Viscous universe with cosmological constant

Abstract

We investigated a bulk viscous fluid universe with cosmological constant {\Lambda} by assuming that the bulk viscosity to be proportional to the Hubble parameter. We found that for an expanding universe, the (relative) matter density will be always greater than a non-zero constant, and tends to this non-zero constant in the future. We show that the bulk viscosity model has a significantly better fitting to the combined SNeIa + CMB + BAO + H(z) data than the {\Lambda}CDM model. Generally, the evolution or values of some cosmological parameters predicted by the bulk viscosity model do not deviate significantly from which are obtained from the {\Lambda}CDM model since the bulk viscosity coefficient obtained from the astronomical observational data is so small. We also made a statefinder analysis of the bulk viscosity model and found that the evolution of the {r, s} parameters behaves in such a way that 0 < s < 1, 0.945 < r <1, indicating the bulk viscosity model is different from the {\Lambda}CDM model.