravity
Mirshekari, Saeed
2013-01-01
This dissertation consists of four parts. In Part I, we briefly review fundamental theories of gravity, performed experimental tests, and gravitational waves. The framework and the methods that we use in our calculations are discussed in Part II. This part includes reviewing the methods of the Parametrized Post-Newtonian (PPN) framework, Direct Integration of Relaxed Einstein Equations (DIRE), and Matched Filtering. In Part III, we calculate the explicit equations of motion for non-spinning compact objects (neutron stars or black holes) to 2.5 post-Newtonian order, or $O(v/c)^5$ beyond Newtonian gravity, in a general class of alternative theories to general relativity known as scalar-tensor theories. For the conservative part of the motion, we obtain the two-body Lagrangian and conserved energy and momentum through second post-Newtonian order. We find the contributions to gravitational radiation reaction to 1.5 post-Newtonian and 2.5 post-Newtonian orders, the former corresponding to the effects of dipole gra...
How Zwicky already ruled out modified gravity theories without dark matter
Nieuwenhuizen, Theodorus Maria
2016-01-01
Various theories, such as MOND, MOG, Emergent Gravity and $f(R)$ theories avoid dark matter by assuming a change in General Relativity and/or in Newton's law. Galactic rotation curves are typically described well. Here the application to galaxy clusters is considered, focussed on the good lensing and X-ray data for A1689. As a start, the no-dark-matter case is confirmed to work badly: the need for dark matter starts near the cluster centre, where Newton's law is still supposed to be valid. This leads to the conundrum discovered by Zwicky, which is likely only solvable if the theories assume additional (dark) matter. Neutrinos with eV masses serve well without altering the successes in (dwarf) galaxies.
General Systems Theory and Instructional Design.
Salisbury, David F.
The use of general systems theory in the field of instructional systems design (ISD) is explored in this paper. Drawing on work by Young, the writings of 12 representative ISD writers and researchers were surveyed to determine the use of 60 general systems theory concepts by the individual authors. The average number of concepts used by these…
Singular Hypersurfaces in Scalar-Tensor Theories of Gravity
Barrabès, C
1997-01-01
We study singular hypersurfaces in tensor multi-scalar theories of grav= ity. We derive in a distributional and then in an intrinsic way, the general equations of junction valid for all types of hypersurfaces, in particular= for lightlike shells and write the general equations of evolution for these objects. We apply this formalism to various examples in static sphericall= y symmetric spacetimes, and to the study of planar domain walls and plane impulsive waves.
Manifestly Gauge Invariant Perturbations of Scalar-Tensor Theories of Gravity
Han, Yu; Ma, Yongge
2015-01-01
The general relativistic perturbations of scalar-tensor theories (STT) of gravity are studied in a manifestly gauge invariant Hamiltonian formalism. After the derivation of the Hamiltonian equations of motion in this framework, the gauge invariant formalism is used to compute the evolution equations of linear perturbations around a general relativistic spacetime background in the Jordan frame. These equations are then specialized to the case of a flat FRW cosmological background. Furthermore, the equivalence between the Jordan frame and the Einstein frame of STT in the manifestly gauge invariant Hamiltonian formalism is analyzed, and it is shown that also in this framework they can be related by a conformal transformation. Finally, the obtained evolution equations for the linear perturbations in our formalism are compared with those in the standard cosmological perturbation theory. It turns out that the perturbation equations in the two different formalisms coincide with each other in a suitable limit.
Axion-dilaton-modulus gravity theory of Brans-Dicke-type and conformal symmetry
Quirós, I
2000-01-01
Conformal symmetry is investigated within the context of axion-dilaton-modulus theory of gravity of Brans-Dicke-type. A distinction is made between general conformal symmetry and invariance under transformations of the physical units. The conformal degree of symmetry of the theory is studied when quantum fermion (lepton) modes with electromagnetic interaction are considered. Based on the requirement of invariance of the physical laws under general transformations of the units of measure, arguments are given that point at a matter action with non-minimal coupling of the dilaton to the matter fields as the most viable description of the world within the context of the model studied. The geometrical implications of the results obtained are discussed.
Cosmological Observations in a Modified Theory of Gravity (MOG
Directory of Open Access Journals (Sweden)
John. W. Moffat
2013-06-01
Full Text Available Our Modified Gravity Theory (MOG is a gravitational theory without exotic dark matter, based on an action principle. MOG has been used successfully tomodel astrophysical phenomena, such as galaxy rotation curves, galaxy cluster masses and lensing. MOG may also be able to account for cosmological observations. We assume that the MOG point source solution can be used to describe extended distributions of matter via an appropriately modified Poisson equation. We use this result to model perturbation growth in MOG and find that it agrees well with the observed matter power spectrum at present. As the resolution of the power spectrum improves with increasing survey size, however, significant differences emerge between the predictions of MOG and the standard Λ-cold dark matter (Λ-CDM model, as in the absence of exotic darkmatter, oscillations of the power spectrum in MOG are not suppressed. We can also use MOG to model the acoustic power spectrum of the cosmic microwave background. A suitably adapted semi-analytical model offers a first indication that MOG may pass this test and correctly model the peak of the acoustic spectrum.
Generalized second law of thermodynamics in f(T) gravity
Energy Technology Data Exchange (ETDEWEB)
Karami, K.; Abdolmaleki, A., E-mail: KKarami@uok.ac.ir, E-mail: AAbdolmaleki@uok.ac.ir [Department of Physics, University of Kurdistan, Pasdaran St., Sanandaj (Iran, Islamic Republic of)
2012-04-01
We investigate the validity of the generalized second law (GSL) of gravitational thermodynamics in the framework of f(T) modified teleparallel gravity. We consider a spatially flat FRW universe containing only the pressureless matter. The boundary of the universe is assumed to be enclosed by the Hubble horizon. For two viable f(T) models containing f(T) = T+μ{sub 1}((−T)){sup n} and f(T) = T−μ{sub 2}T(1−e{sup βT{sub 0}/T}), we first calculate the effective equation of state and deceleration parameters. Then, (we investigate the null and strong energy conditions and conclude that a sudden future singularity appears in both models. Furthermore, using a cosmographic analysis we check the viability of two models. Finally, we examine the validity of the GSL and find that for both models it) is satisfied from the early times to the present epoch. But in the future, the GSL is violated for the special ranges of the torsion scalar T.
Kaluza's theory in generalized coordinates
García-Perciante, A L; García-Colin, L S; Garcia-Perciante, Ana Laura; Sandoval-Villalbazo, Alfredo
2001-01-01
Maxwell's equations can be obtained in generalized coordinates by considering the electromagnetic field as an external agent. The work here presented shows how to obtain the electrodynamics for a charged particle in generalized coordinates eliminating the concept of external force. Based on Kaluza's formalism, the one here presented extends the 5x5 metric into a 6x6 space-time giving enough room to include magnetic monopoles in a very natural way.
A Contextualised General Systems Theory
Kirsty Kitto
2014-01-01
A system is something that can be separated from its surrounds, but this definition leaves much scope for refinement. Starting with the notion of measurement, we explore increasingly contextual system behaviour and identify three major forms of contextuality that might be exhibited by a system: (1) between components; (2) between system and experimental method; and (3) between a system and its environment. Quantum theory is shown to provide a highly useful formalism from which all three forms...
Energy in class of scalar-tensor theories of gravity
Energy Technology Data Exchange (ETDEWEB)
Barraco, D.; Hamity, V. (Universidad Nacional de Cordoba, Cordoba (Antigua and Barbuda)); Calvo, A.; Seco, J. (Departamento de Fisica General de la Atmosfera, Universidad de Salamanca, Salamanca (Spain))
1994-01-01
We investigate the equality of inertial and gravitational mass in a wide class of scalar tensor theories. We derive a general expression for the active mass (gravitational mass) and the inertial mass related by a term which can be seen as the energy of the scalar field. (Author) 13 refs.
Constraining theories of gravity from Light Deviation Experiments
Bustos, Richard; Biswas, Tirthabir; Carl Brans Collaboration, Dr.; Tirthabir Biswas Collaboration, Dr.
2016-03-01
Modifications of Einstein's theory of General Relativity (GR) are notorious for introducing ghosts and tachyons which renders these theories classically unstable and any attempts to quantize them doomed to fail. Over the last few years, concrete criteria on covariant modifications to GR have been derived that ensures that the gravitational theory is free from such instabilities, at least, around the Minkowski vacuum. The most general consistent action can be parameterized by two mass scales: the first one controls the scale of nonlocality in the graviton interaction, and the second characterizes the mass of a Brans-Dicke type scalar mode that can be present in the metric tensor. Our goal has been to develop techniques to directly constrain these mass parameters from experimental tests of GR. In particular, I will talk about the constraints from the light bending experiments. Support from the SURE Grant and Dr. Brans.
Hehl, Friedrich W; Puetzfeld, Dirk
2013-01-01
Ever since E.Cartan in the 1920s enriched the geometric framework of general relativity (GR) by introducing a {\\it torsion} of spacetime, the question arose whether one could find a measurement technique for detecting the presence of a torsion field. Mao et al.(2007) claimed that the rotating quartz balls in the gyroscopes of the Gravity Probe B experiment, falling freely on an orbit around the Earth, should "feel" the torsion. Similarly, March et al.(2011) argue with the precession of the Moon and the Mercury and extend later their considerations to the Lageos satellite.--- A consistent theory of gravity with torsion emerged during the early 1960's as gauge theory of the Poincar\\'e group. This Poincar\\'e gauge theory of gravity incorporates as simplest viable cases the Einstein-Cartan(-Sciama-Kibble) theory (EC), the teleparallel equivalent GR|| of GR, and GR itself. So far, PG and, in particular, the existence of torsion have {\\it not} been experimentally confirmed. However, PG is to be considered as the st...
Can dark matter be an artifact of extended theories of gravity?
Energy Technology Data Exchange (ETDEWEB)
Choudhury, Sayantan; Sen, Manibrata [Tata Institute of Fundamental Research, Department of Theoretical Physics, Mumbai (India); Sadhukhan, Soumya [Institute of Mathematical Sciences, C.I.T Campus, Chennai (India)
2016-09-15
In this article, we propose different background models of extended theories of gravity, which are minimally coupled to the SM fields, to explain the possibility of genesis of dark matter without affecting the SM particle sector. We modify the gravity sector by allowing quantum corrections motivated from (1) local f(R) gravity and (2) non-minimally coupled gravity with SM sector and dilaton field. Next we apply a conformal transformation on the metric to transform the action back to the Einstein frame. We also show that an effective theory constructed from these extended theories of gravity and SM sector looks exactly the same. Using the relic constraint observed by Planck 2015, we constrain the scale of the effective field theory (Λ{sub UV}) as well as the dark matter mass (M). We consider two cases: (1) light dark matter (LDM) and (2) heavy dark matter (HDM), and we deduce upper bounds on thermally averaged cross section of dark matter annihilating to SM particles. Further we show that our model naturally incorporates self-interactions of dark matter. Using these self-interactions, we derive the constraints on the parameters of (1) local f(R) gravity and (2) non-minimally coupled gravity from a dark matter self-interaction. Finally, we propose some different UV complete models from a particle physics point of view, which can give rise to the same effective theory that we have deduced from extended theories of gravity. (orig.)
Can dark matter be an artifact of extended theories of gravity?
Choudhury, Sayantan; Sen, Manibrata; Sadhukhan, Soumya
2016-09-01
In this article, we propose different background models of extended theories of gravity, which are minimally coupled to the SM fields, to explain the possibility of genesis of dark matter without affecting the SM particle sector. We modify the gravity sector by allowing quantum corrections motivated from (1) local f( R) gravity and (2) non-minimally coupled gravity with SM sector and dilaton field. Next we apply a conformal transformation on the metric to transform the action back to the Einstein frame. We also show that an effective theory constructed from these extended theories of gravity and SM sector looks exactly the same. Using the relic constraint observed by Planck 2015, we constrain the scale of the effective field theory (Λ _{UV}) as well as the dark matter mass ( M). We consider two cases: (1) light dark matter (LDM) and (2) heavy dark matter (HDM), and we deduce upper bounds on thermally averaged cross section of dark matter annihilating to SM particles. Further we show that our model naturally incorporates self-interactions of dark matter. Using these self-interactions, we derive the constraints on the parameters of (1) local f( R) gravity and (2) non-minimally coupled gravity from a dark matter self-interaction. Finally, we propose some different UV complete models from a particle physics point of view, which can give rise to the same effective theory that we have deduced from extended theories of gravity.
Nam, Soonkeon
2016-01-01
We apply the Wald formalism to obtain masses and angular momenta of black holes in three dimensional gravity theories using first order formalism. Wald formalism suggests mass and angular momentum of black hole as an integration of some charge variation form at its boundary. The action of the three dimensional gravity theories can be represented by the form including some auxiliary fields. As well-known examples we have calculated mass and angular momentum of some black holes in topologically massive gravity and new massive gravity theories using first order formalism. We have also calculated mass and angular momentum of BTZ black hole and new type black hole in minimal massive gravity theory with the action represented by first order formalism.
3-Space In-Flow Theory of Gravity: Boreholes, Blackholes and the Fine Structure Constant
Cahill, R T
2006-01-01
A theory of 3-space explains the phenomenon of gravity as arising from the time-dependence and inhomogeneity of the differential flow of this 3-space. The emergent theory of gravity has two gravitational constants: G - Newton's constant, and a dimensionless constant - alpha. Various experiments and astronomical observations have shown that alpha is the fine structure constant 1/137. Here we analyse the Greenland Ice Shelf and Nevada Test Site borehole g anomalies, and confirm with increased precision this value of alpha. This and other successful tests of this theory of gravity, including the supermassive black holes in globular clusters and galaxies, and the `dark-matter' effect in spiral galaxies, demonstrates the validity of this theory of gravity. This success implies that Newtonian gravity was fundamentally flawed from the beginning.
Energy distributions of Bianchi type-VI h Universe in general relativity and teleparallel gravity
Özkurt, Şeref; Aygün, Sezg&idot; n.
2017-04-01
In this paper, we have investigated the energy and momentum density distributions for the inhomogeneous generalizations of homogeneous Bianchi type-VI h metric with Einstein, Bergmann-Thomson, Landau-Lifshitz, Papapetrou, Tolman and Møller prescriptions in general relativity (GR) and teleparallel gravity (TG). We have found exactly the same results for Einstein, Bergmann-Thomson and Landau-Lifshitz energy-momentum distributions in Bianchi type-VI h metric for different gravitation theories. The energy-momentum distributions of the Bianchi type- VI h metric are found to be zero for h = -1 in GR and TG. However, our results agree with Tripathy et al, Tryon, Rosen and Aygün et al.
Indian Academy of Sciences (India)
SEREF ÖZKURT; SEZGIN AYGÜN
2017-04-01
In this paper, we have investigated the energy and momentum density distributions for the inhomogeneous generalizations of homogeneous Bianchi type-$VI_{h}$ metric with Einstein, Bergmann–Thomson, Landau–Lifshitz,Papapetrou, Tolman and M$\\phi$ller prescriptions in general relativity (GR) and teleparallel gravity (TG). We have found exactly the same results for Einstein, Bergmann–Thomson and Landau–Lifshitz energy–momentum distributions in Bianchi type-$VI_{h}$ metric for different gravitation theories. The energy–momentum distributions of the Bianchi type-$VI_{h}$ metric are found to be zero for $h$ = −1 in GR and TG. However, our results agree with Tripathy et al, Tryon, Rosen and Aygün et al.
Generalisation for regular black holes on general relativity to f(R) gravity
Energy Technology Data Exchange (ETDEWEB)
Rodrigues, Manuel E. [Universidade Federal do Para Campus Universitario de Abaetetuba, Faculdade de Ciencias Exatas e Tecnologia, Abaetetuba, Para (Brazil); Universidade Federal do Para, Faculdade de Fisica, PPGF, Belem, Para (Brazil); Fabris, Julio C. [Universidade Federal do Espirito Santo, Vitoria, ES (Brazil); National Research Nuclear University MEPhI, Moscow (Russian Federation); Junior, Ednaldo L.B. [Universidade Federal do Para, Faculdade de Fisica, PPGF, Belem, Para (Brazil); Universidade Federal do Para, Campus Universitario de Tucurui, Faculdade de Engenharia da Computacao, Tucurui, Para (Brazil); Marques, Glauber T. [Universidade Federal Rural da Amazonia ICIBE - LASIC, Belem, PA (Brazil)
2016-05-15
IIn this paper, we determine regular black hole solutions using a very general f(R) theory, coupled to a nonlinear electromagnetic field given by a Lagrangian L{sub NED}. The functions f(R) and L{sub NED} are in principle left unspecified. Instead, the model is constructed through a choice of the mass function M(r) presented in the metric coefficients. Solutions which have a regular behaviour of the geometric invariants are found. These solutions have two horizons, the event horizon and the Cauchy horizon. All energy conditions are satisfied in the whole space-time, except the strong energy condition (SEC), which is violated near the Cauchy horizon.We present also a new theorem related to the energy conditions in f(R) gravity, re-obtaining the well-known conditions in the context of general relativity when the geometry of the solution is the same. (orig.)
A general theory of rotorcraft trim
Directory of Open Access Journals (Sweden)
David A. Peters
1996-01-01
Full Text Available In this paper we offer a general theory of rotorcraft trim. The theory is set in the context of control theory. It allows for completely arbitrary trim controls and trim settings for multi-rotor aircraft with tests to ensure that a system is trimmable. In addition, the theory allows for “optimal trim” in which some variable is minimized or maximized rather than set to a specified value. The theory shows that sequential trim cannot work for free flight. The theory is not tied to any particular trim algorithm; but, in this paper, it is exercised with periodic shooting to show how free-flying rotorcraft can be trimmed in a variety of ways (zero yaw, zero pitch, zero roll, minimum power, etc. by use of the general theory. The paper also discusses applications to harmonic balance and auto-pilot trim techniques.
Directory of Open Access Journals (Sweden)
Rami Ahmad El-Nabulsi
2015-08-01
Full Text Available Recently, non-standard Lagrangians have gained a growing importance in theoretical physics and in the theory of non-linear differential equations. However, their formulations and implications in general relativity are still in their infancies despite some advances in contemporary cosmology. The main aim of this paper is to fill the gap. Though non-standard Lagrangians may be defined by a multitude form, in this paper, we considered the exponential type. One basic feature of exponential non-standard Lagrangians concerns the modified Euler-Lagrange equation obtained from the standard variational analysis. Accordingly, when applied to spacetime geometries, one unsurprisingly expects modified geodesic equations. However, when taking into account the time-like paths parameterization constraint, remarkably, it was observed that mutually discrete gravity and discrete spacetime emerge in the theory. Two different independent cases were obtained: A geometrical manifold with new spacetime coordinates augmented by a metric signature change and a geometrical manifold characterized by a discretized spacetime metric. Both cases give raise to Einstein’s field equations yet the gravity is discretized and originated from “spacetime discreteness”. A number of mathematical and physical implications of these results were discussed though this paper and perspectives are given accordingly.
Peng, Jun-Jin
2016-01-01
In this paper, we investigate the conserved charges of generally diffeomorphism invariant gravity theories with a wide variety of matter fields, particularly of the theories with multiple scalar fields and $p$-form potentials, in the context of the off-shell generalized Abbott-Deser-Tekin (ADT) formalism. We first construct a new off-shell ADT current that consists of the terms for the variation of a Killing vector and expressions of the field equations as well as the Lie derivative of a surface term with respect to the Killing vector within the framework of generally diffeomorphism invariant gravity theories involving various matter fields. After deriving the off-shell ADT potential corresponding to this current, we propose a formula of conserved charges for these theories due to the potential. Next, we derive the off-shell ADT potential associated with the generic Lagrangian that describes a large range of gravity theories with a number of scalar fields and $p$-form potentials. Finally, the properties of th...
Blasi, Alberto; Maggiore, Nicola
2017-01-01
In this paper we consider the issue of massive gravity from a pure field theoretical point of view, as the massive deformation of the gauge theory for a symmetric rank-2 tensor field. We look for the most general massive theory with well defined propagators, imposing the absence of unphysical poles. We find several possibilities, depending on the choice of the gauge fixing term. Amongst these, two solutions with good massless limit are found. The request of the absence of tachyons, alone, does not isolate the Fierz-Pauli case: several examples of massive theories, which may or may not include the Fierz-Pauli mass term, are given. On the other hand, the Fierz-Pauli theory can be uniquely identified by means of a symmetry: it turns out the the Fierz-Pauli massive gravity is the only element of the cohomology of a BRS operator.
Generalizing Boolean Satisfiability II: Theory
Dixon, H E; Luks, E M; Parkes, A J; 10.1613/jair.1555
2011-01-01
This is the second of three planned papers describing ZAP, a satisfiability engine that substantially generalizes existing tools while retaining the performance characteristics of modern high performance solvers. The fundamental idea underlying ZAP is that many problems passed to such engines contain rich internal structure that is obscured by the Boolean representation used; our goal is to define a representation in which this structure is apparent and can easily be exploited to improve computational performance. This paper presents the theoretical basis for the ideas underlying ZAP, arguing that existing ideas in this area exploit a single, recurring structure in that multiple database axioms can be obtained by operating on a single axiom using a subgroup of the group of permutations on the literals in the problem. We argue that the group structure precisely captures the general structure at which earlier approaches hinted, and give numerous examples of its use. We go on to extend the Davis-Putnam-Logemann-...
On Holographic R\\'enyi Entropy in Some Modified Theories of Gravity
Dey, Anshuman; Sarkar, Tapobrata
2016-01-01
We perform a detailed analysis of holographic entanglement R\\'enyi entropy in some modified theories of gravity with four dimensional conformal field theory duals. First, we construct perturbative black hole solutions in a recently proposed model of Einsteinian cubic gravity in five dimensions, and compute the R\\'enyi entropy as well as the scaling dimension of the twist operators in the dual field theory. Consistency of these results are verified from the AdS/CFT correspondence, via a corresponding computation of the Weyl anomaly on the gravity side. Similar analyses are then carried out for three other examples of modified gravity in five dimensions that include a chemical potential, namely Born-Infeld gravity, charged quasi-topological gravity and a class of Weyl corrected gravity theories with a gauge field, with the last example being treated perturbatively. Some interesting bounds in the dual conformal field theory parameters in quasi-topological gravity are pointed out. We also provide arguments on the...
Risk analysis of gravity dam instability using credibility theory Monte Carlo simulation model
Xin, Cao; Chongshi, Gu
2016-01-01
Risk analysis of gravity dam stability involves complicated uncertainty in many design parameters and measured data. Stability failure risk ratio described jointly by probability and possibility has deficiency in characterization of influence of fuzzy factors and representation of the likelihood of risk occurrence in practical engineering. In this article, credibility theory is applied into stability failure risk analysis of gravity dam. Stability of gravity dam is viewed as a hybrid event co...
Cosmic Censorship in Lorentz Violating Theories of Gravity
Meiers, Michael; Afshordi, Niayesh
2015-01-01
Is Cosmic Censorship special to General Relativity, or can it survive a violation of equivalence principle? Recent studies have shown that singularities in Lorentz violating Einstein-Aether (or Horava-Lifhsitz) theories can lie behind a universal horizon in simple black hole spacetimes. Even infinitely fast signals cannot escape these universal horizons. We extend this result, for an incompressible aether, to 3+1d dynamical or spinning spacetimes which possess inner killing horizons, and show that a universal horizon always forms in between the outer and (would-be) inner horizons. This finding suggests a notion of Cosmic Censorship, given that geometry in these theories never evolves beyond the universal horizon (avoiding potentially singular inner killing horizons). A surprising result is that there are 3 distinct possible stationary universal horizons for a spinning black hole, only one of which matches the dynamical spherical solution. This motivates dynamical studies of collapse in Einstein-Aether theorie...
Effective Gravitational Wave Stress-energy Tensor in Alternative Theories of Gravity
Stein, Leo C; Hughes, Scott A
2010-01-01
The inspiral of binary systems in vacuum is controlled by the rate of change of the system's energy, angular momentum and Carter constant. In alternative theories, such a change is induced by the effective stress-energy carried away by gravitational radiation and any other propagating degrees of freedom. We employ perturbation theory and the short-wavelength approximation to compute this stress-energy tensor in a wide class of alternative theories. We find that this tensor is generally a modification of that first computed by Isaacson, where the corrections can dominate over the general relativistic term. In a wide class of theories, however, these corrections identically vanish at asymptotically flat, future, null infinity, reducing the stress-energy tensor to Isaacson's. We exemplify this phenomenon by first considering dynamical Chern-Simons modified gravity, which corrects the action via a scalar field and the contraction of the Riemann tensor and its dual. We then consider a wide class of theories with d...
Dengiz, Suat
2014-01-01
Weyl-invariant extensions of three-dimensional New Massive Gravity, generic n-dimensional Quadratic Curvature Gravity theories and three-dimensional Born-Infeld gravity theory are analyzed in details. As required by Weyl-invariance, the actions of these gauge theories do not contain any dimensionful parameter hence the local symmetry is spontaneously broken in (Anti) de Sitter vacua in complete analogy with the Standard Model Higgs mechanism. In flat vacuum, symmetry breaking mechanism is more complicated: The dimensionful parameters come from dimensional transmutation in the quantum field theory; therefore, the conformal symmetry is radiatively broken (at two loop level in 3-dimensions and at one-loop level in 4-dimensions) \\`{a} la Coleman-Weinberg mechanism. In the broken phases, save for New Massive Gravity, the theories generically propagate with a unitary (tachyon and ghost-free) massless tensor, massive (or massless) vector and massless scalar particles for the particular intervals of the dimensionless...
Camci, U; Oz, I Basaran
2016-01-01
The Noether symmetry approach is useful tool to restrict the arbitrariness in a gravity theory when the equations of motion are underdetermined due to the high number of functions to be determined in the ansatz. We consider two scalar-coupled theories of gravity, one motivated by induced gravity, the other more standard; in Bianchi I, Bianchi III and Kantowski-Sachs cosmological models. For these models, we present a full set of Noether gauge symmetries, which are more general than those obtained by the strict Noether symmetry approach in our recent work. Some exact solutions are derived using the first integrals corresponding to the obtained Noether gauge symmetries.
Teaching Evolutionary Theory as General Education.
Todd, Paul
1984-01-01
Provides a rationale for including evolution as part of a college general education curriculum, discussing the content of evolutionary theory, instructional principles, Darwin's contributions, evolution and religion, and the relationship of evolution with current events. (DMM)
A Covariant Master Theory for Novel Galilean Invariant Models and Massive Gravity
Gabadadze, Gregory; Khoury, Justin; Pirtskhalava, David; Trodden, Mark
2012-01-01
Coupling the galileons to a curved background has been a tradeoff between maintaining second order equations of motion, maintaining the galilean shift symmetries, and allowing the background metric to be dynamical. We propose a construction which can achieve all three for a novel class of galilean invariant models, by coupling a scalar with the galilean symmetry to a massive graviton. This generalizes the brane construction for galileons, by adding to the brane a dynamical metric, (non-universally) interacting with the galileon field. Alternatively, it can be thought of as an extension of the ghost-free massive gravity, or as a massive graviton-galileon scalar-tensor theory. In the decoupling limit of these theories, new kinds of galileon invariant interactions arise between the scalar and the longitudinal mode of the graviton. These have higher order equations of motion and infinite powers of the field, yet are ghost-free.
How Zwicky already ruled out modified gravity theories without dark matter
Energy Technology Data Exchange (ETDEWEB)
Nieuwenhuizen, Theodorus Maria [Institute for Theoretical Physics, University of Amsterdam (Netherlands); International Institute of Physics, UFRG, Natal (Brazil)
2017-06-15
Various theories, such as MOND, MOG, Emergent Gravity and f(R) theories avoid dark matter by assuming a change in General Relativity and/or in Newton's law. Galactic rotation curves are typically described well. Here the application to galaxy clusters is considered, focussed on the good lensing and X-ray data for A1689. As a start, the no-dark-matter case is confirmed to work badly: the need for dark matter starts near the cluster centre, where Newton's law is still supposed to be valid. This leads to the conundrum discovered by Zwicky, which is likely only solvable in his way, namely by assuming additional (dark) matter. Neutrinos with eV masses serve well without altering the successes in (dwarf) galaxies. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Numerical simulations of stellar collapse in scalar-tensor theories of gravity
Gerosa, Davide; Ott, Christian D
2016-01-01
We present numerical-relativity simulations of spherically symmetric core collapse and compact-object formation in scalar-tensor theories of gravity. The additional scalar degree of freedom introduces a propagating monopole gravitational-wave mode. Detection of monopole scalar waves with current and future gravitational-wave experiments may constitute smoking gun evidence for strong-field modifications of General Relativity. We collapse both polytropic and more realistic pre-supernova profiles using a high-resolution shock-capturing scheme and an approximate prescription for the nuclear equation of state. The most promising sources of scalar radiation are protoneutron stars collapsing to black holes. In case of a Galactic core collapse event forming a black hole, Advanced LIGO may be able to place independent constraints on the parameters of the theory at a level comparable to current Solar-System and binary-pulsar measurements. In the region of the parameter space admitting spontaneously scalarised stars, tr...
General degeneracy in density functional perturbation theory
Palenik, Mark C
2016-01-01
Degenerate perturbation theory from quantum mechanics is inadequate in density functional theory (DFT) because of nonlinearity in the Kohn-Sham potential. We develop the fully general degenerate perturbation theory for DFT without assuming that the degeneracy is required by symmetry. The resulting methodology is applied to the iron atom ground state in order to demonstrate the effects of degeneracy that appears both due to symmetry requirements and accidentally, between different representations of the symmetry group.
First test of Verlinde's theory of emergent gravity using weak gravitational lensing measurements
Brouwer, Margot M.; Visser, Manus R.; Dvornik, Andrej; Hoekstra, Henk; Kuijken, Konrad; Valentijn, Edwin A.; Bilicki, Maciej; Blake, Chris; Brough, Sarah; Buddelmeijer, Hugo; Erben, Thomas; Heymans, Catherine; Hildebrandt, Hendrik; Holwerda, Benne W.; Hopkins, Andrew M.; Klaes, Dominik; Liske, Jochen; Loveday, Jon; McFarland, John; Nakajima, Reiko; Sifón, Cristóbal; Taylor, Edward N.
2017-01-01
Verlinde proposed that the observed excess gravity in galaxies and clusters is the consequence of emergent gravity (EG). In this theory, the standard gravitational laws are modified on galactic and larger scales due to the displacement of dark energy by baryonic matter. EG gives an estimate of the e
Wald's gravitational entropy for ghost-free, infinite derivative theories of Gravity
Conroy, Aindriú; Teimouri, Ali
2015-01-01
In this paper, we demonstrate that the Wald's entropy for any spherically symmetric blackhole within an infinite derivative theory of gravity is determined solely by the area law. Thus, the infrared behaviour of gravity is captured by the Einstein-Hilbert term, provided that the massless graviton remains the only propagating degree of freedom in the spacetime.
Superfield quantization of general gauge theories
Lavrov, P M
1995-01-01
A superfield version on superspace (x^\\mu,\\theta^a) is proposed for the Sp(2)-- covariant Lagrangian quantization of general gauge theories. The BRST- and antiBRST- transformations are realized on superfields as supertranslations in the \\theta^a-- directions. A new (geometric) interpretation of the Ward identities in the quantum gauge theory is given.
BRST symmetry in the general gauge theories
Hyuk-Jae, Lee; Jae, Hyung, Yee
1994-01-01
By using the residual gauge symmetry interpretation of BRST invariance we have constructed a new BRST formulation for general gauge theories including those with open algebras. For theories with open gauge algebra the formulation leads to a BRST invariant effective action which does not contain any higher order terms in the ghost fields.
Inflation in general covariant Ho\\v{r}ava-Lifshitz gravity without projectability
Zhu, Tao; Wang, Anzhong
2012-01-01
In this paper, we study inflation in the general covariant Ho\\v{r}ava-Lifshitz gravity without the projectability condition. We write down explicitly the equations of the linear scalar perturbations of the FRW universe for a single scalar field without specifying to any gauge. Applying these equations to a particular gauge, we are able to obtain a master equation of the perturbations, in contrast to all the other versions of the theory without the projectability condition. This is because in the current version of the theory it has the same degree of freedom of general relativity. To calculate the power spectrum and index, we first define the initial conditions as the ones that minimize the energy of the ground state. Then, we obtain the full solutions of the equation of motion, by using the WKB approximations. From these solutions, we calculate the power spectrum and spectrum index of the comoving curvature perturbations and find the corrections due to the high order spatial derivative terms of the theory to...
Modified Gravity: the CMB, Weak Lensing and General Parameterisations
Thomas, Shaun A; Weller, Jochen
2011-01-01
We examine general physical parameterisations for viable gravitational models in the $f(R)$ framework. This is related to the mass of an additional scalar field, called the scalaron, that is introduced by the theories. Using a simple parameterisation for the scalaron mass $M(a)$ we show there is an exact correspondence between the model and popular parameterisations of the modified Poisson equation $\\mu(a,k)$ and the ratio of the Newtonian potentials $\\eta(a,k)$. However, by comparing the aforementioned model against other viable scalaron theories we highlight that the common form of $\\mu(a,k)$ and $\\eta(a,k)$ in the literature does not accurately represent $f(R)$ behaviour. We subsequently construct an improved description for the scalaron mass (and therefore $\\mu(a,k)$ and $\\eta(a,k)$) which captures their essential features and has benefits derived from a more physical origin. We study the scalaron's observational signatures and show the modification to the background Friedmann equation and CMB power spect...
Mass Renormalization in String Theory: General States
Pius, Roji; Sen, Ashoke
2014-01-01
In a previous paper we described a procedure for computing the renormalized masses and S-matrix elements in bosonic string theory for a special class of massive states which do not mix with unphysical states under renormalization. In this paper we extend this result to general states in bosonic string theory, and argue that only the squares of renormalized physical masses appear as the locations of the poles of the S-matrix of other physical states. We also discuss generalizations to Neveu-Schwarz sector states in heterotic and superstring theories.
Gravitation experiments at Stanford. [using general relativity theory
Lipa, J. A.
1980-01-01
The experimental situation in post-Newtonian gravitation is briefly reviewed in order to reexamine the extent to which experiment supports or refutes general relativity. A description is given of the equivalence principle project, the gyroscope experiment, and the search for gravity waves. It is noted that even though some doubt has been cast on the value of the perihelion advance and the gravitational redshift as precise tests of general relativity in the past few years, many competing theories have been ruled out; in particular, the results from the Viking mission significantly reduce the credibility of the Brans-Dicke theory (Brans and Dicke, 1961). The dimensionless constant omega in this theory is now forced to exceed 50, while the value originally proposed was 6 (omega being infinity in general relativity). It is noted that the gyro experiment described is capable of putting much tighter limits on this parameter, and together with the other experiments in progress will help place gravitational theory on a firmer experimental footing.
Energy of the Universe in Bianchi-type I Models in Moller's Tetrad Theory of Gravity
Aydogdu, O; Aydogdu, Oktay; Salti, Mustafa
2005-01-01
In this paper, using the energy definition in Moller's tetrad theory of gravity we calculate the total energy of the universe in Bianchi-type I cosmological models which includes both the matter and gravitational fields. The total energy is found to be zero and this result agrees with a previous works of Banerjee-Sen who investigated this problem using the general relativity version of the Einstein energy-momentum complex and Xulu who investigated same problem using the general relativity versions of the Landau-lifshitz, Papapetrou and Weinberg's energy-momentum complexes. The result that total energy of the universe in Bianchi-type I universes is zero supports the viewpoint of Tryon.
Generalized extended Navier-Stokes theory
DEFF Research Database (Denmark)
Hansen, J. S.; Daivis, Peter J.; Dyre, Jeppe C.
2013-01-01
in molecular fluids. To discuss these phenomena in detail, molecular dynamics simulations of molecular chlorine are performed for three different state points. In general, the theory captures the behavior for small wavevector and frequencies as expected. For example, in the hydrodynamic regime......The extended Navier-Stokes theory accounts for the coupling between the translational and rotational molecular degrees of freedom. In this paper, we generalize this theory to non-zero frequencies and wavevectors, which enables a new study of spatio-temporal correlation phenomena present...... and for molecular fluids with small moment of inertia like chlorine, the theory predicts that the longitudinal and transverse intrinsic angular velocity correlation functions are almost identical, which is also seen in the molecular dynamics simulations. However, the theory fails at large wavevector and frequencies...
A nonlinear theory of generalized functions
1990-01-01
This book provides a simple introduction to a nonlinear theory of generalized functions introduced by J.F. Colombeau, which gives a meaning to any multiplication of distributions. This theory extends from pure mathematics (it presents a faithful generalization of the classical theory of C? functions and provides a synthesis of most existing multiplications of distributions) to physics (it permits the resolution of ambiguities that appear in products of distributions), passing through the theory of partial differential equations both from the theoretical viewpoint (it furnishes a concept of weak solution of pde's leading to existence-uniqueness results in many cases where no distributional solution exists) and the numerical viewpoint (it introduces new and efficient methods developed recently in elastoplasticity, hydrodynamics and acoustics). This text presents basic concepts and results which until now were only published in article form. It is in- tended for mathematicians but, since the theory and applicati...
Sturmians and generalized sturmians in quantum theory
DEFF Research Database (Denmark)
Avery, John Scales; Avery, James Emil
2012-01-01
The theory of Sturmians and generalized Sturmians is reviewed. It is shown that when generalized Sturmians are used as basis functions, calculations on the spectra and physical properties of few-electron atoms can be performed with great ease and good accuracy. The use of many-center Coulomb Stur...
Energy Technology Data Exchange (ETDEWEB)
Marek-Crnjac, L. [Institute of Mathematics and Physics, University of Maribor (Slovenia)], E-mail: Leila.marek@guest.arnes.si; Iovane, G. [DIIMA - Universita di Salerno, Via Ponte don Melillo, 84084 Fisciano (Saudi Arabia) (Italy)], E-mail: iovane@diima.unisa.it; Nada, S.I. [Department of Mathematics, Faculty of Science, Qatar University (Qatar)], E-mail: snada@qu.edu.qa; Zhong, Ting [Department of Mathematics, Jishou University, 427000 Zhangjiajie, Hunan (China)], E-mail: zhongting_2005@126.com
2009-11-30
The present work gives first a review of the mathematical theory of finite and infinite dimensional topological spaces. Subsequently we connect the discussion with E-infinity theory and the theory of partially ordered sets. Finally, we contemplate the relevance of abstract results for quantum gravity.
Theory of gravity admitting arbitrary choice of the energy density level
Cherkas, S L
2016-01-01
We suggest a five-vectors theory of gravity admitting arbitrary choice of the energy density level. This theory is formulated as the constraint theory of the second kind, where the concrete values of Lagrange multipliers are evaluated. Cosmological implications of the model could be that the residual vacuum fluctuations dominate over all the universe evolution that resembles the Milne's universe.
Spin-Gauge Theory of Gravity with Higgs-field Mechanism
Dehnen, H
2013-01-01
We propose a Lorentz-covariant Yang-Mills spin-gauge theory, where the function valued Dirac matrices play the role of a non-scalar Higgs-field. As symmetry group we choose $SU(2) \\times U(1)$. After symmetry breaking a non-scalar Lorentz-covariant Higgs-field gravity appears, which can be interpreted within a classical limit as Einstein's metrical theory of gravity, where we restrict ourselves in a first step to its linearized version.
Scalar Gravitational Waves in the Effective Theory of Gravity
Mottola, Emil
2016-01-01
As a low energy effective field theory, classical General Relativity receives an infrared relevant modification from the conformal trace anomaly of the energy-momentum tensor of massless, or nearly massless, quantum fields. The local form of the effective action associated with the trace anomaly is expressed in terms of a dynamical scalar field that couples to the conformal factor of the spacetime metric, allowing it to propagate over macroscopic distances. Linearized around flat spacetime, this semi-classical EFT admits scalar gravitational wave solutions in addition to the transversely polarized tensor waves of the classical Einstein theory. The amplitude, Hamiltonian, energy flux, and quantization of the scalar wave modes are discussed. Astrophysical sources for scalar gravitational waves are considered, with the excited gluonic condensates in the interiors of neutron stars in merger events with other compact objects likely to provide the strongest burst signals.
Clear Evidence of a Continuum Theory of 4D Euclidean Simplicial Quantum Gravity
Egawa, H S; Yukawa, T
2002-01-01
Four-dimensional (4D) simplicial quantum gravity coupled to both scalar fields (N_X) and gauge fields (N_A) has been studied using Monte-Carlo simulations. The matter dependence of the string susceptibility exponent gamma^{(4)} is estimated. Furthermore, we compare our numerical results with Background-Metric-Independent (BMI) formulation conjectured to describe the quantum field theory of gravity in 4D. The numerical results suggest that the 4D simplicial quantum gravity is related to the conformal gravity in 4D. Therefore, we propose a phase structure in detail with adding both scalar and gauge fields and discuss the possibility and the property of a continuum theory of 4D Euclidean simplicial quantum gravity.
A theory of gravity with preferred frame and condensed matter interpretation
Schmelzer, I
2010-01-01
Does relativistic gravity provide empirical arguments against theories with a preferred frame like de Broglie-Bohm pilot wave theory? We present here a viable metric theory of gravity with preferred frame which gives a negative answer to this question. The theory has the same equations as Logunov's "relativistic theory of gravity" (RTG) but a less restrictive causality condition. It has not only a preferred frame, but allows even a condensed matter interpretation -- a variant of the ADM decomposition splits the metric into density, velocity and stress tensor of some hypothetical medium so that continuity and Euler equations hold. The theory shares many nice properties of RTG (EEP, Einstein equations in a natural limit, no big bang and black hole singularities, local energy and momentum densities for the gravitational field and a symmetry preference for a flat universe), but is also compatible with standard $\\Lambda$CDM cosmology. We also give a first principles derivation of the Lagrangian.
Hamiltonian approach to GR. Pt. 2. Covariant theory of quantum gravity
Energy Technology Data Exchange (ETDEWEB)
Cremaschini, Claudio [Faculty of Philosophy and Science, Silesian University in Opava, Institute of Physics and Research Center for Theoretical Physics and Astrophysics, Opava (Czech Republic); Tessarotto, Massimo [University of Trieste, Department of Mathematics and Geosciences, Trieste (Italy); Faculty of Philosophy and Science, Silesian University in Opava, Institute of Physics, Opava (Czech Republic)
2017-05-15
A non-perturbative quantum field theory of General Relativity is presented which leads to a new realization of the theory of covariant quantum gravity (CQG-theory). The treatment is founded on the recently identified Hamiltonian structure associated with the classical space-time, i.e., the corresponding manifestly covariant Hamilton equations and the related Hamilton-Jacobi theory. The quantum Hamiltonian operator and the CQG-wave equation for the corresponding CQG-state and wave function are realized in 4-scalar form. The new quantum wave equation is shown to be equivalent to a set of quantum hydrodynamic equations which warrant the consistency with the classical GR Hamilton-Jacobi equation in the semiclassical limit. A perturbative approximation scheme is developed, which permits the adoption of the harmonic oscillator approximation for the treatment of the Hamiltonian potential. As an application of the theory, the stationary vacuum CQG-wave equation is studied, yielding a stationary equation for the CQG-state in terms of the 4-scalar invariant-energy eigenvalue associated with the corresponding approximate quantum Hamiltonian operator. The conditions for the existence of a discrete invariant-energy spectrum are pointed out. This yields a possible estimate for the graviton mass together with a new interpretation about the quantum origin of the cosmological constant. (orig.)
Toward A Practical General Systems Methodological Theory
Nagib Callaos; Belkis Sánchez de Callaos
2003-01-01
Our main purpose in this paper is to describe the way in which we have been relating General System Theory (GST) to practice and to the design of a General Systems Methodology (GSM). Our first step was to apply GST to design a methodology for software development. Then, in a second step, by means of the experience/knowledge learned from applying the methodology to developing specific information systems, a continuous designing and re-designing process started, which simultaneously generalized...
Hamiltonian cosmological perturbation theory with loop quantum gravity corrections
Bojowald, M; Kagan, M; Singh, P; Skirzewski, A; Bojowald, Martin; Hern\\'andez, Hector H.; Kagan, Mikhail; Singh, Parampreet; Skirzewski, Aureliano
2006-01-01
Cosmological perturbation equations are derived systematically in a canonical scheme based on Ashtekar variables. A comparison with the covariant derivation and various subtleties in the calculation and choice of gauges are pointed out. Nevertheless, the treatment is more systematic when correction terms of canonical quantum gravity are to be included. This is done throughout the paper for one characteristic modification expected from loop quantum gravity.
Introduction to Loop Quantum Gravity
Mercuri, Simone
2010-01-01
The questions I have been asked during the 5th International School on Field Theory and Gravitation, have compelled me to give an account of the premises that I consider important for a beginner's approach to Loop Quantum Gravity. After a description of some general arguments and an introduction to the canonical theory of gravity, I review the background independent approach to quantum gravity, giving only a brief survey of Loop Quantum Gravity.
Energy in Theory of Gravity and Essence of Time
Pestov, I B
2005-01-01
In the framework of the field theory it is shown that a time (viewed as a scalar temporal field) is an internal property of the physical system, which defines its causal structure and evolution. A new concept of internal time allows to solve the energy problem in General Relativity and predicts the existence of matter outside the time. It is demonstrated that introduction of the temporal field permits to derive the physical laws of the electromagnetic field(the general covariant four dimensional Maxwell equations for the electric and magnetic fields) from the geometrical equations of this field. It means that the fundamental physical laws are in full correspondence with the essence of time. On this ground, from the geometrical laws of the gravitational field the physical evolution equations of this field are derived. Two characteristic solutions of these equations are obtained (including the Schwarzschild solution).
Gamow, George
2003-01-01
A distinguished physicist and teacher, George Gamow also possessed a special gift for making the intricacies of science accessible to a wide audience. In Gravity, he takes an enlightening look at three of the towering figures of science who unlocked many of the mysteries behind the laws of physics: Galileo, the first to take a close look at the process of free and restricted fall; Newton, originator of the concept of gravity as a universal force; and Einstein, who proposed that gravity is no more than the curvature of the four-dimensional space-time continuum.Graced with the author's own draw
Yang-Mills theory as bimetrical gravity: Polarization effects and finite-energy gluon clusters
Energy Technology Data Exchange (ETDEWEB)
Pavlovsky, Oleg V
2002-01-01
In this report a gravity representation of Yang-Mills theory is given. Using this approach, one obtains new information on solutions of classical YM theory. Singular solutions (black-hole-like solutions) of the YM equations are discussed in connection with bimetrical gravity. The behaviour of these solutions in a theory with a 'cosmological' Lambda-part is also investigated. A physical interpretation of such solutions is given. Using an effective field theory approach we try to show that quantum fluctuations and vacuum polarization effects lead to the generation of finite-energy objects in QCD.
Cosmic censorship in Lorentz-violating theories of gravity
Meiers, Michael; Saravani, Mehdi; Afshordi, Niayesh
2016-05-01
Is cosmic censorship special to general relativity, or can it survive a violation of local Lorentz invariance? Recent studies have shown that singularities in Lorentz -violating Einstein-Aether (or Horava-Lifshitz) theories can lie behind a universal horizon in simple black hole spacetimes. Even infinitely fast signals cannot escape these universal horizons. We extend this result, for an incompressible aether, to 3 +1 d dynamical or spinning spacetimes which possess inner Killing horizons, and show that a universal horizon always forms in between the outer and (would-be) inner horizons. This finding suggests a notion of cosmic censorship, given that geometry in these theories never evolves beyond the universal horizon (avoiding potentially singular inner Killing horizons). A surprising result is that there are 3 distinct possible stationary universal horizons for a spinning black hole, only one of which matches the dynamical spherical solution. This motivates dynamical studies of collapse in Einstein-Aether theories beyond spherical symmetry, which may reveal instabilities around the spherical solution.
Simple Recursion Relations for General Field Theories
Cheung, Clifford; Trnka, Jaroslav
2015-01-01
On-shell methods offer an alternative definition of quantum field theory at tree-level, replacing Feynman diagrams with recursion relations and interaction vertices with a handful of seed scattering amplitudes. In this paper we determine the simplest recursion relations needed to construct a general four-dimensional quantum field theory of massless particles. For this purpose we define a covering space of recursion relations which naturally generalizes all existing constructions, including those of BCFW and Risager. The validity of each recursion relation hinges on the large momentum behavior of an n-point scattering amplitude under an m-line momentum shift, which we determine solely from dimensional analysis, Lorentz invariance, and locality. We show that all amplitudes in a renormalizable theory are 5-line constructible. Amplitudes are 3-line constructible if an external particle carries spin or if the scalars in the theory carry equal charge under a global or gauge symmetry. Remarkably, this implies the 3-...
New formulation of Horava-Lifshitz quantum gravity as a master constraint theory
Soo, Chopin; Yu, Hoi-Lai
2010-01-01
Horava-Lifshitz theory of quantum gravity attempts to preserve unitarity by relinquishing space-time covariance, and improve renormalizability by including higher order (spatial) derivatives. For theories without full space-time covariance, departures of the constraint algebra from the Dirac algebra are to be expected. In the non-projectable version of Horava-Lifshitz gravity, the commutator of two local Hamiltonian constraints leads to severely restrictive secondary constraints and perplexing "troubles". On the other hand, the projectable version has an integrated Hamiltonian constraint and consistent constraint algebra. But an extra graviton mode which can be problematic is then allowed, whereas in Einstein's theory the spurious mode is eliminated precisely by the local Hamiltonian constraint. A new formulation of Horava-Lifshitz gravity, naturally realized as a representation of the master constraint algebra studied by loop quantum gravity researchers, is presented in this work. This reformulation yields a...
Chu, Chong-Sun
2016-01-01
We consider higher derivative gravity and obtain universal relations for the shape coefficients $(f_a, f_b, f_c)$ of the shape dependent universal part of the R\\'enyi entropy for four dimensional CFTs in terms of the parameters $(c, t_2, t_4)$ of two-point and three-point functions of stress tensors. As a consistency check, these shape coefficients $f_a$ and $f_c$ satisfy the differential relation as derived previously for the R\\'enyi entropy. Interestingly, these holographic relations also apply to weakly coupled conformal field theories such as theories of free fermions and vectors but are violated by theories of free scalars. The mismatch of $f_a$ for scalars has been observed in the literature and is due to certain delicate boundary contributions to the modular Hamiltonian. Interestingly, we find a combination of our holographic relations which are satisfied by all free CFTs including scalars. We conjecture that this combined relation is universal for general CFTs in four dimensional spacetime. Finally, w...
Indian Academy of Sciences (India)
Sezgin Aygün; İsmail Tarhan
2012-04-01
In this study we have investigated the energy–momentum distributions for homogeneous and anisotropic Bianchi type-IV in B class Universe. For this purpose, we have used energy–momentum complexes of Einstein, Bergmann–Thomson, Landau–Lifshitz (LL), Papapetrou, Tolman and Møller in general relativity (GR) as also Einstein, Bergmann–Thomson, Landau–Lifshitz and Møller in teleparallel gravity (TG). From the obtained results we have found that Einstein and Bergmann–Thomson distributions are exactly giving the same results in GR and TG but the Landau–Lifshitz, Papapetrou Tolman and Møller energy–momentum distributions do not provide the same results with Einstein and Bergmann–Thomson in GR and TG. Furthermore, Einstein, Bergmann–Thomson and LL results are the same in different gravitation theories and we get that both GR and TG are equivalent theories for these prescriptions. From the obtained solutions, we could say that these are equivalent theories. Also, Møller energy–momentum distributions do not give the same results in GR and TG. However, we have found that all energy prescriptions are negative and our results agree with Nester et al.
Can Dark Matter be an artifact of extended theories of gravity?
Choudhury, Sayantan; Sadhukhan, Soumya
2015-01-01
In this article, we propose different background models of extended theories of gravity, which are minimally coupled to the SM fields, to explain the possibility of genesis of dark matter without affecting the SM particle sector. We modify the gravity sector by allowing quantum corrections motivated from (1) local $f(R)$ gravity, (2) non local ghost free theory of gravity, and (3) non-minimally coupled gravity with SM sector and dilaton field. Next we apply conformal transformation on the metric to transform the action back to the Einstein frame. We also show that an effective theory constructed from these extended theories of gravity and SM sector looks exactly the same. Using the relic constraint observed by Planck 2015, we constrain the scale of the effective field theory ($\\Lambda_{UV}$) as well as the dark matter mass ($M$). We consider two cases- (1) light dark matter (LDM) and (2) heavy dark matter (HDM), and deduce upper bounds on thermally averaged cross section of dark matter annihilating to SM part...
A theory of generalized Bloch oscillations
DEFF Research Database (Denmark)
Duggen, Lars; Lew Yan Voon, L. C.; Lassen, Benny;
2016-01-01
Bloch oscillations of electrons are shown to occur for cases when the energy spectrum does not consist of the traditional evenly-spaced ladders and the potential gradient does not result from an external electric field. A theory of such generalized Bloch oscillations is presented and an exact cal...... oscillations. We stipulate that the presented theory of generalized Bloch oscillations can be extended to other systems such as acoustics and photonics.......Bloch oscillations of electrons are shown to occur for cases when the energy spectrum does not consist of the traditional evenly-spaced ladders and the potential gradient does not result from an external electric field. A theory of such generalized Bloch oscillations is presented and an exact...... calculation is given to confirm this phenomenon. Our results allow for a greater freedom of design for experimentally observing Bloch oscillations. For strongly coupled oscillator systems displaying Bloch oscillations, it is further demonstrated that reordering of oscillators leads to destruction of Bloch...
Classical Weyl Transverse Gravity
Oda, Ichiro
2016-01-01
We study various classical aspects of the Weyl transverse (WTDiff) gravity in a general space-time dimension. First of all, we clarify a classical equivalence among three kinds of gravitational theories, those are, the conformally-invariant scalar tensor gravity, Einstein's general relativity and the WTDiff gravity via the gauge fixing procedure. Secondly, we show that in the WTDiff gravity the cosmological constant is a mere integration constant as in unimodular gravity, but it does not receive any radiative corrections unlike the unimodular gravity. A key point in this proof is to construct a covariantly conserved energy-momentum tensor, which is achieved on the basis of this equivalence relation. Thirdly, we demonstrate that the Noether current for the Weyl transformation is identically vanishing, thereby implying that the Weyl symmetry existing in both the conformally-invariant scalar tensor gravity and the WTDiff gravity is a "fake" symmetry. We find it possible to extend this proof to all matter fields,...
Transition operators in electromagnetic-wave diffraction theory - General theory
Hahne, G. E.
1992-01-01
A formal theory is developed for the scattering of time-harmonic electromagnetic waves from impenetrable immobile obstacles with given linear, homogeneous, and generally nonlocal boundary conditions of Leontovich (impedance) type for the wave of the obstacle's surface. The theory is modeled on the complete Green's function and the transition (T) operator in time-independent formal scattering theory of nonrelativistic quantum mechanics. An expression for the differential scattering cross section for plane electromagnetic waves is derived in terms of certain matrix elements of the T operator for the obstacle.
Grounded Theory as a General Research Methodology
Directory of Open Access Journals (Sweden)
Judith A. Holton, Ph.D.
2008-06-01
Full Text Available Since its inception over forty years ago, grounded theory has achieved canonical status in the research world (Locke, 2001, p.1. Qualitative researchers, in particular, have embraced grounded theory although often without sufficient scholarship in the methodology (Partington, 2000, p.93; 2002, p.136. The embrace renders many researchers unable to perceive grounded theory as a general methodology and an alternative to the dominant qualitative and quantitative research paradigms. The result is methodological confusion and an often unconscious remodelling of the original methodology (Glaser, 2003. Given the various interpretations and approaches that have been popularised under the rubric of grounded theory, this paper addresses the important distinction between grounded theory as a general methodology and its popularisation as a qualitative research method. The paper begins with a brief overview of grounded theory’s origins and its philosophical foundations then continues by addressing the basic distinction between abstract conceptualisation as employed in classic grounded theory and the conceptual description approach as adopted by many qualitative researchers. The paper continues with a brief overview of the criteria for judging the quality of classic grounded theory and concludes by detailing its methodological principles.