Exact solution of perfect fluid massive string cosmology in Bianchi type III space-time with decaying vacuum energy density Λ

Exact solution of Einstein's field equations is obtained for massive string cosmological model of Bianchi III space-time using the technique given by Letelier (Phys. Rev. D 20:2414, 1983) in presence of perfect fluid and decaying vacuum energy density Lambda. To get the deterministic solution of the field equations the expansion theta in the model is considered as proportional to the eigen value sigma(2)(2) of the shear tensor sigma(i)(i) and also the fluid obeys the barotropic equation of state. The vacuum energy density Lambda is found to be positive and a decreasing function of time which is supported by the results from recent supernovae Ia observations. It is also observed that in early stage of the evolution of the universe string dominates over the particle whereas the universe is dominated by massive string at the late time. Some physical and geometric properties of the model are also discussed.