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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.
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TL;DR: In this paper, a static Friedmann brane with zero cosmological constant and 3-curvature, but satisfying p > 0 and p + 3p > 0, is shown to have a different relation between the density, pressure, curvature and cosmology constant than in the case of the general relativistic Einstein static universe.
Abstract: A static Friedmann brane in a five-dimensional bulk (Randall-Sundrum-type scenario) can have a very different relation between the density, pressure, curvature and cosmological constant than in the case of the general relativistic Einstein static universe. In particular, static Friedmann branes with zero cosmological constant and 3-curvature, but satisfying p > 0 and p + 3p > 0, are possible. Furthermore, we find static Friedmann branes in a bulk that satisfies the Einstein equations but is not Schwarzschild-anti-de Sitter or its specializations. In the models with negative bulk cosmological constant, a positive brane tension leads to negative density and 3-curvature.
87 citations
TL;DR: In this paper, a new class of physical states of the free Klein-Gordon field in Robertson-Walker spacetimes was constructed by minimizing the expectation value of smeared stress energy.
Abstract: We construct a new class of physical states of the free Klein–Gordon field in Robertson–Walker spacetimes This is done by minimizing the expectation value of smeared stress–energy We get an explicit expression for the state depending on the smearing function We call it a state of low energy States of low energy are an improvement of the concept of adiabatic vacua on Robertson–Walker spacetimes The latter are approximations of the former It is shown that states of low energy are Hadamard states
87 citations
TL;DR: In this article, the authors derived an exact solution of an isotropic and homogeneous universe governed by gravity, and showed that the solution constrains the torsion scalar to be a constant function at all time.
Abstract: In the present work we derive an exact solution of an isotropic and homogeneous Universe governed by $$f(T)$$
gravity. We show how the torsion contribution to the FRW cosmology can provide a unique origin for both early and late acceleration phases of the Universe. The three models (
$$k=0, \pm 1$$
) show a built-in inflationary behavior at some early Universe time; they restore suitable conditions for the hot Big bang nucleosynthesis to begin. Unlike the standard cosmology, we show that even if the Universe initially started with positive or negative sectional curvatures, the curvature density parameter enforces evolution to a flat Universe. The solution constrains the torsion scalar $$T$$
to be a constant function at all time $$t$$
, for the three models. This eliminates the need for dark energy (DE). Moreover, when the continuity equation is assumed for the torsion fluid, we show that the flat and closed Universe models violate the conservation principle, while the open one does not. The evolution of the effective equation of state (EoS) of the torsion fluid implies a peculiar trace from a quintessence-like DE to a phantom-like one crossing a matter and radiation EoS in between; then it asymptotically approaches a de Sitter fate.
87 citations
TL;DR: In this article, it is shown that polymer quantization leads to a modified uncertainty principle similar to that motivated by string theory and non-commutative geometry, which gives a large effect in the early universe.
Abstract: It is shown that polymer quantization leads to a modified uncertainty principle similar to that motivated by string theory and non-commutative geometry. When applied to quantum field theory on general background spacetimes, corrections to the uncertainty principle acquire a metric dependence. For Friedmann–Robertson–Walker cosmology this translates to a scale factor dependence which gives a large effect in the early Universe.
87 citations
TL;DR: In this paper, a consistent, general, and covariant formulation for a single fluid is presented, where the interaction is a natural implication of the imperfectness of the fluids, which makes it difficult to construct a robust formulation of interacting fluids, namely the construction of a Lagrangian whose variation would give rise to the interacting equations.
Abstract: Coupling dark energy and dark matter through an effective fluid description is a very common procedure in cosmology; however, it always remains in comoving coordinates in the special FLRW space. We construct a consistent, general, and covariant formulation, where the interaction is a natural implication of the imperfectness of the fluids. This imperfectness makes difficult the final step towards a robust formulation of interacting fluids, namely the construction of a Lagrangian whose variation would give rise to the interacting equations. Nevertheless, we present a formal solution to this problem for a single fluid, through the introduction of an effective metric.
85 citations