Particle horizon

About: Particle horizon is a research topic. Over the lifetime, 2096 publications have been published within this topic receiving 69137 citations.

Cosmological Constant Dominated Transit Universe from the Early Deceleration Phase to the Current Acceleration Phase in Bianchi-V Spacetime

Abstract: We present the transition of the universe from the early decelerating phase to the current accelerating phase with viscous fluid and time-dependent cosmological constant Λ as a source of matter in Bianchi-V spacetime. To study the transit behaviour of the universe, we assume the scale factor as an increasing function of time, which generates a time-dependent deceleration parameter (DP). The study reveals that the cosmological term does not change its fundamental nature for ξ = const and ξ = ξ(t), where ξ is the coefficient of bulk viscosity. The Λ(t) is found to be positive and is a decreasing function of time. The same behavior was observed during recent supernovae observations. The physical behaviour of the universe is discussed in detail.

Can a dust dominated universe have accelerated expansion

Abstract: Recently, there have been suggestions that the apparent accelerated expansion of the universe is due not to a cosmological constant, but rather to inhomogeneities in the distribution of matter. In this work, we investigate a specific class of inhomogeneous models that can be solved analytically, namely the dust dominated Lemaitre–Tolman–Bondi universe models. We show that they do not permit accelerated cosmic expansion.

CMB observations in LTB universes: Part I: Matching peak positions in the CMB spectrum

Abstract: Acoustic peaks in the spectrum of the cosmic microwave background in spherically symmetric inhomogeneous cosmological models are studied At the photon-baryon decoupling epoch, the universe may be assumed to be dominated by non-relativistic matter, and thus we may treat radiation as a test field in the universe filled with dust which is described by the Lemaitre-Tolman-Bondi (LTB) solution First, we give an LTB model whose distance-redshift relation agrees with that of the concordance $\Lambda$CDM model in the whole redshift domain and which is well approximated by the Einstein-de Sitter universe at and before decoupling We determine the decoupling epoch in this LTB universe by Gamow's criterion and then calculate the positions of acoustic peaks Thus obtained results are not consistent with the WMAP data However, we find that one can fit the peak positions by appropriately modifying the LTB model, namely, by allowing the deviation of the distance-redshift relation from that of the concordance $\Lambda$CDM model at $z>2$ where no observational data are available at present Thus there is still a possibility of explaining the apparent accelerated expansion of the universe by inhomogeneity without resorting to dark energy if we abandon the Copernican principle Even if we do not take this extreme attitude, it also suggests that local, isotropic inhomogeneities around us may seriously affect the determination of the density contents of the universe unless the possible existence of such inhomogeneities is properly taken into account