1206.0986 (Hermano Velten et al.)

On the dissipation of the dark matter    [PDF]

Hermano Velten, Dominik Schwarz

Fluids often display dissipative properties. We explore dissipation in the form of bulk viscosity in the cold dark matter fluid. We constrain this model using current data from supernovae, baryon acoustic oscillations and the cosmic microwave background. Considering the isotropic and homogeneous background only, viscous dark matter is allowed to have a bulk viscosity $\lesssim 10^7$ Pa$\cdot$s, also consistent with the expected integrated Sachs-Wolfe effect (which plagues some models with bulk viscosity). We also investigate the small-scale formation of viscous dark matter halos. This analysis places significantly stronger constraints on the dark matter viscosity. The existence of dwarf galaxies is guaranteed only for very small values of the dark matter viscosity, $\lesssim 10^{-3}$ Pa$\cdot$s.

View original: http://arxiv.org/abs/1206.0986