Abstract
A class of homogeneous and isotropic zero-curvature Robertson-Walker models with bulk viscosity is studied. Solutions are obtained with the parameter gamma of the “γ-law” equation of state p = (γ – 1)ρ in which the adiabatic parameter gamma varies continuously as the universe expands. A unified description of the early evolution of the universe is presented with constant bulk viscosity and time-dependent bulk viscosity in which an inflationary period is followed by a radiation-dominated phase. We also establish the time dependence of the cosmological constant in terms of varying γ index. Some physical properties of the models are also discussed.
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