Non Existence of Shear in Bianchi Type-III String Cosmological Models with Bulk Viscosity and Time−Dependent Λ Term

We study the non existence of shear in locally rotationally symmetric Bianchi type-III string cosmological models with bulk viscosity and variable cosmological term Λ. Exact solutions of the field equations are obtained by assuming the conditions: the bulk viscosity is proportional to the expansion scalar, ξ∝θ, expansion scalar is proportional to shear scalar, θ∝σ, and Λ is proportional to the Hubble parameter. The coefficient of bulk viscosity is assumed to be a power function of mass density. The corresponding physical interpretations of the cosmological solutions are also discussed.