RELATIONSHIP BETWEEN 2 THEORIES OF DISSIPATIVE RELATIVISTIC HYDRODYNAMICS APPLIED TO COSMOLOGY

We compare Israel's relativistic causal theory of transient effects wi th the relativistic extended irreversible thermodynamics of Pavon, Jou , and Casas-Vasquez, applying both to the case of cosmic fluid with bu lk viscosity only. They are completely equivalent up to the first orde r in the parameter characterizing the departure from equilibrium. We s how, if certain relations between the main variables of the two theori es hold, that they are also equivalent up to the second order in this parameter. We also extend up to any order Israel's theory and give the relations permitting again the equivalence between the two theories i n this general case. Some cosmological consequences are discussed.