Showing papers on "Friedmann–Lemaître–Robertson–Walker metric published in 2009"
TL;DR: In this article, the authors considered the non-relativistic Ho\v{r}ava-Lifshitz four-dimensional theory of gravity and showed that it has the same Newtonian and post-Newtonian limits as GR and thus, it passes the classical tests.
411 citations
TL;DR: In this article, a cosmological reconstruction scheme for modified F(R) gravity is developed in terms of e-folding (or, redshift), which can be applied to any FRW cosmology.
342 citations
TL;DR: In this paper, the authors introduced a new infrared cut-off for the holographic dark energy and studied the correspondence between the quintessence, tachyon, K-essence and dilaton energy density in the flat FRW universe.
279 citations
TL;DR: In this paper, the authors proposed a renormalizable gravity theory in four dimensions which reduces to Einstein gravity with a non-vanishing cosmological constant in IR but with improved UV behaviors.
Abstract: Recently Horava proposed a renormalizable gravity theory in four dimensions which reduces to Einstein gravity with a non-vanishing cosmological constant in IR but with improved UV behaviors Here, I study an IR modification which breaks "softly" the detailed balance condition in Horava model and allows the asymptotically flat limit as well I obtain the black hole and cosmological solutions for "arbitrary" cosmological constant that represent the analogs of the standard Schwartzschild-(A)dS solutions which can be asymptotically (A)dS as well as flat and I discuss some thermodynamical properties I also obtain solutions for FRW metric with an arbitrary cosmological constant I study its implication to the dark energy and find that it seems to be consistent with current observational data
231 citations
TL;DR: In this paper, the authors proposed a renormalizable gravity theory in four dimensions which reduces to Einstein gravity with a non-vanishing cosmological constant in IR but with improved UV behaviors.
Abstract: Recently Ho?ava proposed a renormalizable gravity theory in four dimensions which reduces to Einstein gravity with a non-vanishing cosmological constant in IR but with improved UV behaviors. Here, I study an IR modification which breaks ``softly'' the detailed balance condition in Ho?ava model and allows the asymptotically flat limit as well. I obtain the black hole and cosmological solutions for ``arbitrary'' cosmological constant that represent the analogs of the standard Schwarzschild-(A)dS solutions which can be asymptotically (A)dS as well as flat and I discuss their thermodynamical properties. I also obtain solutions for FRW metric with an arbitrary cosmological constant. I study its implication to the dark energy and find that it seems to be consistent with current observational data.
186 citations
TL;DR: In this paper, the influence of generalized uncertainty principle and extended uncertainty principle on the thermodynamics of the Friedmann-Robertson-Walker (FRW) universe has been investigated, and it is shown that the entropy of the apparent horizon of the FRW universe gets a correction if one considers the effect of the GUP or EUP.
117 citations
TL;DR: In this article, the tachyon cosmology in non-interacting and interacting cases in a non-flat FRW universe is studied. And the potential and the dynamics of the tACHYON field are reconstructed.
111 citations
TL;DR: In this article, the authors consider a non-trivial test of the new gravity theory in FRW universe by considering an IR modification which breaks "softly" the detailed balance condition in the original Horava model.
Abstract: Recently Horava proposed a renormalizable gravity theory with higher spatial derivatives in four dimensions which reduces to Einstein gravity with a non-vanishing cosmological constant in IR but with improved UV behaviors. Here, I consider a non-trivial test of the new gravity theory in FRW universe by considering an IR modification which breaks "softly" the detailed balance condition in the original Horava model. I separate the dark energy parts from the usual Einstein gravity parts in the Friedman equations and obtain the formula of the equations of state parameter. The IR modified Horava gravity seems to be consistent with the current observational data but we need some more refined data sets to see whether the theory is really consistent with our universe. From the consistency of our theory, I obtain some constraints on the allowed values of w_0 and w_a in the Chevallier, Polarski, and Linder's parametrization and this may be tested in the near future, by sharpening the data sets.
90 citations
TL;DR: In this article, the dynamics of homogeneous isotropic FRW cosmologies with positive spatial curvature in f(R)-gravity were studied, paying special attention to the existence of Einstein static models.
Abstract: We study the dynamics of homogeneous isotropic FRW cosmologies with positive spatial curvature in f(R)-gravity, paying special attention to the existence of Einstein static models and only study forms of f(R) = Rn for which these static models have been shown to exist. We construct a compact state space and identify past and future attractors of the system and recover a previously discovered future attractor corresponding to an expanding accelerating model. We also discuss the existence of universes which have both a past and a future bounce, a phenomenon which is absent in general relativity.
89 citations
TL;DR: In this paper, the authors investigated cosmological particle production in spacetimes where Lorentz invariance emerges in the infrared limit, but is explicitly broken in the ultraviolet regime.
Abstract: We investigate cosmological particle production in spacetimes where Lorentz invariance emerges in the infrared limit, but is explicitly broken in the ultraviolet regime. Thus these models are similar to many (but not all) models of quantum gravity, where a breakdown of Lorentz invariance is expected for ultraviolet physics around the Planck/string scale. Our specific model focuses on the boost subgroup that supports CPT invariance and results in a momentum-dependent dispersion relation. Motivated by previous studies on spacetimes emerging from a microscopic substrate, we show how these modifications naturally lead to momentum-dependent rainbow metrics. Firstly, we investigate the possibility of reproducing cosmological particle production in spacetimes emerging from real Bose gases. Several papers have been written on the analogy between the kinematics of linearized perturbations in Bose–Einstein condensates and effective curved-spacetime quantum field theory. Recently we have studied the influence of nonperturbative ultraviolet corrections in time-dependent analog spacetimes, leading to momentum-dependent emergent rainbow spacetimes. We show that models involving a time-dependent microscopic interaction are suitable for mimicking quantum effects in FRW spacetimes. Within certain limits the analogy is sufficiently good to simulate relativistic quantum field theory in time-dependent classical backgrounds, and the quantum effects are approximately robust against the model-dependent modifications. Secondly, we analyze how significantly the particle production process deviates from the common picture. While very low-energy modes do not see the difference at all, some modes 're-enter the Hubble horizon' during the inflationary epoch, and extreme ultraviolet modes are completely insensitive to the expansion. The analysis outlined here, because it is nonperturbative in the rainbow metric, exhibits features that cannot be extracted simply from the standard perturbative modification of particle dispersion relations. However, we also show how the final result, after many e-foldings, will approach a time-independent exponentially decaying particle spectrum.
72 citations
TL;DR: In this article, a Hamilton-Jacobi method beyond the semiclassical approximation in black hole physics was developed by Banerjee and Majhi, and they generalize their analysis of black holes to the case of a Friedmann-Robertson-Walker (FRW) universe.
Abstract: Recently, a Hamilton–Jacobi method beyond the semiclassical approximation in black hole physics was developed by Banerjee and Majhi. We generalize their analysis of black holes to the case of a Friedmann–Robertson–Walker (FRW) universe. It is shown that all the higher order quantum corrections in the single particle action are proportional to the usual semiclassical contribution. The corrections to the Hawking-like temperature and entropy of the apparent horizon for the FRW universe are also obtained. In the corrected entropy, the area law involves a logarithmic area correction together with the standard term with the inverse power of the area.
TL;DR: In this paper, a numerical approach is considered for spherically symmetric spacetimes that generalize Lema\^{\i}tre\char21{}Tolman\char 21{}Bondi dust solutions to nonzero pressure.
Abstract: A numerical approach is considered for spherically symmetric spacetimes that generalize Lema\^{\i}tre\char21{}Tolman\char21{}Bondi dust solutions to nonzero pressure (``LTB spacetimes''). We introduce quasilocal (QL) variables that are covariant LTB objects satisfying evolution equations of Friedman\char21{}Lema\^{\i}tre\char21{}Robertson\char21{}Walker (FLRW) cosmologies. We prove rigorously that relative deviations of the local covariant scalars from the QL scalars are nonlinear, gauge invariant and covariant perturbations on a FLRW formal background given by the QL scalars. The dynamics of LTB spacetimes is completely determined by the QL scalars and these exact perturbations. Since LTB spacetimes are compatible with a wide variety of ``equations of state,'' either single fluids or mixtures, a large number of known solutions with dark matter and dark energy sources in a FLRW framework (or with linear perturbations) can be readily examined under idealized but nontrivial inhomogeneous conditions. Coordinate choices and initial conditions are derived for a numerical treatment of the perturbation equations, allowing us to study nonlinear effects in a variety of phenomena, such as gravitational collapse, nonlocal effects, void formation, dark matter and dark energy couplings, and particle creation. In particular, the embedding of inhomogeneous regions can be performed by a smooth matching with a suitable FLRW solution, thus generalizing the Newtonian ``top hat'' models that are widely used in astrophysical literature. As examples of the application of the formalism, we examine numerically the formation of a black hole in an expanding Chaplygin gas FLRW universe, as well as the evolution of density clumps and voids in an interactive mixture of cold dark matter and dark energy.
TL;DR: In this paper, noncommutative Einstein equations for abelian twists and their solutions in consistently symmetry reduced sectors, corresponding to twisted FRW cosmology and Schwarzschild black holes are derived.
Abstract: We derive noncommutative Einstein equations for abelian twists and their solutions in consistently symmetry reduced sectors, corresponding to twisted FRW cosmology and Schwarzschild black holes. While some of these solutions must be rejected as models for physical spacetimes because they contradict observations, we find also solutions that can be made compatible with low energy phenomenology, while exhibiting strong noncommutativity at very short distances and early times.
Posted Content•
14 Sep 2009
TL;DR: In this paper, the authors investigated the validity of the generalized second law of gravitational thermodynamics in a non-flat FRW universe containing the interacting new agegraphic dark energy with cold dark matter.
Abstract: We investigate the validity of the generalized second law of gravitational thermodynamics in a non-flat FRW universe containing the interacting new agegraphic dark energy with cold dark matter. The boundary of the universe is assumed to be enclosed by the dynamical apparent horizon. We show that for this model, the equation of state parameter can cross the phantom divide. We also present that for the selected model under thermal equilibrium with the Hawking radiation, the generalized second law is always satisfied throughout the history of the universe. Whereas, the evolution of the entropy of the universe and apparent horizon, separately, depends on the equation of state parameter of the interacting new agegraphic dark energy model.
TL;DR: In this paper, a complete classification of dynamical intersecting brane solutions with/without M-waves and Kaluza-Klein monopoles in eleven-dimensional supergravity is presented.
Abstract: We present dynamical intersecting brane solutions in higher-dimensional gravitational theory coupled to dilaton and several forms. Assuming the forms of metric, form fields, and dilaton field, we give a complete classification of dynamical intersecting brane solutions with/without M-waves and Kaluza-Klein monopoles in eleven-dimensional supergravity. We apply these solutions to cosmology and black holes. It is shown that these give FRW cosmological solutions and in some cases Lorentz invariance is broken in our world. If we regard the bulk space as our universe, we may interpret them as black holes in the expanding universe. We also discuss lower-dimensional effective theories and point out naive effective theories may give us some solutions which are inconsistent with the higher-dimensional Einstein equations.
TL;DR: In this article, a spherically symmetric perturbation of a dust dominated Ω = 1 FRW universe in the Newtonian gauge can lead to an apparent acceleration of standard candles and provide a fit to the magnitude-redshift relation inferred from the supernovae data.
Abstract: We show that a spherically symmetric perturbation of a dust dominated Ω = 1 FRW universe in the Newtonian gauge can lead to an apparent acceleration of standard candles and provide a fit to the magnitude-redshift relation inferred from the supernovae data, while the perturbation in the gravitational potential remains small at all scales. We also demonstrate that the supernovae data does not necessarily imply the presence of some additional non-perturbative contribution by showing that any Lemaitre-Tolman-Bondi model fitting the supernovae data (with appropriate initial conditions) will be equivalent to a perturbed FRW spacetime along the past light cone.
TL;DR: In this article, the cosmological horizon of a certain class of Friedmann-Robertson-Walker (FRW) spacetimes has been studied in the context of quantum field theory.
Abstract: As a starting point, we state some relevant geometrical properties enjoyed by the cosmological horizon of a certain class of Friedmann-Robertson-Walker backgrounds. Those properties are generalised to a larger class of expanding spacetimes M admitting a geodesically complete cosmological horizon \({{\Im^-}}\) common to all co-moving observers. This structure is later exploited in order to recast, in a cosmological background, some recent results for a linear scalar quantum field theory in spacetimes asymptotically flat at null infinity. Under suitable hypotheses on M, encompassing both the cosmological de Sitter background and a large class of other FRW spacetimes, the algebra of observables for a Klein-Gordon field is mapped into a subalgebra of the algebra of observables \({{\mathcal{W}(\Im^-)}}\) constructed on the cosmological horizon. There is exactly one pure quasifree state λ on \({{\mathcal{W}(\Im^-)}}\) which fulfills a suitable energy-positivity condition with respect to a generator related with the cosmological time displacements. Furthermore λ induces a preferred physically meaningful quantum state λM for the quantum theory in the bulk. If M admits a timelike Killing generator preserving \({{\Im^-}}\) , then the associated self-adjoint generator in the GNS representation of λM has positive spectrum (i.e., energy). Moreover λM turns out to be invariant under every symmetry of the bulk metric which preserves the cosmological horizon. In the case of an expanding de Sitter spacetime, λM coincides with the Euclidean (Bunch-Davies) vacuum state, hence being Hadamard in this case. Remarks on the validity of the Hadamard property for λM in more general spacetimes are presented.
TL;DR: In this article, the authors study the thermodynamic quantities of Friedmann-Robertson-Walker (FRW) universe by using the tunneling formalism beyond semiclassical approximation developed by Banerjee and Majhi.
Abstract: In this paper, we study the thermodynamic quantities of Friedmann-Robertson-Walker (FRW) universe by using the tunneling formalism beyond semiclassical approximation developed by Banerjee and Majhi [25]. For this we first calculate the corrected Hawking-like temperature on apparent horizon by considering both scalar particle and fermion tunneling. With this corrected Hawking-like temperature, the explicit expressions of the corrected entropy of apparent horizon for various gravity theories including Einstein gravity, Gauss-Bonnet gravity, Lovelock gravity, f(R) gravity and scalar-tensor gravity, are computed. Our results show that the corrected entropy formula for different gravity theories can be written into a general expression (4.39) of a same form. It is also shown that this expression is also valid for black holes. This might imply that the expression for the corrected entropy derived from tunneling method is independent of gravity theory, spacetime and dimension of the spacetime. Moreover, it is concluded that the basic thermodynamical property that the corrected entropy on apparent horizon is a state function is satisfied by the FRW universe.
TL;DR: In this paper, the authors investigated the dynamics of a flat FRW cosmological model with a non-minimally coupled scalar field with the coupling term ξRψ2 in the action.
Abstract: In this publication we investigate dynamics of a flat FRW cosmological model with a non-minimally coupled scalar field with the coupling term ξRψ2 in the scalar field action. The quadratic potential function V(ψ) ∝ ψ2 is assumed. All the evolutional paths are visualized and classified in the phase plane, at which the parameter of non-minimal coupling ξ plays the role of a control parameter. The fragility of global dynamics with respect to changes of the coupling constant is studied in details. We find that the future big rip singularity appearing in the phantom scalar field cosmological models can be avoided due to non-minimal coupling constant effects. We have shown the existence of a finite scale factor singular point (future or past) where the Hubble function as well as its first cosmological time derivative diverge.
TL;DR: Cai et al. as discussed by the authors obtained the Hawking temperature associated with the apparent horizon, which was extensively applied in investigating the relationship between the first law of thermodynamics and Friedmann equations.
TL;DR: In this article, the cosmological constant problem is studied in a two component model with an inhomogeneous equation of state, and it is shown that, in a proper parameter regime, the expansion of the universe with a large absolute value of the Cosmological Constant may asymptotically tend to de Sitter space corresponding to a small effective positive cosmology constant.
TL;DR: In this article, the Born-Infeld deformation strategy to smooth theories having divergent solutions is applied to the teleparallel equivalent of General Relativity, and a deformed theory of gravity based on second order differential equations is built just from first derivatives of the vierbein.
Abstract: Born-Infeld deformation strategy to smooth theories having divergent solutions is applied to the teleparallel equivalent of General Relativity. The equivalence between teleparallelism and General Relativity is exploited to obtain a deformed theory of gravity based on second order differential equations, since teleparallel Lagrangian is built just from first derivatives of the vierbein. We show that Born-Infeld teleparallelism cures the initial singularity in a spatially flat FRW universe; moreover, it provides a natural inflationary stage without resorting to an inflaton field. The Born-Infeld parameter λ bounds the dynamics of Hubble parameter H(t) and establishes a maximum attainable spacetime curvature.
TL;DR: In this paper, a cosmological model of the FRW universe with variable $G$ and $\Lambda$ was considered and the solutions have been obtained for flat model with particular form of cosmology constant.
Abstract: We have considered a cosmological model of the FRW universe with variable $G$ and $\Lambda$. The solutions have been obtained for flat model with particular form of cosmological constant. The cosmological parameters have also been obtained for dust, radiation and stiff matter. The statefinder parameters are analyzed and have shown that these depends only on $w$ and $\epsilon$. Further the lookback time, proper distance, luminosity distance and angular diameter distance have also been calculated for our model.
TL;DR: In this paper, noncommutative Einstein equations for abelian twists and their solutions in consistently symmetry reduced sectors, corresponding to twisted FRW cosmology and Schwarzschild black holes are derived.
Abstract: We derive noncommutative Einstein equations for abelian twists and their solutions in consistently symmetry reduced sectors, corresponding to twisted FRW cosmology and Schwarzschild black holes. While some of these solutions must be rejected as models for physical spacetimes because they contradict observations, we find also solutions that can be made compatible with low energy phenomenology, while exhibiting strong noncommutativity at very short distances and early times.
TL;DR: In this article, the fermion propagator in Friedmann-Lemaˆitre-Robertson-Walker (FLRW) spacetimes with constant deceleration q = −1, = −H˙ /H2 for excited states was calculated.
Abstract: We calculate the fermion propagator in Friedmann–Lemaˆitre–Robertson– Walker (FLRW) spacetimeswith constant deceleration q = −1, = −H˙ /H2 for excited states. For fermions whose mass is generated by a scalar field through a Yukawa coupling m = gYφ, we assume φ ∝α H. We first solve the mode functions by splitting the spinor into a direct product of helicity and chirality spinors. We also allow for non-vacuum states. We normalize the spinors using a consistent canonical quantization and by requiring orthogonality of particle and anti-particle spinors. We apply our propagator to calculate the one-loop effective action and renormalize using dimensional regularization. Since the Hubble parameter is now treated dynamically, this paves the way to study the dynamical backreaction of fermions on the background spacetime.
TL;DR: In this article, the authors present transformations required to recast the Robertson-Walker metric and Friedmann-Robertson-Walker equations in terms of observer-dependent coordinates for several commonly assumed cosmologies.
Abstract: We present here the transformations required to recast the Robertson-Walker metric and Friedmann-Robertson-Walker equations in terms of observer-dependent coordinates for several commonly assumed cosmologies. The overriding motivation is the derivation of explicit expressions for the radius R_h of our cosmic horizon in terms of measurable quantities for each of the cases we consider. We show that the cosmological time dt diverges for any finite interval ds associated with a process at R -> R_h, which therefore represents a physical limit to our observations. This is a key component required for a complete interpretation of the data, particularly as they pertain to the nature of dark energy. With these results, we affirm the conclusion drawn in our earlier work that the identification of dark energy as a cosmological constant does not appear to be consistent with the data.
Posted Content•
10 Jul 2009
TL;DR: In this article, the spin-0 scalar mode of the graviton has been studied in both the infrared and ultraviolet regimes, and it has been shown to be stable in the infrared regime for a factor of 2/3.
Abstract: In the Horava-Lifshitz theory of quantum gravity, two conditions -- detailed balance and projectability -- are usually assumed. The breaking of projectability simplifies the theory, but it leads to serious problems with the theory. The breaking of detailed balance leads to a more complicated form of the theory, but it appears to resolve some of the problems. Sotiriou, Visser and Weinfurtner formulated the most general theory of Horava-Lifshitz type without detailed balance. We compute the linear scalar perturbations of the FRW model in this form of HL theory. We show that the higher-order curvature terms in the action lead to a gravitational effective anisotropic stress on small scales. Specializing to a Minkowski background, we study the spin-0 scalar mode of the graviton, using a gauge-invariant analysis, and find that it is stable in both the infrared and ultraviolet regimes for $0 \le \xi \le 2/3$. However, in this parameter range the scalar mode is a ghost.
TL;DR: In this article, the authors discuss the thermodynamic properties of the Friedmann-Robertson-Walker universe with dark energy fluids labelled by ω = p / ρ − 1 / 3.
TL;DR: In this article, the authors investigated the light propagation by means of the Robertson-McVittie solution which is considered to be the spacetime around the gravitating body embedded in the FLRW (Friedmann-Lemaitre-Robertson-Walker) background metric.
TL;DR: In this paper, the dynamics of the FLRW flat cosmological models in which the vacuum energy density varies with time were studied. And the authors investigated the dynamical properties of a generalized vacuum model, and found that under certain circumstances the vacuum term in the radiation era varies as Λ(z) ∝ (1 + + + ) 4, while in the matter era it has a constant energy density up to z = 3.
Abstract: We study the dynamics of the FLRW flat cosmological models in which the vacuum energy density varies with time, Λ(t) In particular, we investigate the dynamical properties of a generalized vacuum model, and we find that under certain circumstances the vacuum term in the radiation era varies as Λ(z) ∝ (1 + + ) 4 , while in the matter era we have Λ(z) ∝ (1 + z) 3 up to z = 3 and Λ(z) ≃ Λ for z ≤ 3 The confirmation of such a behavior would be of paramount importance because it could provide a solution to the cosmic coincidence problem as well as to the fine-tuning problem, without changing the well known (from the concordance Λ-cosmology) Hubble expansion