Reconstructing the expansion history of the Universe with a one-fluid approach

Assuming that the Universe is filled by one single fluid, we present in the context of General Relativity a possible explanation for the acceleration of the Universe. We use ordinary thermodynamics and the fact that small matter perturbations barely propagate in our Universe, to derive a general solution for a single fluid in which the speed of sound vanishes. We find a model that contains $\Lambda$CDM as a special case, and is compatible with current observational data.