Bulk viscous cosmology: unified dark matter
  The bulk viscosity is introduced to model unified dark matter. The viscous
unified model assumes the universe is filled with a single fluid with the bulk
viscosity. We review the general framework of the viscous cosmology. The Hubble
parameter has a direct connection with the bulk viscosity coefficient. For
concrete form of the bulk viscosity, the Hubble parameter which has the scaling
relation with the redshift can be obtained. We discuss two viscosity models and
the cosmological evolution to which they lead. Using SNe Ia data, the viscosity
model can be fitted. We briefly review the fitting method here.
