Anisotropic Bianchi type-I models in string cosmology

Abstract

The present study deals with a spatially homogeneous and anisotropic Bianchi-I cosmological models representing massive strings. The energy-momentum tensor, as formulated by Letelier (1983), has been used to construct massive string cosmological models for which we assume the expansion scalar in the models is proportional to one of the components of shear tensor. The Einstein's field equations have been solved by applying a variation law for generalized Hubble's parameter in Bianchi-I space-time. We have analysed a comparative study of accelerating and decelerating models in the presence of string scenario. The study reveals that massive strings dominate in the decelerating universe whereas strings dominate in the accelerating universe. The strings eventually disappear from the universe for sufficiently large times, which is in agreement with current astronomical observations.

Anisotropic Bianchi Type-I String Cosmological Models in Normal Gauge for Lyra’s Manifold with Constant Deceleration Parameter

“…Motivated by the above discussions, in this paper, the field equations in normal gauge for Lyra's manifold where gauge function β is taken as time dependent, have been solved for massive string in presence of perfect fluid distribution of matter by applying a variation law for generalized Hubble's parameter in B-I space-time. The present paper generalizes the recent work of Pradhan and Chouhan [78]. The paper has the following structure.…”

“…Since all the kinematic parameters i.e. the expansion H i in the direction of x, y and z, the Hubble parameter H , expansion scalar θ , shear σ , spatial volume (V ) and anisotropy parameter (Ā) are the same as obtained by Pradhan and Chouhan [78], so we do not report here. If we set β(t) = 0 in our solutions, we get the solutions obtained by Pradhan and Chouhan [78].…”

“…the scalar of expansion (θ ), shear scalar (σ ), the spatial volume V , the average anisotropy parameterĀ and deceleration parameter q for the model (40) are the same as obtained by Pradhan and Chouhan [78], so we do not report their values here. The derived model in this subsection is non-singular.…”

“…The derived model in this subsection is non-singular. If we set β(t) = 0 in our solutions, we get the solutions obtained by Pradhan and Chouhan [78]. …”

Lyra’s Cosmology of Massive Strings in Anisotropic Bianchi-II Space-Time

“…Such type of relations have already been considered by Berman and Gomide [39] for solving FRW models. Later on, many authors (see Kumar and Singh [40], Pradhan et al [41], Yadav [42] and references therein) have studied Bianchi type models by using the special law for Hubble's parameter that yields constant value of deceleration parameter. Considering (ABC) 1 3 as the average scale factor of the anisotropic Bianchi-II space-time, the average Hubble's parameter may be written as…”