Bulk viscosity driving the acceleration of the Universe

The possibility that the present acceleration of the Universe is driven by a kind of viscous fluid is exploited. At background level this model is similar to the generalized Chaplygin gas model (GCGM). But, at the perturbative level, the viscous fluid exhibits interesting properties. In particular the oscillations in the power spectrum that plagues the GCGM are not present. Possible fundamental descriptions for this viscous dark energy are discussed.