Viscosity effects on the early universe with time-varying constants

We study the effects of bulk viscosity on the early evolution of a flat Friedmann-Roberson-Walker universe, in the presence of variable gravitational and cosmological "constants". The conservation principle is taken into account. In this paper it is showed how to vary the adiabatic parameter gamma of the "gamma law" equation of state-p = (-gamma-1)rho as a function of cosmic time in order to solve Einstein's field equations in a unified manner for two different early phases of universe. A unified description of the early evolution of the universe is presented in which an inflationary phase is followed by a radiation-dominated phase. Allowing the gravitational constant to change with time leads to an ever-increasing function. Within a discussed class of models singular and non-singular solutions are obtained. The introduction of viscosity not only removes singularity but also gives the deceleration parameter a freedom to vary with the scale factor. It has been shown that the cosmological models are consistent with the adoption of a positive cosmological constant.