EVOLUTION OF THE DENSITY PARAMETER IN INFLATIONARY COSMOLOGY IN THE PRESENCE OF SHEAR AND BULK VISCOSITY

We study the dynamical evolution of the cosmological density parameter OMEGA in the presence of shear and bulk viscosity (in first order as well as in extended nonequilibrium thermodynamical settings) perturbations, both analytically and numerically. Our results show that overall the main conclusions of Madsen and Ellis within the FLRW framework, namely, that (i) OMEGA rarely takes values close to unity throughout the evolution of the Universe, (ii) OMEGA almost-equal-to 1 is epoch and equation of state dependent, and (iii) the set of initial conditions leading to OMEGA not-equal 1 at any particular epoch is nonzero, remain robust with respect to such perturbations, particularly at late times. There are, however, important detailed changes to the dynamics at early times.