BULK VISCOUS COSMOLOGY

The full causal Muller-Israel-Stewart (MIS) theory of dissipative proc esses in relativistic fluids is applied to a flat, homogeneous, and is otropic universe with bulk viscosity. It is clarified in which sense t he so-called truncated version is a reasonable limiting case of the fu ll theory. The possibility of bulk viscosity-driven inflationary solut ions of the full theory is discussed. As long as the particle number i s conserved, almost all these solutions exhibit an exponential increas e of the temperature. Assuming that the bulk viscous pressure of the M IS theory may also be interpreted as an effective description for part icle production processes, the thermodynamical behavior of the Univers e changes considerably. In the latter case, the temperature increases at a lower rate or may remain constant during a hypothetical de Sitter stage, accompanied by a substantial growth of the comoving entropy.