LRS Bianchi Type II Massive String Cosmological Model for Stiff Fluid Distribution with Decaying Vacuum Energy (Λ)

Abstract

An LRS Bianchi Type II model formed by massive strings with decaying vacuum energy (Λ) for stiff fluid distribution is studied in the context of general relativity. To get the deterministic model, we have assumed that \(\frac{\sigma}{\theta} =\mathrm{constant}\) where σ is shear and θ the expansion in the model and decaying vacuum energy (Λ) is proportional to H2 (H is Hubble parameter) as used in Arbab (Gen. Relativ. Gravit. 29:51, 1997). We find that the model represents decelerating and accelerating phases of universe. The decaying vacuum energy (Λ) is proportional to \(\frac{1}{\tau^{2}}\) as obtained by Bertolami (Nuovo Cimento B 93:36, 1986) and Hubble parameter is proportional to \(\frac{1}{\tau}\) which matches with the observation. The model in general represents anisotropic space-time. However, in special case, it isotropizes. The particle density (ρp) and string tenson (λ) are initially large but decrease due to lapse of time. The model also admits particle horizon and entropy is inversely proportional absolute temperature. Thus the model is in good agreement with present age of universe.