The aim of this paper is to compare the evolution of viscous cosmological models for three different constitutive equations for the viscous pressure $\sigma$, namely: Eckart theory ($\sigma =-\xi {\nabla }_{\mu }{u}^{\mu }$), Maxwell-Cattaneo theory ($\sigma +\tau \dot{\sigma }=-\xi {\nabla }_{\mu }{u}^{\mu }$), and generalized second-order Israel-Stewart theory ($\sigma +\tau \dot{\sigma }=-\xi {\nabla }_{\mu }{u}^{\mu }-\frac{1}{2}\xi \sigma T\rho u^{\mu }{\nabla }_{\mu }\left(\frac{v\tau }{T\xi }\right)$). 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.

• Received 21 December 1992

DOI:https://doi.org/10.1103/PhysRevD.48.1597