1205.0613 (Arturo Avelino)

Interacting viscous matter with a dark energy fluid    [PDF]

Arturo Avelino

We study a cosmological model composed of a matter fluid interacting with a dark fluid in a spatially flat Universe. The matter component represents the baryon and dark matter and it is taken into account, through a bulk viscosity, the irreversible process that the matter fluid undergoes because of the accelerated expansion of the universe. The bulk viscous coefficient is assumed to be proportional to the Hubble parameter. The interaction term between the fluids is not assumed a priori but it is expressed in terms of the barotropic indexes of the fluids, which are considered as a function of the ratio between their energy densities. The radiation component is also taken into account in the model. The model is constrained using the type Ia supernova observations, the shift parameter of the CMB, the acoustic peak of the BAO and the Hubble expansion rate, to constrain the values of the barotropic index of dark energy and the bulk viscous coefficient. It is found that the bulk viscosity is constrained to be negligible (around zero) from the observations and that the barotropic index for the dark energy to be negative and close to zero too, indicating a phantom energy.

View original: http://arxiv.org/abs/1205.0613