  With the help of a conformal, timelike Killing-vector we define generalized
equilibrium states for cosmological fluids with particle production. For
massless particles the generalized equilibrium conditions require the
production rate to vanish and the well known ``global'' equilibrium of standard
relativistic thermodynamics is recovered as a limiting case. The equivalence
between the creation rate for particles with nonzero mass and an effective
viscous fluid pressure follows as a consequence of the generalized equilibrium
properties. The implications of this equivalence for the cosmological dynamics
are discussed, including the possibility of a power-law inflationary behaviour.
For a simple gas a microscopic derivation for such kind of equilibrium is given
on the basis of relativistic kinetic theory.

General Relativity and Quantum Cosmology;Astrophysics