Showing papers on "Gravitation published in 2000"
TL;DR: In this article, the authors propose a mechanism by which four-dimensional Newtonian gravity emerges on a 3-brane in 5D Minkowski space with an infinite size extra dimension.
3,247 citations
TL;DR: In this paper, the authors consider the brane world with a negative tension and derive the effective gravitational equations, which reduce to the conventional Einstein equations in the low energy limit, in which all the matter forces except gravity are confined on the 3-brane in a 5-dimensional spacetime with ${Z}_{2}$ symmetry.
Abstract: We carefully investigate the gravitational equations of the brane world, in which all the matter forces except gravity are confined on the 3-brane in a 5-dimensional spacetime with ${Z}_{2}$ symmetry. We derive the effective gravitational equations on the brane, which reduce to the conventional Einstein equations in the low energy limit. From our general argument we conclude that the first Randall-Sundrum-type theory predicts that the brane with a negative tension is an antigravity world and hence should be excluded from the physical point of view. Their second-type theory where the brane has a positive tension provides the correct signature of gravity. In this latter case, if the bulk spacetime is exactly anti--de Sitter spacetime, generically the matter on the brane is required to be spatially homogeneous because of the Bianchi identities. By allowing deviations from anti--de Sitter spacetime in the bulk, the situation will be relaxed and the Bianchi identities give just the relation between the Weyl tensor and the energy momentum tensor. In the present brane world scenario, the effective Einstein equations cease to be valid during an era when the cosmological constant on the brane is not well defined, such as in the case of the matter dominated by the potential energy of the scalar field.
1,350 citations
TL;DR: The present acceleration of the Universe strongly indicated by recent observational data can be modeled in the scope of a scalar-tensor theory of gravity by determining the structure of this theory along with the present density of dustlike matter from two observable cosmological functions.
Abstract: The present acceleration of the Universe strongly indicated by recent observational data can be modeled in the scope of a scalar-tensor theory of gravity. We show that it is possible to determine the structure of this theory along with the present density of dustlike matter from two observable cosmological functions: the luminosity distance and the linear density perturbation in the dustlike matter component as functions of redshift. Explicit results are presented in the first order in the small inverse Brans-Dicke parameter ${\ensuremath{\omega}}^{\ensuremath{-}1}$.
912 citations
TL;DR: In this paper, the authors study gravity in background that are smooth generalizations of the Randall-Sundrum model, with and without scalar fields, and show that the four-dimensional gravitational mode is localized precisely when the effects of the continuum modes decouple at distances larger than the Planck scale.
522 citations
TL;DR: In this article, a new approach to the cosmological constant problem is proposed, which makes essential use of an extra dimension, and the strong curvature region of the solutions may effectively cut off the size of the extra dimension and give rise to macroscopic 4D gravity.
443 citations
TL;DR: In this article, the authors explore the consequences of placing the Standard Model gauge fields in the bulk of the recently proposed localized gravity model of Randall and Sundrum and find that the Kaluza-Klein excitations of these fields are necessarily strongly coupled and demonstrate that current precision electroweak data constrain the lowest states to lie above ≃23 TeV.
432 citations
TL;DR: In this article, the authors consider an especially simple version of a thick domain wall in AdS space and investigate how four-dimensional gravity arises in this context, and demonstrate that there are no such resonances in the model they consider.
382 citations
01 Aug 2000
TL;DR: In this paper, a holographic principle for the cosmology is proposed, which dictates that the particle entropy within the cosmological apparent horizon should not exceed the gravitational entropy associated with the apparent horizon.
Abstract: A version of holographic principle for the cosmology is proposed, which dictates that the particle entropy within the cosmological apparent horizon should not exceed the gravitational entropy associated with the apparent horizon. It is shown that, in the Friedmann-Robertson-Walker (FRW) cosmology, the open Universe as well as a restricted class of flat cases are compatible with the principle, whereas closed Universe is not. It is also found that inflationary universe after the big-bang is incompatible with the cosmic holography.
382 citations
TL;DR: In this article, the authors derived the covariant nonlinear dynamical equations for the gravitational and matter fields on the brane, and then linearized to find the perturbation equations on the Brane.
Abstract: In Randall-Sundrum-type brane-world cosmologies, the dynamical equations on the three-brane differ from the general relativity equations by terms that carry the effects of embedding and of the free gravitational field in the five-dimensional bulk. Instead of starting from an ansatz for the metric, we derive the covariant nonlinear dynamical equations for the gravitational and matter fields on the brane, and then linearize to find the perturbation equations on the brane. The local energy-momentum corrections are significant only at very high energies. The imprint on the brane of the nonlocal gravitational field in the bulk is more subtle, and we provide a careful decomposition of this effect into nonlocal energy density, flux and anisotropic stress. The nonlocal energy density determines the tidal acceleration in the off-brane direction, and can oppose singularity formation via the generalized Raychaudhuri equation. Unlike the nonlocal energy density and flux, the nonlocal anisotropic stress is not determined by an evolution equation on the brane, reflecting the fact that brane observers cannot in general make predictions from initial data. In particular, isotropy of the cosmic microwave background may no longer guarantee a Friedmann geometry. Adiabatic density perturbations are coupled to perturbations in the nonlocal bulk field, and in general the system is not closed on the brane. But on super- Hubble scales, density perturbations satisfy a decoupled third-order equation, and can be evaluated by brane observers. Tensor perturbations on the brane are suppressed by local bulk effects during inflation, while nonlocal effects can serve as a source or a sink. Vorticity on the brane decays as in general relativity, but nonlocal bulk effects can source the gravito-magnetic field, so that vector perturbations can be generated in the absence of vorticity.
373 citations
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TL;DR: For a given dimension d, the Lagrangians under consideration are labeled by an integer k=1,2,...,[(d-1)/2] as mentioned in this paper.
Abstract: Gravitation theories selected by requiring that they have a unique anti-de Sitter vacuum with a fixed cosmological constant are studied. For a given dimension d, the Lagrangians under consideration are labeled by an integer k=1,2, . . . ,[(d-1)/2]. Black holes for each d and k are found and are used to rank these theories. A minimum possible size for a localized electrically charged source is predicted in the whole set of theories, except general relativity. It is found that the thermodynamic behavior falls into two classes: If d-2k=1, these solutions resemble the three dimensional black hole; otherwise, their behavior is similar to the Schwarzschild-AdS4 geometry. ©2000 The American Physical Society.
317 citations
TL;DR: In this article, the Bekenstein-Hawking area law for black hole entropy in the presence of higher-derivative interactions was extended to the case of supersymmetric black holes and their type-II duals.
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TL;DR: Kikkawa et al. as mentioned in this paper presented the picture that we live in a "brane world" (in the present-day terminology) i.e. in a dynamically localized 3-brane in a higher dimensional space.
Abstract: Here we place the TeX-typeset version of the old preprint SMC-PHYS-66 (1982), which was published in K. Akama, "Pregeometry", in Lecture Notes in Physics, 176, Gauge Theory and Gravitation, Proceedings, Nara, 1982, edited by K. Kikkawa, N. Nakanishi and H. Nariai, (Springer-Verlag) 267--271. In the paper, we presented the picture that we live in a "brane world" (in the present-day terminology) i.e. in a dynamically localized 3-brane in a higher dimensional space. We adopt, as an example, the dynamics of the Nielsen-Olesen vortex type in six dimensional spacetime to localize our space-time within a 3-brane. At low energies, everything is trapped in the 3-brane, and the Einstein gravity is induced through the fluctuations of the 3-brane. The idea is important because it provides a way basically distinct from the "compactification" to hide the extra dimensions which become necessary for various theoretical reasons.
TL;DR: A metric solution in six dimensions, where gravity is localized on a four-dimensional singular stringlike defect, where the corrections to four- dimensional gravity from the bulk continuum modes are suppressed by O(1/r(3).
Abstract: A study was carried out to determine what happens with gravity around a 3-brane of a specific structure in 6D spacetime with a negative cosmological constant. It was shown that there is a normalizible graviton zero mode attached to the stringlike defect, and the contribution of bulk gravitons is suppressed, leading to O(1/r3) violations of Newton's law. A hierarchy between the four-dimensional Planck scale and the Planck scale in 6D was derived.
01 Jan 2000
TL;DR: In this article, the authors describe the boundary state description of the N-body problem in Tetrad Gravity: a first step towards a Unified Description of the Four Interactions of the four interactions.
Abstract: General Perspectives.- Special Relativity at Action in the Universe.- String Theory and General Relativity.- Virgo - a Laser Interferometer for Gravitational Wave Detection.- A Space Test of General Relativity.- Canonical "Loop" Quantum Gravity and Spin Foam Models.- A Possible Way to Define an Effective Cosmological Constant in Scalar-Tensor Cosmologies.- A Microscopic Approach to Nuclear Physics: from Deuteron to Neutron Stars.- Perspectives in the Research of GravitationalWaves: Omnidirectional Resonant Detectors.- The Entropy of Black Holes via Noether's Theorem.- Dual Lagrangian Theories.- The Boundary State Description of D-Branes.- The N-body Problem in Tetrad Gravity: A First Step towards a Unified Description of the Four Interactions.- Applications of Calculus of Variations to General Relativity.- The Search for Gravitational Waves with Resonant Detectors.- Cauchy-Perturbative Matching and Outer Boundary Conditions.- Branes in Anti-de Sitter Space-Time.- Black Hole Entropy.- Gravitational Wave Astronomy from Space.- Bar Mode Instability in Relativistic Rotating Stars.- Recent Results.- General Relativity and Theory of Gravitation.- Theoretical Relativity: Classical Topics.- Why is the Gravitational Mass Equal to the Inertial Mass?.- Multiplicity of Timelike Geodesics in Splitting Lorentzian Manifolds.- Gravitational Collapse of Fluid Bodies and Cosmic Censorship: Analytic Insights.- Black Holes and Solitons.- The Prolongation Problem for the Heavenly Equation.- Time Extremizing Trajectories of Massive and Massless Objects in General Relativity.- Null Geodesics Joining Two Submanifolds in Stationary Lorentzian Manifolds.- Analytic Solution of Regge-Wheeler Differential Equation for Black Hole Perturbations in Radial Coordinate and Time Domains.- Quantum Gravity.- Problems in Quantum General Relativity and Gravitation.- Problems in Quantum General Relativity and Gravitation.- Foundational Problems in Quantum Gravity.- Foundational Problems in Quantum Gravity.- Foundational Problems in Quantum Gravity.- Foundational Problems in Quantum Gravity.- A Review of Recent Results of the ? -Function Regularization Procedure in Curved Spacetime.- Solitons in Three Space Dimensions as a Model for Relativistic Particles.- Relativistic Astrophysics and Cosmology.- Relativistic Astrophysics and Cosmology.- Voids in Open Universes.- Non-Stationary Accretion onto Black Holes.- Stochastic Backgrounds of Gravitational Waves from Compact Sources.- Experimental Gravitation.- Sights of Experimental Gravity.- Mechanical Isolation of Gravitational Wave Antennae: Present and Future.- Off-Line Subtraction of Seismic Newtonian Noise.- de Broglie-like Oscillation s of Spacetime.- Testing Newton's Inverse Square Law.
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TL;DR: In this paper, the authors investigate a consistent scenario of this type with two positive tension three-branes separated in a five-dimensional anti-de Sitter geometry, where the graviton is localized on the Planck brane, while a gapless continuum of additional gravity eigenmodes probe the infinitely large fifth dimension.
Abstract: In a non-trivial background geometry with extra dimensions, gravitational effects will depend on the shape of the Kaluza-Klein excitations of the graviton. We investigate a consistent scenario of this type with two positive tension three-branes separated in a five-dimensional anti-de Sitter geometry. The graviton is localized on the ``Planck'' brane, while a gapless continuum of additional gravity eigenmodes probe the infinitely large fifth dimension. Despite the background five-dimensional geometry, an observer confined to either brane sees gravity as essentially four-dimensional up to a position-dependent strong coupling scale, no matter where the brane is located. We apply this scenario to generate the TeV scale as a hierarchically suppressed mass scale. Arbitrarily light gravitational modes appear in this scenario, but with suppressed couplings. Real emission of these modes is observable at future colliders; the effects are similar to those produced by six large toroidal dimensions.
TL;DR: In this article, a review of recent developments in cosmology, cosmology and unification physics can be found, including the success and failures of "anthropic" reasoning in this context, and the prediction that the correct unification scheme will not allow calculation of (m d2m u)/m proton from first principles alone.
Abstract: Some properties of the world are fixed by physics derived from mathematical symmetries, while others are selected from an ensemble of possibilities. Several successes and failures of ‘‘anthropic’’ reasoning in this context are reviewed in light of recent developments in astrobiology, cosmology, and unification physics. Specific issues raised include our space-time location (including the reason for the present age of the universe), the time scale of biological evolution, the tuning of global cosmological parameters, and the origin of the Large Numbers of astrophysics and the parameters of the standard model. Out of the 20 parameters of the standard model, the basic behavior and structures of the world (nucleons, nuclei, atoms, molecules, planets, stars, galaxies) depend mainly on five of them: m e , m u , m d , a, and a G (where m proton and a QCD are taken as defined quantities). Three of these appear to be independent in the context of Grand Unified Theories (that is, not fixed by any known symmetry) and at the same time have values within a very narrow window which provides for stable nucleons and nuclei and abundant carbon. The conjecture is made that the two light quark masses and one coupling constant are ultimately determined even in the ‘‘final theory’’ by a choice from a large or continuous ensemble, and the prediction is offered that the correct unification scheme will not allow calculation of (m d2m u)/m proton from first principles alone.
TL;DR: In this article, discrete approaches to gravity, both classical and quantum, are reviewed, with emphasis on the method using piecewise-linear spaces, and progress in generalizing these models to four dimensions is discussed, as is the relationship of these models in both three and four dimensions to topological theories.
Abstract: Discrete approaches to gravity, both classical and quantum, are reviewed briefly, with emphasis on the method using piecewise-linear spaces. Models of three-dimensional quantum gravity involving 6j-symbols are then described, and progress in generalizing these models to four dimensions is discussed, as is the relationship of these models in both three and four dimensions to topological theories. Finally, the repercussions of the generalizations are explored for the original formulation of discrete gravity using edge-length variables.
TL;DR: In this article, the effects of low quantum gravity scale on string excited states of standard model particles were studied in a simple string model and the effect of these states on real and virtual graviton emission was analyzed.
Abstract: Arkani-Hamed, Dimopoulos, and Dvali have proposed that the fundamental gravitational scale is close to 1 TeV, and that the observed weakness of gravity at long distances is explained by the presence of large extra compact dimensions. If this scenario is realized in a string theory of quantum gravity, the string excited states of standard model particles will also have TeV masses. These states will be visible to experiment and in fact provide the first signatures of the presence of a low quantum gravity scale. Their presence also affects the more familiar signatures due to real and virtual graviton emission. We study the effects of these states in a simple string model. (c) 2000 The American Physical Society.
TL;DR: In this article, an exact lens equation without reference to a background spacetime is given for the case of Schwarzschild spacetime, where the light rays are geodesics of the background with sharp bending in the lens plane.
Abstract: (November 29, 1999)We propose a definition of an exact lens equation without reference to a background spacetime,and construct the exact lens equation explicitly in the case of Schwarzschild spacetime For theSchwarzschild case, we give exact expressions for the angular-diameter distance to the sources aswell as for the magnification factor and time of arrival of the images We compare the exactlens equation with the standard lens equation, derived under the thin-lens-weak-field assumption(where the light rays are geodesics of the background with sharp bending in the lens plane, andthe gravitational field is weak), and verify the fact that the standard weak-field thin-lens equationis inadequate at small impact parameter We show that the second-order correction to the weak-field thin-lens equation is inaccurate as well Finally, we compare the exact lens equation with therecently proposed strong-field thin-lens equation, obtained under the assumption of straight pathsbut without the small angle approximation, ie, with allowed large bending angles We show thatthe strong-field thin-lens equation is remarkably accurate, even for lightrays that take several turnsaround the lens before reaching the observerI INTRODUCTION
TL;DR: In this paper, the authors developed a method for renormalizing the AdS/CFT prescription for computing correlation functions, which involves regularizing the bulk on-shell supergravity action in a covariant way, computing all divergences, adding counterterms to cancel them and then removing the regulator.
Abstract: We develop a systematic method for renormalizing the AdS/CFT prescription for computing correlation functions. This involves regularizing the bulk on-shell supergravity action in a covariant way, computing all divergences, adding counterterms to cancel them and then removing the regulator. We explicitly work out the case of pure gravity up to six dimensions and of gravity coupled to scalars. The method can also be viewed as providing a holographic reconstruction of the bulk spacetime metric and of bulk fields on this spacetime, out of conformal field theory data. Knowing which sources are turned on is sufficient in order to obtain an asymptotic expansion of the bulk metric and of bulk fields near the boundary to high enough order so that all infrared divergences of the on-shell action are obtained. To continue the holographic reconstruction of the bulk fields one needs new CFT data: the expectation value of the dual operator. In particular, in order to obtain the bulk metric one needs to know the expectation value of stress-energy tensor of the boundary theory. We provide completely explicit formulae for the holographic stress-energy tensors up to six dimensions. We show that both the gravitational and matter conformal anomalies of the boundary theory are correctly reproduced. We also obtain the conformal transformation properties of the boundary stress-energy tensors.
TL;DR: It is shown that the spectrum of Kaluza-Klein modes is radically altered, which allows the early Universe to evolve normally up to substantial temperatures, and completely negates the astrophysical constraints on M(*.
Abstract: We reconsider theories with low gravitational (or string) scale M where Newton’s constant is generated via new large-volume spatial dimensions, while Standard Model states are localized to a 3brane. Utilizing compact hyperbolic manifolds (CHM’s) we show that the spectrum of Kaluza-Klein (KK) modes is radically altered. This allows an early universe cosmology with normal evolution up to substantial temperatures , and completely negates the constraints on M arising from astrophysics. Furthermore, an exponential hierarchy between the usual Planck scale and the true fundamental scale of physics can emerge with only O(1) coecients. The linear size of the internal space remains small. The proposal has striking testable signatures.
TL;DR: In this paper, the low energy effective action of gravity, induced by integrating out gauge and matter fields, in a general class of Randall-Sundrum type string compactification scenarios with exponential warp factors was studied.
Abstract: We study the low energy effective action $S$ of gravity, induced by integrating out gauge and matter fields, in a general class of Randall-Sundrum type string compactification scenarios with exponential warp factors. Our method combines dimensional reduction with the holographic map between between 5-d supergravity and 4-d large $N$ field theory. Using the classical supergravity approximation, we derive a flow equation of the effective action $S$ that controls its behavior under scale transformations. We find that as a result each extremum of $S$ automatically describes a complete RG trajectory of classical solutions. This implies that, provided the cosmological constant is canceled in the high energy theory, classical flat space backgrounds naturally remain stable under the RG-flow. The mechanism responsible for this stability is that the non-zero vacuum energy generated by possible phase transitions, is absorbed by a dynamical adjustment of the contraction rate of the warp factor.
TL;DR: In this article, it was shown that a non-minimally coupled scalar field with a positive curvature coupling ξ>0 can easily violate all the standard energy conditions, up to and including the averaged null energy condition (ANEC).
Abstract: We describe the different possibilities that a simple and apparently quite harmless classical scalar field theory provides to violate the energy conditions. We demonstrate that a non-minimally coupled scalar field with a positive curvature coupling ξ>0 can easily violate all the standard energy conditions, up to and including the averaged null energy condition (ANEC). Indeed, this violation of the ANEC suggests the possible existence of traversable wormholes supported by non-minimally coupled scalars. To investigate this possibility we derive the classical solutions for gravity plus a general (arbitrary ξ) massless non-minimally coupled scalar field, restricting attention to the static and spherically symmetric configurations. Among these classical solutions we find an entire branch of traversable wormholes for every ξ>0. (This includes and generalizes the case of conformal coupling ξ = (1/6) we considered in 1999 Phys. Lett. B 466 127-34.) For these traversable wormholes to exist we demonstrate that the scalar field must reach trans-Planckian values somewhere in the geometry. We discuss how this can be accommodated within the current state of the art regarding scalar fields in modern theoretical physics. We emphasize that these scalar field theories, and the traversable wormhole solutions we derive, are compatible with all known experimental constraints from both particle physics and gravity.
TL;DR: In this paper, the authors provide a simple Newtonian MHD calculation of the braking of differential rotation by magnetic fields and viscosity, where the star is idealized as a differentially rotating, infinite cylinder consisting of a homogeneous, incompressible conducting gas.
Abstract: Differentially rotating stars can support significantly more mass in equilibrium than nonrotating or uniformly rotating stars, according to general relativity. The remnant of a binary neutron star merger may give rise to such a "hypermassive" object. While such a star may be dynamically stable against gravitational collapse and bar formation, the radial stabilization due to differential rotation is likely to be temporary. Magnetic braking and viscosity combine to drive the star to uniform rotation, even if the seed magnetic field and the viscosity are small. This process inevitably leads to delayed collapse, which will be accompanied by a delayed gravitational wave burst and, possibly, a gamma-ray burst. We provide a simple, Newtonian MHD calculation of the braking of differential rotation by magnetic fields and viscosity. The star is idealized as a differentially rotating, infinite cylinder consisting of a homogeneous, incompressible conducting gas. We solve analytically the simplest case in which the gas has no viscosity and the star resides in an exterior vacuum. We treat numerically cases in which the gas has internal viscosity and the star is embedded in an exterior, low-density, conducting medium. Our evolution calculations are presented to stimulate more realistic MHD simulations in full 3 + 1 general relativity. They serve to identify some of the key physical and numerical parameters, scaling behavior, and competing timescales that characterize this important process.
TL;DR: In this article, the authors study the dynamics of branes in configurations where the brane is the edge of a single anti-de Sitter (AdS) space and the surface of a vacuum bubble expanding into a Schwarzschild or AdS-Schwarzschild bulk, and find solutions that resemble the standard Robertson-Walker cosmologies, although, in the latter, the evolution can be controlled by a mass parameter in the bulk metric.
Abstract: We study the dynamics of branes in configurations where (1) the brane is the edge of a single anti--de Sitter (AdS) space and (2) the brane is the surface of a vacuum bubble expanding into a Schwarzschild or AdS-Schwarzschild bulk. In both cases we find solutions that resemble the standard Robertson-Walker cosmologies, although, in the latter, the evolution can be controlled by a mass parameter in the bulk metric. We also include a term in the brane action for the scalar curvature. This term adds a contribution to the low-energy theory of gravity which does not need to affect the cosmology, but which is necessary for the surface of the vacuum bubble to recover four-dimensional gravity.
16 Mar 2000
TL;DR: Gravitational radiation or gravitational waves as mentioned in this paper is one of the fundamental forces of Nature and it is the dominant force in most astronomical systems in which gravity must obey the principles of special relativity In particular, gravitational forces must not be transmitted or communicated faster than light.
Abstract: Gravity is one of the fundamental forces of Nature, and it is the dominant force in most astronomical systems In common with all other phenomena, gravity must obey the principles of special relativity In particular, gravitational forces must not be transmitted or communicated faster than light This means that when the gravitational field of an object changes, the changes ripple outwards through space and take a finite time to reach other objects These ripples are called gravitational radiation or gravitational waves This article gives a brief introduction to the physics of gravitational radiation, including technical material suitable for non-specialist scientists
TL;DR: In this article, the dynamical stability against bar-mode deformation of rapidly spinning neutron stars with diUerential rotation was studied and it was shown that stars above a critical value of b 4 T /W (where T is the rotational kinetic energy and W the gravita-tional binding energy) are dynamically unstable to bar formation.
Abstract: We study the dynamical stability against bar-mode deformation of rapidly spinning neutron stars with diUerential rotation. We perform fully relativistic three-dimensional simulations of compact stars with M/R " 0.1, where M is the total gravitational mass and R the equatorial circumferential radius. We adopt an adiabatic equation of state with adiabatic index ! \ 2. As in Newtonian theory, we —nd that stars above a critical value of b 4 T /W (where T is the rotational kinetic energy and W the gravita- tional binding energy) are dynamically unstable to bar formation. For our adopted choices of stellar compaction and rotation pro—le, the critical value of is D0.24¨0.25, only slightly smaller than b \ b dGR the well-known Newtonian value D0.27 for incompressible Maclaurin spheroids. The critical value depends only very weakly on the degree of diUerential rotation for the moderate range we surveyed. All unstable stars form bars on a dynamical timescale. Models with sufficiently large b subsequently form spiral arms and eject mass, driving the remnant to a dynamically stable state. Models with moderately large do not develop spiral arms or eject mass but adjust to form dynamically stable b Z b dGR ellipsoidal-like con—gurations. If the bar-mode instability is triggered in supernova collapse or binary neutron star mergers, it could be a strong and observable source of gravitational waves. We determine characteristic wave amplitudes and frequencies. Subject headings: dense matterrelativitystars: neutronstars: rotation
TL;DR: In this article, the stability of dilatonic AdS spaces due to quantum effects of dilaton coupled conformal matter is considered and the effective equation solution for a 5D AdS universe with a warp scale factor is found.
Abstract: The stability of dilatonic AdS spaces due to quantum effects of dilaton coupled conformal matter is considered. When such spaces do not exist on a classical level, their dynamical generation occurs. Explicit examples corresponding to the quantum creation of a 4D dilatonic AdS universe and a 2D dilatonic AdS black hole (BH) are presented. Motivated by the holographic RG, in a similar approach, the complete 5D effective action is discussed. The intermediate region where it is the sum of two parts, the bulk (classical gravity) and boundary quantum action, is investigated. The effective equation solution representing a 5D AdS universe with a warp scale factor is found. A four-dimensional de Sitter or AdS world is generated on the boundary of such a universe as a result of quantum effects.
TL;DR: Direct Integration of the Relaxed Einstein Equations (DIRE) as mentioned in this paper is a self-contained framework for calculating equations of motion and gravitational radiation emission for isolated gravitating systems based on the post-Newtonian approximation.
Abstract: We present a self-contained framework called Direct Integration of the Relaxed Einstein Equations (DIRE) for calculating equations of motion and gravitational radiation emission for isolated gravitating systems based on the post-Newtonian approximation. We cast the Einstein equations into their ``relaxed'' form of a flat-spacetime wave equation together with a harmonic gauge condition, and solve the equations formally as a retarded integral over the past null cone of the field point (chosen to be within the near zone when calculating equations of motion, and in the far zone when calculating gravitational radiation). The ``inner'' part of this integral(within a sphere of radius $\cal R \sim$ one gravitational wavelength) is approximated in a slow-motion expansion using standard techniques; the ``outer'' part, extending over the radiation zone, is evaluated using a null integration variable. We show generally and explicitly that all contributions to the inner integrals that depend on $\cal R$ cancel corresponding terms from the outer integrals, and that the outer integrals converge at infinity, subject only to reasonable assumptions about the past behavior of the source. The method cures defects that plagued previous ``brute-force'' slow-motion approaches to motion and gravitational radiation for isolated systems. We detail the procedure for iterating the solutions in a weak-field, slow-motion approximation, and derive expressions for the near-zone field through 3.5 post-Newtonian order in terms of Poisson-like potentials.
TL;DR: In this article, the authors propose definitions for covariance and local Lorentz invariance applicable when the speed of light $c$ is allowed to vary, and discuss some possibilities for invariant actions governing the dynamics of such theories.
Abstract: We propose definitions for covariance and local Lorentz invariance applicable when the speed of light $c$ is allowed to vary. They have the merit of retaining only those aspects of the usual definitions which are invariant under unit transformations, and which can therefore legitimately represent the outcome of an experiment. We then discuss some possibilities for invariant actions governing the dynamics of such theories. We consider first the classical action for matter fields and the effects of a changing $c$ upon quantization. We discover a peculiar form of quantum particle creation due to a varying $c$. We then study actions governing the dynamics of gravitation and the speed of light. We find the free, empty-space, no-gravity solution, to be interpreted as the counterpart of Minkowksi space-time, and highlight its similarities with Fock-Lorentz space-time. We also find flat-space string-type solutions, in which near the string core $c$ is much higher. We label them fast-tracks and compare them with gravitational wormholes. We finally discuss general features of cosmological and black hole solutions, and digress on the meaning of singularities in these theories.