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

Abstract

The present study reexamines the recent work of Pradhan et al. (Indian J. Phys. 88: 757, 2014) and obtained general exact solutions of the Einstein's field equations with variable gravitational and cosmological "constants" for a spatially homogeneous and anisotropic Bianchi type-I space-time. To study the transit behaviour of Universe, we consider a law of variation of scale factor a(t) = t k e t 1 n which yields a time dependent deceleration parameter q = −1 + 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 give 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 ≥ 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 tend 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 (Farooq and Ratra, Astrophys. J. 66: L7, 2013). Some physical and geometric properties of the models are also discussed.

A Study of Transition of the Expansion of the Universe from a Phase of Deceleration to Acceleration through a Conversion of Matter into Dark Energy in the Framework of Brans-Dicke Theory

“…The gravitational constant is found to increase with time with a varying rate. This increasing nature of , with time, has been found in many other studies [28,29,30,32,35].…”

“…One easily obtains the time dependence of gravitational constant from the time dependence of . An important finding of this study is that the gravitational constant gradually increases with time, as evident from many other studies not based on Brans-Dicke theory [35]. On the basis of our results we have graphically depicted the time variation of a quantity 3 which can be regarded as a measure of the matter content of the universe.…”

Cosmic acceleration and varying alpha in anisotropic universe

“…Utilising physical conditions for spatially homogeneous metric such as taking expansion scalar proportional to shear scalar make it easier to tackle these equations (Collins et al 1980). Alternatively, by using the techniques in Saha (2005), the authors in Yadav and Saha (2012), Sepehri et al (2014), Pradhan et al (2014), Amirhashchi and Pradhan (2014) and Mishra et al (2013) have simplified the system of equations and solved them analytically. Here, in a different approach, we reduce the second order coupled non linear differential equations into compact and neat first order ones by introducing the following new variables as (Farajollahi et al 2011a(Farajollahi et al , 2011b(Farajollahi et al , 2012a(Farajollahi et al , 2012b,…”

Could the Lyra manifold be the hidden source of the dark energy?

“…Recently, Priyokumar and Mollah [61] studied about higher dimensional LRS Bianchi type-I cosmological model universe interacting with perfect fluid in Lyra geometry with different cases. Many authors [62][63][64][65][66][67][68][69][70] have studied Bianchi type models in order to examine the role of certain anisotropic sources during the formation of the large-scale structures that we see in the present universe and for better understanding the small amount of observed anisotropy in the universe. Banerjee et al, [71] have investigated Bianchi type-I cosmological models with viscous fluid in higher dimensional space time.…”