Viscous cosmological models and accelerated universes

It is shown that a present acceleration with a past deceleration is a possible solution to the Friedmann equation by considering the Universe as a mixture of a scalar with a matter field and by including a nonequilibrium pressure term in the energy-momentum tensor. The dark energy density decays more slowly with respect to the time than the matter energy density does. The inclusion of the nonequilibrium pressure leads to a less pronounced decay of the matter field with a shorter period of past deceleration.