New classes of exact causal viscous cosmologies

Abstract

Two particular exact solutions of the gravitational field equations for a homogeneous flat Friedmann-Robertson-Walker universe filled with a causal bulk viscous fluid in the framework of the full Israel-Stewart-Hiscock theory are presented. The dynamics of the universe is entirely determined in the present models by its thermal behavior. The solutions of the field equations are expressed in an exact closed parametric form and correspond to an inflationary transition between a singular state and a Minkowskian space-time and a quasi-Minkowskian era and an inflationary state, connected by a noninflationary phase, respectively. The inflationary era of the first solution is associated with an increase in temperature and energy density (a heating period), but with a decrease of the comoving entropy. The evolutionary period described by the second solution leads during its noninflationary phase to a rapid decrease in the temperature, the energy density, and the comoving entropy of the corresponding universe.