Júlio C. Fabris (DF UFES/Brazil and IAP/France)

An exotic fluid that can play the role at the same time of dark energy and dark matter, Chaplygin gas model, has emerged first in the context of string theory. Later this unified model for the cosmological dark sector has been generalized in many different ways. A dark viscous model has been proposed more recently as another possible unification of the two dark components. We review the theoretical foundations for those unified models for the dark sector. Later, we consider some specific models, in particular the Generalized Chaplygin gas model and the viscous fluid model, discussing the corresponding observational evidences. Special attention will be played for the supernovae type Ia data and the structure formation problem. The models analyzed seem to satisfy the constraints given by observation for a large range of values of their free parameters. In particular, the observational data for matter power spectrum seem do not rule out this unified model, contrarily to what has been claimed many times in the literature.