Viscous universe with cosmological constant

We investigated a bulk viscous fluid universe with cosmological constant Λ 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 nonzero constant and tends to this nonzero constant in the future. We show that the bulk viscosity model has a significantly better fitting to the combined SNe Ia + CMB + BAO + H(z) data than the ΛCDM 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 ΛCDM 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 ΛCDM model and the other “dark energy” model.