Cosmological Effects of a Class of Fluid Dark Energy Models

We study the impact of a generalized Chaplygin gas as a candidate for dark energy on CMB anisotropies. The generalized Chaplygin gas is a fluid component with an exotic equation of state, $p = - A/\rho^\alpha$ (a polytropic gas with negative constant and exponent). Such component interpolates in time between dust and a cosmological constant, with an intermediate behaviour as $p=\alpha \rho$. Perturbations of this fluid are stable on small scales, but behave in a very different way with respect to standard quintessence. Moreover, a generalized Chaplygin gas could also represent an archetypal example of a phenomenological unified models of dark energy and dark matter. The results presented here show how the CMB anisotropies induced by this class of models differ from a $\Lambda$CDM model.