Matter power spectrum for the generalized Chaplygin gas model: The relativistic case

The generalized Chaplygin gas model is the prototype of a unified model of dark energy and dark matter (DM). It is characterized by equation-of-state parameters A and α. We use a statistical analysis of the 2dFGRS data to constrain these parameters. In particular, we find that very small (close to zero) and very large values (α>>1) of the equation-of-state parameter α are preferred. To test the validity of this type of unification of the dark sector we admit the existence of a separate DM component in addition to the Chaplygin gas and calculate the probability distribution for the fractional contributions of both components to the total energy density. This analysis favors a model for which the Universe is nearly entirely made up of the separate DM component with an almost negligible Chaplygin gas part. This confirms the results of a previous Newtonian analysis.