Equations of state and transport equations in viscous cosmological models

The aim of this paper is to compare the evolution of viscous cosmological models for three different constitutive equations for the viscous pressure σ, namely: Eckart theory (σ=-ξμuμ), Maxwell-Cattaneo theory (σ+τσ=-ξμuμ), and generalized second-order Israel-Stewart theory (σ+τσ=-ξμuμ- 12ξσTρuμμ(vτTξ)). In the last case, the nonlinear terms may be interpreted as a consequence of nonlinear equations of state for absolute temperature and thermodynamic pressure. We show that the nonlinear terms of the latter equation are compatible with a viscosity-driven inflationary expansion. © 1993 The American Physical Society.