Topic
Deceleration parameter
About: Deceleration parameter is a research topic. Over the lifetime, 1776 publications have been published within this topic receiving 89440 citations.
Papers published on a yearly basis
Papers
More filters
TL;DR: In this article, the authors investigated the Bianchi type of perfect fluid cosmological models in the modified theory of gravity for a special choice of $f(R,T)=f{1}(R)+f{2}(T)$¯¯¯¯ with $f_{1} (R)=\lambda-1}R$¯¯¯¯ and $f͡(T)= \lambda-2}T$¯¯¯¯.
Abstract: Spatially homogeneous Bianchi type-
$\mathit{II}$
, $\mathit{VIII}$
and $\mathit{IX}$
perfect fluid cosmological models in $f(R,T)$
modified theory of gravity have been investigated for a special choice of $f(R,T)=f_{1}(R)+f_{2}(T)$
with $f_{1}(R)=\lambda_{1}R$
and $f_{2}(T)=\lambda_{2}T$
. This special choice leads to a cosmological constant $\varLambda$
, which depends on stress energy tensor of matter source. To get the deterministic model of Universe, we assume that the expansion scalar (
$\theta$
) in the model is proportional to shear scalar (
$\sigma$
). This condition leads to relation between metric potentials, which yields a time dependent deceleration parameter. Various physical and geometrical features of the models are also discussed.
19 citations
TL;DR: The exact solution of modified EFE (Einstein's field equations) within the scope of spatially homogeneous and isotropic FLRW (Friedmann-Lemaitre-Robertson-Walker) space-time in scalar-tensor BD (Brans-Dicke) theory of gravity is studied in this paper.
Abstract: In this paper we have studied the exact solution of modified EFE (Einstein’s field equations) within the scope of spatially homogeneous and isotropic FLRW (Friedmann-Lemaitre-Robertson-Walker) space-time in scalar-tensor BD (Brans-Dicke) theory of gravity. For the purpose we have proposed DP (Deceleration Parameter) $q$
as a bilinear function of proper cosmic time $t$
as $q = \frac{\alpha (1-t)}{1+t}$
and $q = -\frac{\alpha t}{1+t}$
, here $\alpha $
is a non-negative constant. As per requirement we have already addressed the various aspects of cosmological models. Physical and geometric properties of the models have been also presented.
19 citations
TL;DR: In this paper, the scale dependence of $G$ and $Lambda$ is governed by a set of renormalization group equations which is coupled to Einstein's equation in a consistent way.
Abstract: Cosmologies with a time dependent Newton constant and cosmological constant are investigated. The scale dependence of $G$ and $\Lambda$ is governed by a set of renormalization group equations which is coupled to Einstein's equation in a consistent way. The existence of an infrared attractive renormalization group fixed point is postulated, and the cosmological implications of this assumption are explored. It turns out that in the late Universe the vacuum energy density is automatically adjusted so as to equal precisely the matter energy density, and that the deceleration parameter approaches $q = -1/4$. This scenario might explain the data from recent observations of high redshift type Ia Supernovae and the cosmic microwave background radiation without introducing a quintessence field.
19 citations
TL;DR: In this paper, a spatially homogeneous and anisotropic Bianchi type-I perfect fluid model with variable cosmological constant is considered, and the solutions are consistent with the recent observations of type Ia supernovae.
Abstract: A spatially homogeneous and anisotropic Bianchi type-I perfect fluid model is considered with variable cosmological constant. Einstein’s field equations are solved by using a law of variation for mean Hubble’s parameter, which is related to average scale factor and that yields a constant value of deceleration parameter. An exact and singular Bianchi-I model is presented, where the cosmological constant remains positive and decreases with the cosmic time. It is found that the solutions are consistent with the recent observations of type Ia supernovae. A detailed study of physical and kinematical properties of the model is carried out.
19 citations
TL;DR: In this article, the effect of time dependent bulk viscosity on the evolution of Friedmann models with zero curvature in Brans-Dicke theory is studied and the physical properties of cosmological solutions are also discussed.
Abstract: The effect of time dependent bulk viscosity on the evolution of Friedmann models with zero curvature in Brans-Dicke theory is studied. The solutions of the field equations with ‘gamma-law’ equation of state p = (γ-1) ρ, where γ varies continuously as the Universe expands, are obtained by using the power-law relation φ = bRn, which lead to models with constant deceleration parameter. We obtain solutions for the inflationary period and radiation dominated era of the universe. The physical properties of cosmological solutions are also discussed.
19 citations