Abstract
Einstein's field equations with variable gravitational and cosmological "constants" are considered in the presence of perfect fluid for a spatially homogeneous and isotropic universe. Exact solutions of the field equations are obtained by using the "gamma-law" equation of state p=(γ-1)ρ, where the adiabatic parameter γ, varies with cosmic time. The functional form of γ, which is assumed to be the function of scale factor R as proposed by Carvalho, is used to describe the early evolution of universe. A unified description of early universe is given in which an inflationary phase is followed by radiation-dominated phase. The various physical aspects of the models are also discussed.
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