Statefinder analysis of universe models with a viscous cosmic fluid and   a fluid with a non-linear equation of state
  In the present article we analyze, by means of the statefinder parameter formalism, some universe models introduced by Brevik and co-workers. We determine constants that earlier were left unspecified, in terms of observable quantities. It is verified that a Big Bang universe model with a fluid having a certain non-linear equation of state behaves in the same way as a model with a viscous fluid. 
Oyvind Gron