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Abstract: Unified Dark Matter models describe Dark Matter and Dark Energy as a singleentity which is, in the simplest case, embodied in a perfect barotropic fluid.It is a well-established fact that small adiabatic perturbations of UnifiedDark Matter have an evolution characterised by oscillations and decay whichprovide predictions on the Cosmic Background Radiation anisotropies which arein poor agreement with observation. In this paper we investigate thegeneralised Chaplygin gas and we find that the Integrated Sachs-Wolfe effectexcludes the model for $10^{-3} < \alpha < 350$. We discuss the implications onthe background evolution of the Universe if large values of $\alpha$ areconsidered. In this case, the Universe expansion mimics a matter-dominatedphase abruptly followed by a de Sitter one at the transition redshift $z tr$.Thanks to an analysis of the type Ia supernovae Constitution set we are able toplace $z tr = 0.22$.



Author: Oliver F. Piattella

Source: https://arxiv.org/



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