IMPROVEMENTS ON A UNIFIED DARK MATTER MODEL

We study, by means of a spherical collapse model, the effect of shear, rotation, and baryons on a generalized Chaplygin gas (gCg) dominated universe. We show that shear, rotation, and the presence of baryons slow down the collapse compared to the simple spherical collapse model. The slowing down in the growth of density perturbation is able to solve the instability of the unified dark matter (UDM) models described in previous papers (e.g. Sandvik et al. 2004) at the linear perturbation level, as also shown by a direct comparison of our model with previous results.