Locally rotationally symmetric (LRS) Bianchi type II string dust viscous fluid cosmological models in Lyra geometry

摘要

In the present study, a locally rotationally symmetric Bianchi type II string dust cosmological model with varying bulk viscosity in the framework of Lyra geometry is investigated. To get the deterministic solution, we have assumed that shear (sigma) is proportional to the expansion (theta) and zeta theta = constant, where zeta is the coefficient of bulk viscosity. The ansatz zeta theta = constant, was found to coincide with the occurrence of Little Rip (LR) cosmology using Friedmann-Robertson-Walker metric (Breviket al. Phys. Rev. D, 84, 103508-1-6 (2011)). The model describes the pre-inflationary stage of the universe. The presence of viscosity leads to inflationary-like solutions. Anisotropy is maintained because of the presence of strings. The presence of bulk viscosity prevents the matter density from vanishing. In a special case, the model represents the isotropy of the universe. The universe passes through a decelerating stage to an accelerating phase, which is in agreement with Ries et al.' s (Astrophys. J. 607, 665 (2004). doi: 10.1086/383612) type Ia supernovae astronomical observations. The displacement vector (beta) of Lyra geometry is a decreasing function of time analogous to the cosmological constant (Lambda) of general relativity. We have attempted to explore the possibility of constructing a string dust viscous fluid cosmological model in Bianchi type II space-time with displacement vector (beta) in Lyra geometry using the geometric condition that shear is proportional to expansion.