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Deceleration parameter
About: Deceleration parameter is a research topic. Over the lifetime, 1776 publications have been published within this topic receiving 89440 citations.
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TL;DR: In this article, a redshift-magnitude relation for the two exact non-uniform pressure spherically symmetric Stephani universes is presented, where the Kristian-Sachs method expanding the relativistic quantities in series is used, but only first order terms in redshift $z$ are considered.
Abstract: A redshift-magnitude relation for the two exact non-uniform pressure spherically symmetric Stephani universes is presented. The Kristian-Sachs method expanding the relativistic quantities in series is used, but only first order terms in redshift $z$ are considered. The numerical results are given both for centrally placed and non-centrally placed observers. In the former case the redshift-magnitude relation does not depend on the direction in the sky and the Friedman limit can be easily performed. It appears that the effect of spatial dependence of pressure is similar to the effect of the deceleration parameter in Friedman models. In the latter case the angular dependence of the relation is important. This may serve as another possible explanation of the non-compatibility of the theoretical curve of the redshift-magnitude relation with observations for large redshift objects in the Friedman universe. On the other hand, comparing the magnitudes of equal redshifts objects in different directions in the sky, one can test the reliability of these models.
27 citations
TL;DR: In this paper, the authors derived two laws of variation of the average scale factor with cosmic time, one is of power-law type and the other is of exponential form, which yields constant value of the deceleration parameter.
Abstract: In this paper we discuss the variation law for Hubble’s parameter with average scale factor in a spatially homogeneous and anisotropic Bianchi type-V space-time model, which yields constant value of the deceleration parameter. We derive two laws of variation of the average scale factor with cosmic time, one is of power-law type and the other is of exponential form. Exact solutions of Einstein field equations with perfect fluid and heat conduction are obtained for Bianchi type-V space-time in these two types of cosmologies. In the cosmology with the power-law, the solutions correspond to a cosmological model which starts expanding from the singular state with positive deceleration parameter. In the case of exponential cosmology, we present an accelerating non-singular model of the Universe. We find that the constant value of deceleration parameter is reasonable for the present day Universe and gives an appropriate description of evolution of Universe. We have also discussed different types of physical and kinematical behaviour of the models in these two types of cosmologies.
27 citations
TL;DR: In this article, a spatially homogeneous and isotropic FRW space-time with perfect fluid and dark energy components is considered, where the two sources are assumed to interact minimally, and therefore their energy momentum tensors are conserved separately.
Abstract: The paper deals with a spatially homogeneous and isotropic FRW space-time filled with perfect fluid and dark energy components. The two sources are assumed to interact minimally, and therefore their energy momentum tensors are conserved separately. A special law of variation for the Hubble parameter proposed by Berman (Nuovo Cimento B 74:182, 1983) has been utilized to solve the field equations. The Berman’s law yields two explicit forms of the scale factor governing the FRW space-time and constant values of deceleration parameter. The role of dark energy with variable equation of state parameter has been studied in detail in the evolution of FRW universe. It has been found that dark energy dominates the universe at the present epoch, which is consistent with the observations. The physical behavior of the universe has been discussed in detail.
27 citations
TL;DR: In this paper, the behavior of the accelerating universe is investigated for three purely kinetic k-essence models and the equation of state parameter and deceleration parameter for these models is explored.
Abstract: Generalized teleparallel gravity has been suggested to explain the present cosmic acceleration of the Universe. In this paper, we take a spatially homogeneous and anisotropic Bianchi type I Universe in the framework of F(T) gravity. The behavior of the accelerating Universe is investigated for three purely kinetic k-essence models. We explore the equation of state parameter and deceleration parameter for these k-essence models. It is found that all these models exhibit quintessence behavior of the Universe.
27 citations
TL;DR: In this paper, the dynamical aspects of some accelerating models are investigated in the framework of an extension of symmetric teleparallel gravity dubbed as f(Q, T) gravity.
Abstract: The dynamical aspects of some accelerating models are investigated in the framework of an extension of symmetric teleparallel gravity dubbed as f(Q, T) gravity. In this gravity theory, the usual Ricci tensor in the geometrical action is replaced by a functional f(Q, T) where Q is the non-metricity and T is the trace of the energy-momentum tensor. Two different functional forms are considered in the present work. In order to model the Universe, we have considered a signature flipping deceleration parameter simulated by a hybrid scale factor (HSF). The dynamical parameters of the model are derived and analysed. We discuss the role of the parameter space in getting viable cosmological models. It is found that, the models may be useful as suitable geometrical alternatives to the usual dark energy approach.
27 citations