Deceleration parameter

About: Deceleration parameter is a research topic. Over the lifetime, 1776 publications have been published within this topic receiving 89440 citations.

Kaluza-Klein cosmological model in $f(R,T)$ gravity with $\Lambda(T)$

Abstract: A class of Kaluza-Klein cosmological models in $f(R,T)$ theory of gravity have been investigated. In the work, we have considered the functional $f(R,T)$ to be in the form $f(R,T)=f(R)+f(T)$ with $f(R)=\lambda R$ and $f(T)=\lambda T$. Such a choice of the functional $f(R,T)$ leads to an evolving effective cosmological constant $\Lambda$ which depends on the stress energy tensor. The source of the matter field is taken to be a perfect cosmic fluid. The exact solutions of the field equations are obtained by considering a constant deceleration parameter which leads two different aspects of the volumetric expansion namely a power law and an exponential volumetric expansion. Keeping an eye on the accelerating nature of the universe in the present epoch, the dynamics and physical behaviour of the models have been discussed. From statefinder diagnostic pair we found that the model with exponential volumetric expansion behaves more like a $\Lambda$CDM model.

Bianchi type-I transit cosmological models with time dependent gravitational and cosmological constants: reexamined

Abstract: The Einstein’s field equations with variable gravitational and cosmological “constants” for a spatially homogeneous and anisotropic Bianchi type-I space-time are obtained in present study. To study the transit behaviour of Universe, we consider a law of variation of scale factor $$a(t) = \left( t^{k} e^{t}\right) ^{\frac{1}{n}}$$ , which yields a time dependent deceleration parameter $$q = -1 + \frac{nk}{(k + t)^{2}}$$ , comprising a class of models that depicts a transition of the universe from the early decelerated phase to the recent accelerating phase. We find that the time dependent deceleration parameter is reasonable for the present day Universe and gives an appropriate description of the evolution of the universe. For $$n = 0.27k$$ , we obtain $$q_{0} = -0.73$$ , which is similar to observed value of deceleration parameter at present epoch. It is also observed that for $$n \ge 2$$ and k = 1, we obtain a class of transit models of the universe from early decelerating to present accelerating phase. For k = 0, the universe has non-singular origin. In these models, we arrive at the decision that, from the structure of the field equations, the behaviour of cosmological and gravitational constants and are related. Taking into consideration the observational data, we conclude that the cosmological constant behaves as a positive decreasing function of time, whereas gravitational constant is increasing and tends to a constant value at late time. $$H(z)/(1+z)$$ data (32 points) and model prediction as a function of redshift for different k and n are successfully presented by using recent data. Some physical and geometric properties of the models are also discussed.

Magnetized strange quark model with Big Rip singularity in $f(R,T)$ gravity

Abstract: LRS (Locally Rotationally symmetric) Bianchi type-I magnetized strange quark matter cosmological model have been studied based on $f(R,T)$ gravity. The exact solutions of the field equations are derived with linearly time varying deceleration parameter which is consistent with observational data (from SNIa, BAO and CMB) of standard cosmology. It is observed that the model start with big bang and ends with a Big Rip. The transition of deceleration parameter from decelerating phase to accelerating phase with respect to redshift obtained in our model fits with the recent observational data obtained by Farook et al. in 2017. The well known Hubble parameter $H(z)$ and distance modulus $\mu(z)$ are discussed with redshift.