Particle horizon

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

Cosmological evolution for dark energy models in f(T) gravity

Abstract: In this paper, we investigate the behavior of equa- tion of state parameter and energy density for dark energy in the framework of f( T ) gravity. For this purpose, we use anisotropic LRS Bianchi type I universe model. The be- havior of accelerating universe is discussed for some well- known f( T ) models. It is found that the universe takes a transition between phantom and non-phantom phases for f( T ) models except exponential and logarithmic models. We conclude that our results are relativity analogous to the results of FRW universe.

Back reaction of the neutrino field in an Einstein universe

Abstract: The back-reaction effect of the neutrino field at finite temperature in the background of the static Einstein universe is investigated. A relationship between the temperature of the universe and its radius is found. As in previously studied cases of the massless scalar field and the photon field, this relation exhibits a minimum radius below which no self-consistent solution for the Einstein field equation can be found. A maximum temperature marks the transition from a vacuum-dominated state to the radiation-dominated state universe. In light of the results obtained for the scalar, neutrino and photon fields, the role of the back reaction of quantum fields in controlling the value of the cosmological constant is briefly discussed.

Evolution of density perturbations in a large void universe

Abstract: We study the evolution of linear density perturbations in a large spherical void universe which accounts for the acceleration of the cosmic volume expansion without introducing dark energy. The density contrast of this void is not large within the light cone of an observer at the center of the void. Therefore, we describe the void structure as a perturbation with a dimensionless small parameter $\kappa$ in a homogeneous and isotropic universe within the region observable for the observer. We introduce additional anisotropic perturbations with a dimensionless small parameter $\epsilon$, whose evolution is of interest. Then, we solve perturbation equations up to order $\kappa \epsilon$ by applying second-order perturbation theory in the homogeneous and isotropic universe model. By this method, we can know the evolution of anisotropic perturbations affected by the void structure. We show that the growth rate of the anisotropic density perturbations in the large void universe is significantly different from that in the homogeneous and isotropic universe. This result suggests that the observation of the distribution of galaxies may give a strong constraint on the large void universe model.

A counterexample to claimed COBE constraints on compact toroidal universe models

Abstract: It has been suggested that if the Universe satisfies a flat, multiply connected, perturbed Friedmann-Lemaitre model, then cosmic microwave background data from the COBE satellite implies that the minimum size of the injectivity diameter (shortest closed spatial geodesic) must be larger than about (2/5) of the horizon diameter. To show that this claim is misleading, a simple T2×R universe model of injectivity diameter a quarter of this size, i.e. a tenth of the horizon diameter, is shown to be consistent with COBE four-year observational maps of the cosmic microwave background. This is done using the identified circles principle.