Turbulence and little rip cosmology

Abstract

A variety of conditions are considered under which the cosmic dark fluid may be able to develop a future Big Rip or Little Rip singularity. Both one-component and two-component models are considered. In the latter case we present a way in which the fluid can be decomposed into two components, one nonturbulent (ideal) and one turbulent part, obeying two different equations of state. For the nonturbulent part, the thermodynamical parameter, commonly called $w$, is assumed to be less than $\ensuremath{-}1$ throughout. For the turbulent part, it turns out that it is sufficient that ${w}_{\mathrm{turb}}$ lies in the quintessence region in order to lead to a singularity. Both Big Rip and Little Rip behavior for dark energy are found. In the one-component case, we examine how the universe may develop from a viscous era with constant bulk viscosity into a turbulent era, the turbulence in effect protecting the universe from encountering the singularity at all. The equivalent description of the same cosmology in terms of inhomogeneous (imperfect) fluid is also presented.