Showing papers on "Friedmann–Lemaître–Robertson–Walker metric published in 1992"
TL;DR: In this article, the cosmological constant problem is examined in the context of both astronomy and physics with reference to expansion dynamics, the age of the universe, distance measures, comoving density of objects, growth of linear perturbations, and gravitational lens probabilities.
Abstract: The cosmological constant problem is examined in the context of both astronomy and physics. Effects of a nonzero cosmological constant are discussed with reference to expansion dynamics, the age of the universe, distance measures, comoving density of objects, growth of linear perturbations, and gravitational lens probabilities. The observational status of the cosmological constant is reviewed, with attention given to the existence of high-redshift objects, age derivation from globular clusters and cosmic nuclear data, dynamical tests of Omega sub Lambda, quasar absorption line statistics, gravitational lensing, and astrophysics of distant objects. Finally, possible solutions to the physicist's cosmological constant problem are examined.
1,571 citations
TL;DR: In this article, the covariant and gauge-invariant perturbations of Robertson-Walker spacetimes are compared with the coordinate-based approach of Ellis and Bruni.
Abstract: This paper concerns gauge-invariant perturbations of Robertson-Walker spacetimes, with the aim of (1) giving a complete set of perturbation equations and (2) comparing the coordinate-based method of Bardeen with the covariant approach of Ellis and Bruni (1989). To this end, we first consider covariantly defined quantities which are gauge-invariant in a perturbed Robertson-Walker universe: for these variables we derive a complete set of covariant linearized equations as they follow from the Bianchi and Ricci identities, and we show various possible ways of obtaining a second-order linear equation for the density perturbation variables. Then we systematically expand the covariant and gauge-invariant variables, recovering Bardeen's variables as first-order terms in this expansion: thus the two sets of variables are equivalent to first order. Through this comparison Bardeen's variables are shown to have a natural physical and geometrical meaning, which can be determined without the need of a gauge specification, and Bardeen's equations follow directly.
251 citations
TL;DR: In this paper, the cosmological term Λ has been shown to be compatible with classical inflation for a wide class of functions G(t) and Λ(t).
Abstract: We consider Einstein's equations with variable gravitational couplingG and cosmological term Λ. For a power-law time-dependence ofG, the cosmological term varies in proportion to the inverse square of the time, provided the equation of state is not that of vacuum. There is then no dimensional constant associated with Λ. For a vacuum equation of state the model is compatible with classical inflation for a wide class of functionsG(t) and Λ(t). For non-power-law behaviour ofG(t), it is possible to have a scale factor that increases exponentially without a vacuum equation of state. For this case the energy density associated with Λ decreases exponentially, while at time zero it is equal with opposite sign to the regular energy density, so there is zero total energy initially.
156 citations
TL;DR: In this paper, it was shown that the classical Einstein field equations, suitably interpreted, allow a change of signature of spacetime, and specific examples of such changes are constructed in the case of Robertson-Walker geometries.
Abstract: The authors point out that the classical Einstein field equations, suitably interpreted, allow a change of signature of spacetime. Specific examples of such changes are constructed in the case of Robertson-Walker geometries. They obtain classical solutions that have properties similar to those obtained in quantum cosmologies obeying the Hartle-Hawking 'no boundary' condition: these singularity-free universes have no beginning, but they do have an origin of time. They can be regarded either as classical analogues of the quantum cosmology results, or as classical solutions where a quantum cosmology era is avoided.
147 citations
TL;DR: In this paper, a covariant formalism was introduced to treat inhomogeneities in any spacetime, and exact evolution equations were found for these variables, and the linearized form of these equations were obtained, showing that they give the standard results for a barotropic perfect fluid.
Abstract: In a series of recent papers, a new covariant formalism was introduced to treat inhomogeneities in any spacetime. The variables introduced in these papers are gauge-invariant with respect to a Robertson-Walker background spacetime because they vanish identically in such models, and they have a transparent physical meaning. Exact evolution equations were found for these variables, and the linearized form of these equations were obtained, showing that they give the standard results for a barotropic perfect fluid. In this paper we extent this formalism to the general case of multicomponent fluid sources with interactions between them
135 citations
TL;DR: In this paper, a new covariant and gauge-invariant (GI) treatment of perturbations in a Robertson-Walker universe dominated by a classical scalar field is proposed.
Abstract: The authors propose a new covariant and gauge-invariant (GI) treatment of perturbations in a Robertson-Walker universe dominated by a classical scalar field phi . They first set up the formalism, based on the natural slicing of the problem by the surfaces phi =constant, and introduce a set of covariantly defined GI variables. In their approach the whole inhomogeneity of the matter field is incorporated in the GI spatial fluctuations of the momentum psi of phi ; then the GI density perturbations are simply proportional to the momentum perturbations. The inhomogeneity of the geometry is characterized by GI fluctuations of the 3-curvature scalar of the surfaces phi =constant. The time evolution of the matter and curvature perturbations are coupled by a pair of first-order linear differential equations. Correspondingly, each GI variable satisfies a second-order linear homogeneous differential equation. When the background curvature vanishes, k=0, the curvature variable is conserved for perturbation scales larger than the horizon, but this is no longer true in general if k not=0. They discuss simple examples, including the case when more than one scalar field is present, recovering standard results for inflationary universe models. They also demonstrate that in coasting solutions with k=-1, inhomogeneities are damped out on all scales.
105 citations
TL;DR: The radiation and matter-dominated cosmologies associated with fourth-order conformal Weyl gravity, a theory which is currently being explored as a candidate alternative to the standard second-order Einstein theory, are presented in this article.
Abstract: The radiation and matter-dominated cosmologies associated with fourth-order conformal Weyl gravity, a theory which is currently being explored as a candidate alternative to the standard second-order Einstein theory, are presented. The theory naturally yields an open though nonetheless recollapsing universe which can even oscillate indefinitely, which appears to possess no flatness problem, which has a cosmology which could potentially be created out of nothing, which is singularity free, and which does not appear to require any cosmological dark matter.
60 citations
TL;DR: In this paper, a covariant formalism enabling the possibility of change of signature in classical General Relativity, when the geometry is that of a Robertson-Walker universe, is presented.
Abstract: This paper gives a covariant formalism enabling investigation of the possibility of change of signature in classical General Relativity, when the geometry is that of a Robertson-Walker universe. It is shown that such changes are compatible with the Einstein field equations, both in the case of a barotropic fluid and of a scalar field. A criterion is given for when such a change of signature should take place in the scalar field case. Some examples show the kind of resulting exact solutions of the field equations.
57 citations
TL;DR: The cosmological constant is a macroscopic parameter which controls the large-scale structure of the universe as mentioned in this paper, and it is a large discrepancy between theoretical expectation and empirical observation.
Abstract: The cosmological constant is a macroscopic parameter which controls the large-scale structure of the Universe. All observations to date have shown that it is very small. However, our modern microscopic theory of particle physics and gravity suggests that the cosmological constant should be very large. This discrepancy between theoretical expectation and empirical observation constitutes the cosmological constant problem. After a review of the problem, some approaches to its solution are briefly discussed, and then a possible solution is proposed. In this approach, the cosmological constant appears as a constant of integration, unrelated to any parameters in the Lagrangian. The solution makes crucial use of quantum mechanics.
52 citations
TL;DR: In this paper, the exact spherically symmetric solution of the Einstein field equations for dust (p=0) in observational coordinates for data on the past light cone C-(p0) consisting of redshifts, observer area distances, and galaxy number counts is given.
Abstract: The authors give the exact spherically symmetric solution of the Einstein field equations for dust (p=0) in observational coordinates for data on the past light cone C-(p0) consisting of redshifts, observer area distances, and galaxy number counts. A Bondi potential is found, which facilitates the integration. Also they show in detail how FLRW models can be constructed via these solutions from FLRW data. Finally, they discuss their approach with respect to other observationally oriented treatments, particularly those of Ehlers and Rindler (1987), and Rindler and Suson (1989).
45 citations
TL;DR: The wave functions for the Friedmann-Robertson-Walker (FRW) cosmology conformally and minimally coupled to a scalar field with a powerlaw potential or a polynomial potential are expanded in terms of the eigenfunctions of the Scalar field sub-Hamiltonian part.
Abstract: The expansion method by a time-dependent basis of the eigenfunctions for the space-coordinate-dependent sub-Hamiltonian is one of the most natural frameworks for quantum systems, relativistic as well as nonrelativistic. The complete set of wave functions is found in the product integral formulation, whose constants of integration are fixed by Cauchy initial data. The wave functions for the Friedmann-Robertson-Walker (FRW) cosmology conformally and minimally coupled to a scalar field with a powerlaw potential or a polynomial potential are expanded in terms of the eigenfunctions of the scalar field sub-Hamiltonian part
TL;DR: In this paper, the Brans-Dicke field equations in the presence of a cosmological term A were studied and the general solution of the field equations for arbitrary values of w and A was obtained.
Abstract: We study the Brans-Dicke vacuum field equations in the presence of a cosmological term A. Considering a Friedmann-Robertson-Walker metric with flat spatial sections (k=0), we provide a qualitative analysis of the solutions and investigate its asymptotic properties. The general solution of the field equations for arbitrary values ofw and A is obtained.
TL;DR: An exact solution of the field equations with a cosmological constant is given in this paper, describing a spherical-fronted impulsive gravitational wave propagating through the de Sitter universe.
TL;DR: Two exact cosmological solutions to a scalar-field potential motivated by six-dimensional (6D) Einstein-Maxwell theory are given, free of singularity and causality problems but conserves entropy.
Abstract: Two exact cosmological solutions to a scalar-field potential motivated by six-dimensional (6D) Einstein-Maxwell theory are given. The resulting pure scalar-field cosmology is free of singularity and causality problems but conserves entropy. These solutions are then extended into exact cosmological solutions for a decaying scalar field with an approximate two-loop 4D string potential. The resulting cosmology is, for both solutions, free of cosmological problems and close to the standard cosmology of the radiation era.
TL;DR: In this paper, the authors set up and solved the general first-order equations for dust relative to an FLRW background in observational coordinates using the fluid-ray tetrad formalism, with data on the past light cone C-(p0) consisting of galaxy redshifts, observer area distances, galaxy number counts and null shear measures.
Abstract: For pt.IV see ibid., vol.9, p.1711, (1992). The authors set up and solve the general (no symmetries assumed) first-order equations for dust (p=0) relative to an FLRW background in observational coordinates using the fluid-ray (FR) tetrad formalism, with data on the past light cone C-(p0) consisting of galaxy redshifts, observer area distances, galaxy number counts and null shear measures. Cosmological proper motions are not needed in the data set. A detailed framework for constructing solutions from any such data set is given, although no concrete solutions are presented. The character of these solutions will depend heavily on the data themselves.
TL;DR: In this paper, the authors solved the Einstein equations with a cosmological constant for those gravitational fields which have a reduced Ashtekar-spin holonomy group, and proved that the constant is a constant for all such fields.
Abstract: The author solves the Einstein equations with a cosmological constant for those gravitational fields which have a reduced Ashtekar-spin holonomy group.
TL;DR: In this paper, the authors show that it is possible to recover the form of the FLRW metric by averaging over inhomogeneities on a scale on which Einstein's equations are known to hold.
Abstract: Einstein's equations are averaged, first for a space-like distribution of stars, then for an expanding system of galaxies. The results indicate the possible nature of the extra terms introduced as in Ellis' conjecture, and also show that the rate of expansion is different from that of a FLRW model with comparable density. They also show that it is possible to recover the form of the FLRW metric by averaging over inhomogeneities on a scale on which Einstein's equations are known to hold.
TL;DR: In this article, the authors have obtained exact solutions for cosmological models in higher dimensions under different symmetries, assuming a homogeneous matter-energy content such that p = p ( t ) and d = d( t ).
TL;DR: In this article, the authors study dissipative Friedmann-Robertson-Walker (FRW) models with the help of the relativistic extended thermodynamics as formulated in the Landau-Lifshitz (energy) frame.
Abstract: The authors study dissipative Friedmann-Robertson-Walker (FRW) models with the help of the relativistic extended thermodynamics as formulated in the Landau-Lifshitz (energy) frame. The physically most relevant solutions are shown to tend asymptotically to models in which the initial material anisotropy due to the particle drift (diffusion) is washed out. Some recent results obtained by Turok (1988) and Barrow (1988) in a different context can be recovered.
TL;DR: In this paper, the dynamical equations for rotational perturbations of a Friedmann-Robertson-Walker universe containing a perfect fluid of massive matter and radiation together with relativistic collisionless matter are established.
Abstract: The dynamical equations for rotational (vector) perturbations of a Friedmann-Robertson-Walker universe containing a perfect fluid of massive matter and radiation together with relativistic collisionless matter are established. These equations have solutions which remain regular as the initial singularity is approached, in contrast to the purely perfect-fluid case, where small rotational perturbations cannot coexist with a Friedmann-type singularity due to the Helmholtz-Kelvin circulation theorem
TL;DR: Gravitational instability is expressed in terms of the dynamic systems theory and it is shown that in an open universe filled with matter of constant sound velocity the Jeans criterion does not adequately define the length scale of the gravitational structure.
Abstract: Gravitational instability is expressed in terms of the dynamic systems theory. The gauge-invariant Ellis-Bruni equation and Bardeen's equation are discussed in detail. It is shown that in an open universe filled with matter of constant sound velocity the Jeans criterion does not adequately define the length scale of the gravitational structure.
TL;DR: In this article, perfect fluid generalizations of the parabolic case of Szekeres class I solutions are interpreted as spacetimes whose matter source is a mixture of adiabatically interacting dust and a homogeneous perfect fluid (with density and pressure) and simple analytical solutions emerge when the dynamics of mu and p are governed by a Friedmann equation and the equation of state p=( gamma -1) mu holds.
Abstract: Perfect fluid generalizations of the parabolic case of Szekeres class I solutions are interpreted as spacetimes whose matter source is a mixture of adiabatically interacting dust (with density rho ) and a homogeneous perfect fluid (with density and pressure mu and p). Simple analytical solutions emerge when the dynamics of mu and p are governed by a Friedmann equation and the equation of state p=( gamma -1) mu holds. The Szafron models correspond to the dynamics of a spatially flat FRW cosmology, admitting a smooth matching with the latter along a suitable timelike hypersurface. New solutions arise for a homogeneous fluid satisfying spatially curved FRW dynamics. For slowly varying p and mu satisfying an arbitrary equation of state, approximate WKB type solutions are derived. Geometric properties and singularities are examined. All solutions are compatible with the existence of a 'regular centre' defined as the regular worldline of privileged isotropic observers. Some of the solutions admit evolution branches along with mu and rho are everywhere positive. These latter cases, under appropriate restrictions, could provide an adequate framework with which to model inhomogeneities in a cosmological background and other situations of astrophysical interest.
TL;DR: In this paper, the dynamic aspects of rotating and expanding cosmologies are investigated and exact solutions of GR and ECSK equations are obtained for the rotating universe and some distinctions are found between the FRW and rotating expanding models.
Abstract: We investigate the dynamic aspects of rotating and expanding cosmologies. Exact solutions of GR and ECSK equations are obtained. Cosmological scenarios are presented for the rotating universe. The common features and some distinctions are found between the FRW and rotating expanding models.
TL;DR: In this paper, the conditions for the existence of Newtonian analogs of a five dimensional generalization of the Friedman-Robertson-Walker (FRW) cosmological models in Wesson's gravitational theory are re-analyzed.
Abstract: The conditions for the existence of Newtonian analogs of a five dimensional (5D) generalization of the Friedman-Robertson-Walker (FRW) cosmological models in Wesson's gravitational theory are re-analyzed. Contrarily to other claims, we show that classical analogs can be obtained for non-null cosmological constant and negative or null spatial curvature.
TL;DR: The exact expression for the Dirac propagator for an arbitrary scale factor in the real-time formulation of finite-temperature field theory is found.
Abstract: We consider the Dirac field on a spatially flat Robertson-Walker space-time. We find the exact expression for the Dirac propagator for an arbitrary scale factor in the real-time formulation of finite-temperature field theory. The mode functions used in the construction satisfy uncoupled ordinary differential equations
TL;DR: In this paper, the Robertson-Walker and generalized pp-wave metrics were found to be consistent with conformal invariance of the supersymmetric σ-model beyond the two loop order.
TL;DR: The problem with solving for an exact embedding of a string in the manner of the Swiss-cheese model is examined in detail, and it is shown that the metric in the evacuated region around the string is unique.
Abstract: The embeddability of a straight cosmic string in a Friedmann-Robertson-Walker (FRW) universe is examined. Although previous suggestions that an exact embedding for a string with longitudinal tension equal to energy density is impossible are substantiated, it is shown that the deviations of either the external metric from the exact FRW metric or of the internal structure of the string from the exact tension equals energy density are expected to be very small, of the order of the square of the ratio of the string diameter (or the evacuated shell around the string) to the Hubble radius. Thus the lack of an exact mathematical embedding leads to negligible physical consequences. The problem with solving for an exact embedding of a string in the manner of the Swiss-cheese model is examined in detail, and it is shown that the metric in the evacuated region around the string is unique. That metric is determined to lowest order in the ratio of the evacuated region over the Hubble radius. The implications of this uniqueness for the Swiss-cheese embedding of a string are discussed.
TL;DR: In this article, the energy-momentum tensor expectation value in the vacuum defined through energy minimization is renormalizable and yields the usual anomalous trace in the massless limit of vector mesons.
TL;DR: In this paper, the cosmological model of extended inflation is reduced to a spatially flat Robertson-Walker geometry driven by a self-interacting scalar field with a potential of an exponential type.
Abstract: The authors reduce the cosmological model of extended inflation to a spatially flat Robertson-Walker geometry driven by a self-interacting scalar field with a potential of an exponential type. They quantize the gauge invariant scalar perturbations of the metric and the field, and compute the spectrum of the energy density fluctuations.