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.

Consequences for some dark energy candidates from the type Ia supernova SN 1997ff

Abstract: We examine the status of various dark energy models in light of the recently observed SN 1997ff at z 1.7. The modified data still fit a pure cosmological constant A or a quintessence with an equation of state similar tothat of A. The kinematical A models, Λ ∼ S - 2 and Λ ∼ H 2 , also fit the data reasonably well and require less dark energy density (hence more matter energy density) than is required by the constant A model. However, the model Λ ∼ S - 2 with low energy density becomes unphysical as it cannot accommodate higher redshift objects. We also examine an alternative explanation of the data, namely the absorption by the intervening whisker-like dust, and find that the quasi-steady state (QSS) model and the Friedmann-Robertson-Walker (FRW) model Ω m 0 = 0.33 without any dark energy also fit the data reasonably well. We notice that the addition of SN 1997ff to the old data has worsened the fit to most of the models, except a closed FRW model with a constant A and a closed quintessence model with ω Φ = -0.82, and the models have started departing from each other as we go above z = 1. However, to make a clear discrimination possible, a few more supernovae with z > 1 are required. We have also calculated the age of the Universe in these models and find that, in the models with a constant A, the expansion age is uncomfortably close to the age of the globular clusters. Quintessence models show even lower age. The kinematical A models are, however, interesting in this connection (especially the model A ∼ H 2 ), as they give a remarkably large age of the Universe.

Cosmic acceleration from modified gravity with Palatini formalism

Abstract: We study new FRW type cosmological models of modified gravity treated on the background of Palatini approach. These models are generalization of Einstein gravity by the presence of a scalar field non-minimally coupled to the curvature. The models employ Starobinsky's term in the Lagrangian and dust matter. Therefore, as a by-product, an exhausted cosmological analysis of general relativity amended by quadratic term is presented. We investigate dynamics of our models, confront them with the currently available astrophysical data as well as against ΛCDM model. We have used the dynamical system methods in order to investigate dynamics of the models. It reveals the presence of a final sudden singularity. Fitting free parameters we have demonstrated by statistical analysis that this class of models is in a very good agreement with the data (including CMB measurements) as well as with the standard ΛCDM model predictions. One has to use statefinder diagnostic in order to discriminate among them. Therefore Bayesian methods of model selection have been employed in order to indicate preferred model. Only in the light of CMB data the concordance model remains invincible.

Particle vs. future event horizon in interacting holographic dark energy model

Abstract: By choosing the future event horizon as the horizon of the flat FLRW universe, we show that although the interacting holographic dark energy model is able to explain the phantom divide line crossing, but the thermodynamics second law is not respected in this model. We show that if one takes the particle event horizon as the horizon of the universe, besides describing $\omega=-1$ crossing in a consistent way with thermodynamics second law, he is able to determine appropriately the ratio of dark matter to dark energy density at transition time. In this approach, after the first transition from quintessence to phantom, there is another transition from phantom to quintessence phase which avoids the big rip singularity.

Zero-Curvature Friedmann-Robertson-Walker Models as Exact Viscous Magnetohydrodynamic Cosmologies

Abstract: It is shown that FRW cosmologies, in particular the zero-curvature models,do not necessarily represent perfect fluid solutions but also can be exact solutions of the field equations for a viscous fluid, with or without an electromagnetic field, and that these solutions can be physically acceptable. The viscous, magnetohydrodynamic model with metric identical to that of the perfect fluid model with equation of state p-bar = ..gamma..rho-bar is investigated and particular attention is given to the Einstein-de Sitter model which corresponds to ..gamma.. = 0. The behavior of the expansion of the velocity congruence in the viscous interpretation is quite different from that of the standard model, which suggests that the usual treatment of the critical density problem may be questionable.