Showing papers on "Friedmann–Lemaître–Robertson–Walker metric published in 1989"
TL;DR: In this article, the dynamics of the standard gravitational action without a cosmological constant were analyzed from the point of view of constrained hamiltonian systems, and it was observed that contrary to what one might think, the theory is fully covariant and contains only one overall degree of freedom (the cosmologically constant) in addition to the two degrees of freedom per point of ordinary Einstein's theory.
483 citations
TL;DR: Second-order propagation equations are derived for covariant and gauge-invariant quantities that characterize density inhomogeneities in an almost-uniform model universe in a transparent way and enable a unified and transparent derivation of a series of results in the literature.
Abstract: In the preceding paper, covariant and gauge-invariant quantities were defined that characterize density inhomogeneities in an almost-uniform model universe in a transparent way. In this paper second-order propagation equations are derived for these quantities in the case of a general perfect fluid,'' and their properties examined. We do not use a harmonic decomposition in our definitions, but when such a decomposition is applied, our results are compatible with those obtained by Bardeen in his harmonically based gauge-invariant analysis. Our second-order equation enables a unified and transparent derivation of a series of results in the literature, without any ambiguity from choice of any particular gauge.
145 citations
TL;DR: Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmological models were derived in Lyra's manifold assuming a time dependent displacement field in this paper, which solved the singularity, entropy and horizon problems which exist in the standard models of cosmology based on Riemannian geometry.
Abstract: Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmological models are derived in Lyra's manifold assuming a time dependent displacement field. The models obtained solve the singularity, entropy and horizon problems which exist in the standard models of cosmology based on Riemannian geometry. The asymptotic behaviour of the models is also examined. 1.
74 citations
TL;DR: In this article, it was shown that constant bulk viscosity leads to an inflationary solution for large values of the Brans-Dicke coupling parameter w.r.t.
Abstract: Exact cosmological solutions of the field equations in Brans-Dicke (BD) theory, with k = 0, FRW metric have been obtained in the presence of bulk viscosity. It is found that constant bulk viscosity leads to an inflationary solution for large values of the BD coupling parameter w. The case of radiative bulk viscosity during the decoupling era is investigated and the production of entropy is estimated.
66 citations
TL;DR: In this article, the Euclidian Einstein equations with a cosmological constant and a conformally coupled scalar field are solved, taking the metric to be of the Robertson-Walker type.
Abstract: The Euclidian Einstein equations with a cosmological constant and a conformally coupled scalar field are solved, taking the metric to be of the Robertson-Walker type. In the case Lambda = 0, solutions are found which represent a wormhole connecting two asymptotically flat Euclidian regions. In the case Lambda greater than 0, the solutions represent tunneling from a small Tolman-like universe to a large Robertson-Walker universe.
63 citations
TL;DR: A link is made between the existence of gravitational-wave modes and the conformal curvature of hypersurfaces in spacetime and how these results can be useful in the analysis of exact solutions of the Einstein field equations.
Abstract: We use Bardeen's gauge-invariant formalism to analyze the behavior of, and relationship between, various geometric and physical quantities of cosmological interest at the linear level. This leads to a cosmologically oriented gauge-invariant characterization of the different perturbation modes that can arise. In particular a link is made between the existence of gravitational-wave modes and the conformal curvature of hypersurfaces in spacetime. We indicate how these results can be useful in the analysis of exact solutions of the Einstein field equations.
42 citations
TL;DR: In this paper, the total decay probabilities for electron-positron pairs were evaluated in a spatially flat Robertson-Walker universe with time-reversed photon creation in a time-dependent external gravitational field.
38 citations
TL;DR: In this paper, it is shown that these integral constraints are the same in the case of spherical symmetry, and they are interpreted as fitting conditions, that is, as constraints on the background Robertson-Walker model rather than on the nature of inhomogeneities.
Abstract: Integral constraints occur in the case of spherically symmetric inhomogeneities in Robertson-Walker universes, and (according to Traschen) in the case of general perturbations of these models. It is shown that these constraints are the same in the case of spherical symmetry, and they are interpreted as 'fitting conditions', that is, as constraints on the background Robertson-Walker model rather than on the nature of inhomogeneities. These integral constraints significantly affect the interpretation of anisotropies in the cosmic microwave background radiation. 22 refs.
18 citations
TL;DR: In this article, a coordinate representation is introduced which unites all three cases into a single two-parameter family, and the limiting transitions to the Friedman-Lemaitre-Robertson-Walker (FLRW) models and to the Schwarzschild-de Sitter-like solutions are presented.
Abstract: Shear‐free normal cosmological models are the perfect fluid solutions of Einstein’s equations in which rotation and shear vanish, and which are not static [they were all found by A. Barnes, Gen. Relativ. Gravit. 4, 105 (1973)]. They are either spherically, plane, or hyperbolically symmetric. Their symmetries are discussed in various coordinate systems and related to the conformal group of the three‐dimensional flat space. A coordinate representation is introduced which unites all three cases into a single two‐parameter family. The limiting transitions to the Friedman–Lemaitre–Robertson–Walker (FLRW) models and to the Schwarzschild–de Sitter‐like solutions are presented.
16 citations
TL;DR: The thermodynamic behavior of the inhomogeneous Szekeres-type cosmologies with a perfect fluid as the source of gravitation is examined in this article. But it does not coincide with the law of temperature satisfied by the FRW universes, even asymptotically.
Abstract: The thermodynamic behaviour of the inhomogeneous Szekeres-type cosmologies (1971) with a perfect fluid as the source of gravitation is examined. Since the matter motion is geodetic, the absence of heat flow implies that the temperature is a function of time alone. For a subclass approaching homogeneity and isotropy at large cosmological times an expression for the temperature is derived. It does not coincide with the law of temperature satisfied by the FRW universes, even asymptotically. However, by assuming an equation of state explicitly dependent on the space coordinates, it is shown that the FRW thermodynamics may be recovered. In all cases the Euler and Gibbs-Duhem relations are no longer valid.
12 citations
TL;DR: In this paper, the existence of rotating cosmological objects coupled with a zero-mass scalar field has been investigated and exact solutions for the metric rotation Ω(r, t) under different conditions are obtained and their nature and role are investigated.
Abstract: Certain new analytic solutions for rotating perfect-fluid spheres in the Robertson-Walker universe are found out to substantiate the possibility of the existence of rotating cosmological objects coupled with zero-mass scalar field. Exact solutions for the metric rotation Ω(r, t) and the matter rotation ω(r, t) under different conditions are obtained and their nature and role are investigated. Except for perfect dragging the scalar field is found to have a damping effect on the rotation of matter. In some solutions we find out the restrictions on the radii of the models for realistic astrophysical situations. Rotating models which can also be expanding are also obtained, in which case the rotational velocities are found to decay with the time; and these models may be taken as examples of real astrophysical objects in the Universe.
TL;DR: In this article, the usual FRW hot big-bang cosmologies have been generalized by considering the equation of state ϱ=Anm+(γ−1)-1p, where m is the rest mass of the fluid particles and A is a dimensionless constant.
TL;DR: In this article, a generalized Kerr-NUT type metric is considered in connection with Einstein field equations corresponding to perfect fluid plus a pure radiation field, and a general scheme for obtaining the exact solutions of these field equations is developed.
Abstract: A generalized Kerr-NUT type metric is considered in connection with Einstein field equations corresponding to perfect fluid plus a pure radiation field. A general scheme for obtaining the exact solutions of these field equations is developed. Two physically meaningful particular cases are investigated in detail. One gives the field of a radiating Kerr particle embedded in the Einstein universe. The other solution may probably represent a deSitter-like universe pervaded by a pure radiation field.
TL;DR: In this article, an explicit calculation of a Wigner function including approximative quantum corrections in spacetimes is presented and the connection of this result to quantum field theory is discussed in some detail.
Abstract: An explicit calculation of a Wigner function including approximative quantum corrections in spacetimes is presented. The connection of this result to quantum field theory is discussed in some detail.
TL;DR: In this article, the cosmological implications of a D-dimensional Kaluza-Klein theory based on Euler form actions are investigated, where the D -dimensional manifold is taken to be a direct product of a Robertson-Walker space-time and an irreducible homogeneous internal space.
TL;DR: In this paper, the dynamical system approach is applied to the study of dynamics of multidimensional cosmological models with topology FRW ×TD (D-dimensional torus) in the presence of high-temperature quantum effects.
Abstract: The dynamical system approach is applied to the study of dynamics of multidimensional cosmological models with topology FRW ×TD (D-dimensional torus) in the presence of high-temperature quantum effects The stability methods developed in the paper of Szydlowski (Gen Rel Grav,20, 221, 1988) are used in the analysis of typical states of the metric in the neighborhood of singularities and for large time values The problems of dynamical dimensional reduction, structure of singularities, isotropization, etc, are discussed in this context
TL;DR: By considering the Robertson-Walker line element exact cosmological solutions have been obtained by taking spin-half-generated particles as matter sources in the Jordan-Brans-Dicke theory as discussed by the authors.
Abstract: By considering the Robertson-Walker line element exact cosmological solutions have been obtained by taking spin-half-generated particles as matter sources in the Jordan-Brans-Dicke theory. There exist exact solutions for which the ‘gravitational constant’ decreases linearly with time and the mass of the Universe increases proportionally to the square of its age while the density decreases with time. The results have been studied corresponding to the three values of curvature index. It has been shown that the expansion law is determined by the particles created by the expansion itself.
TL;DR: In this paper, the cosmological solutions in the six-dimensional Einstein-gauge theory were presented, with the addition of a matter term, and the general behavior of the scale factors of the ordinary (R3) and extra (R2) dimensions can be depicted in four stages.
TL;DR: In this article, the structure of the Gaussian effective potential for lambda phi 4 theory at finite temperature in a static closed Robertson-Walker universe was studied and the symmetry behaviour was also studied.
Abstract: The authors evaluate and study the structure of the Gaussian effective potential for lambda phi 4 theory at finite temperature in a static closed Robertson-Walker universe. The symmetry behaviour has also been studied within this framework.
TL;DR: In this paper, the authors solved the Klein-Gordon equation for a massive real scalar field in a non-singular spatially homogeneous and isotropic cosmological background which is tangent to Milne universes in the distant past and future (and hence asymptotically flat) and evolves between these two geometries via a phase of contraction to a point of maximum curvature followed by expansion.
Abstract: The authors solve the Klein-Gordon equation for a massive real scalar field in a non-singular spatially homogeneous and isotropic cosmological background which is tangent to Milne universes in the distant past and future (and hence asymptotically flat) and evolves between these two geometries via a phase of contraction to a point of maximum curvature followed by expansion. This allows a computation of the Bogolubov coefficients of the scalar field, usually interpreted as the rate of creation of matter by the time-varying gravitational field, either when the vacuum is defined at the moment of maximum curvature (the non-singular 'big bang') or at the beginning of the cosmic contraction. This new exact solution is compared with the results obtained when the geometry is that of a Milne universe.
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TL;DR: In this article, the first time that the general case of the Einstein equations has been solved, considering a non-null cosmological constant, nonnull tricurvature, and a large variety of equations of state represented by p = αρ (α = const), for a perfect fluid and the Robertson-Walker metric.
TL;DR: In this paper, a spatially flat R-W cosmological model with a massive scalar field was obtained for Einstein's field equations in the presence of a cosmologically constant.
Abstract: A spatially flat Robertson-Walker R-W cosmological model filled with a massive scalar field has been obtained for Einstein's field equations in the presence of a cosmological constant.
TL;DR: In this paper, the Friedmann-Robertson-Walker cosmological model was applied to the problem of zero-curvature cosmologies in which the source of the gravitational field is a comoving radiation field and a radial non-comoving imperfect fluid.
Abstract: Zero-curvature Friedmann-Robertson-Walker cosmological models that are exact solutions of Einstein's field equations and the laws of thermodynamics in which the source of the gravitational field is a comoving radiation field and a radial non-comoving imperfect fluid are investigated.
TL;DR: In this article, the maximum volume of the closed Friedmann closed universe in expansion was shown to be 2π2R3(t), instead of π2R 3(t) as found previously.
Abstract: The maximum volume of the closed Friedmann universe is further investigated and is shown to be 2π2R3(t), instead of π2R3(t) as found previously. This discrepancy comes from the incomplete use of the volume formula of 3-dimensional spherical space in the astronomical literature. Mathematically, there exists the maximum volume at any cosmic timet in a 3-dimensional spherical case. However, the Friedmann closed universe in expansion reaches its maximum volume only at the timet m of the maximum scale factorR(t m ). The particle horizon has no limitation for the farthest objects in the closed Friedmann universe if the proper distance of objects is compared with the particle horizon as it should be. It will lead to absurdity if the luminosity distance of objects is compared with the proper distance of the particle horizon.
TL;DR: In this paper, the authors investigated the isotropic FRM model with conventional perfect fluid matter and presented a wide class of exact solutions which avoid the singularities that appear in cosmological models based on Einstein's theory of gravitation.
Abstract: Within the framework of no-scale supergravity we investigate the isotropic FRM-model filled with conventional perfect fluid matter. We present a wide class of exact solutions which avoid the singularities that appear in cosmological models based on Einstein's theory of gravitation.
TL;DR: In this article, a study of imperfect fluid interacting with the gravitational field for spherically-symmetric Robertson-Walker metric has been carried out and exact solutions of the field equations of viscous fluid have been obtained under different equations of state.
Abstract: A study of imperfect fluid interacting with the gravitational field for spherically-symmetric Robertson-Walker metric has been carried out. Exact solutions of the field equations of viscous fluid have been obtained under different equations of state. The corresponding physical interpretations of the solutions have been investigated. It has been shown that the occurrence of Big-Bang does not take place when the viscous fluid as only source term interacts with the gravitational field at the initial stages.
TL;DR: In this article, the conformal factor and a massless scalar field are quantized on the Einstein background spacetime and a singularity-free cosmological model is obtained and discussed.
Abstract: The conformal factor and a massless scalar field are quantized on Einstein background spacetime. A singularity-free cosmological model is obtained and discussed.
TL;DR: In this article, the complete set of field equations in Brans-Dicke theory for a radiation-filled universe with Robertson-Walker metric was obtained and solved for a particular case.
Abstract: In a recent paper Singh and Deo obtained the field equations in Brans-Dicke theory for a radiation-filled universe with Robertson-Walker metric and solved the equations for a particular case. Here we obtain the complete set of solutions of these equations.
01 Jan 1989
TL;DR: A brief history of the cosmological constant is given in this article, where a general quantum field theory is still lacking, but also its solution lies with the understanding of vaccum energy.
Abstract: A brief history of the cosmological constant is given. Introduced and later discussed away by Einstein, recognized for its potential of defining cosmic time and tracing the history of the universe by Friedmann, the cosmological constant was first identified with negative vacuum density by Lemaitre. His interpretation was much later revived by Gliner whose work, together with the concept of a variable cosmological “constant” discussed by Linde on the basis of unified field theories, and the work of numerous other authors laid the foundations for the role the cosmological constant was to assume later: that of the very essence of inflationary theories of the universe. The unanswered problems which appear in this context remind us that a general quantum field theory is still lacking, but also that its solution lies with the understanding of vaccum energy, i.e. of Λ.