Nonequilibrium relativistic thermodynamics in bulk viscous cosmology - art. no. 023510

Three different approaches to the relativistic thermodynamics of imperfect fluids are compared: the second-order causal theory of Israel and Stewart ( IS), the phenomenological extension of the IS theory proposed by Maartens a nd Mendez (MM), and the recently developed GENERIC formalism of Crmela and Ottinger. All theories are applied to the case of dissipative cosmology, wi th bulk viscosity as the only dissipative phenomenon. The MM theory as well as GENERIC give an upper bound on the bulk viscous stress, whereas there i s none in the IS theory. In a flat Robertson-Walker universe, the relations hip between the different approaches is illustrated for the special case of a relativistic Boltzmann gas. Far away from equilibrium we find qualitativ ely different behavior, indicating that care should be taken when using the IS theory in this regime.