Observational Constraints on bulk viscous matter-dominated models
Montiel, Ariadna (Centro de Investigación y Estudios Avanzados del IPN)

In this work, we study the range of consistency of a constant bulk viscosity model where the dark sector of the cosmic substratum is a viscous fluid with pressure $p= -\zeta \theta$, with $\theta$ the fluid-expansion scalar and $\zeta$ the coefficient of bulk viscosity. We found that the best fit for the viscosity parameter $\tilde{\zeta}$ is in the range $0<\tilde{\zeta}<3$, in agreement with the prediction of the model and previous probes. In this analysis, we also include the CMB5-year data and CMB7-year data, as well as with the baryonic acoustic peak BAO. We use the updated sample of 59 high-redshift GRBs reported by Wei (2010) calibrated at low redshifts with the Union 2 sample of SNe Ia. From the statistics with CMB it turns out that the model is only in very good concordance for epochs as far as $z\sim 8.1$ till present.