Bulk Viscous Matter-dominated Universes: Asymptotic Properties
  By means of a combined use of the type Ia supernovae and H(z) data tests,
together with the study of the asymptotic properties in the equivalent phase
space - through the use of the dynamical systems tools - we demonstrate that
the bulk viscous matter-dominated scenario is not a good model to explain the
accepted cosmological paradigm, at least, under the parametrization of bulk
viscosity considered in this paper. The main objection against such scenarios
is the absence of conventional radiation and matter-dominated critical points
in the phase space of the model. This entails that radiation and matter
dominance are not generic solutions of the cosmological equations, so that
these stages can be implemented only by means of unique and very specific
initial conditions, i. e., of very unstable particular solutions. Such a
behavior is in marked contradiction with the accepted cosmological paradigm
which requires of an earlier stage dominated by relativistic species, followed
by a period of conventional non-relativistic matter domination, during which
the cosmic structure we see was formed. Also, we found that the bulk viscosity
is positive just until very late times in the cosmic evolution, around z < 1.
For earlier epochs it is negative, been in tension with the local second law of
thermodynamics.
