Friedmann–Lemaître–Robertson–Walker metric

About: Friedmann–Lemaître–Robertson–Walker metric is a research topic. Over the lifetime, 4113 publications have been published within this topic receiving 87752 citations. The topic is also known as: FLRW metric.

Can the acceleration of our universe be explained by the effects of inhomogeneities

Abstract: No, it is simply not plausible that cosmic acceleration could arise within the context of general relativity from a back-reaction effect of inhomogeneities in our universe, without the presence of a cosmological constant or 'dark energy'. We point out that our universe appears to be described very accurately on all scales by a Newtonianly perturbed FLRW metric. (This assertion is entirely consistent with the fact that we commonly encounter δρ/ρ > 1030.) If the universe is accurately described by a Newtonianly perturbed FLRW metric, then the back-reaction of inhomogeneities on the dynamics of the universe is negligible. If not, then it is the burden of an alternative model to account for the observed properties of our universe. We emphasize with concrete examples that it is not adequate to attempt to justify a model by merely showing that some spatially averaged quantities behave the same way as in FLRW models with acceleration. A quantity representing the 'scale factor' may 'accelerate' without there being any physically observable consequences of this acceleration. It also is not adequate to calculate the second-order stress–energy tensor and show that it has a form similar to that of a cosmological constant of the appropriate magnitude. The second-order stress–energy tensor is gauge dependent, and if it were large, contributions of higher perturbative order could not be neglected. We attempt to clear up the apparent confusion between the second-order stress–energy tensor arising in perturbation theory and the 'effective stress–energy tensor' arising in the 'shortwave approximation'.

Isotropization of arbitrary cosmological expansion given an effective cosmological constant

Abstract: It is shown that given an effective cosmological constant it is possible to construct the asymptotic structure of inhomogeneous cosmological expansion. This structure would contain the maximum possible number of arbitrary functions of three coordinates and would describe exponentially rapid local isotropization of the universe.

Lovelock gravitational field equations in cosmology.

Abstract: We present a systematic study of cosmological solutions in the Lovelock theory of gravitation, including maximally symmetric space-times, Robertson-Walker universes, and product manifolds of symmetric subspaces.

Open FRW universes and self-acceleration from nonlinear massive gravity

Abstract: In the context of a recently proposed nonlinear massive gravity with Lorentz-invariant mass terms, we investigate open Friedmann-Robertson-Walker (FRW) universes driven by arbitrary matter source. While the flat FRW solutions were recently shown to be absent, the proof does not extend to the open universes. We find three independent branches of solutions to the equations of motion for the Stuckelberg scalars. One of the branches does not allow any nontrivial FRW cosmologies, as in the previous no-go result. On the other hand, both of the other two branches allow general open FRW universes governed by the Friedmann equation with the matter source, the standard curvature term and an effective cosmological constant Λ± = c±mg2. Here, mg is the graviton mass, + and - represent the two branches, and c± are constants determined by the two dimensionless parameters of the theory. Since an open FRW universe with a sufficiently small curvature constant can approximate a flat FRW universe but there is no exactly flat FRW solution, the theory exhibits a discontinuity at the flat FRW limit.

The Black Hole and Cosmological Solutions in IR modified Horava Gravity

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