No stable dissipative phantom scenario in the framework of a complete cosmological dynamics

TL;DR

This study analyzes the phase space of a cosmological model with bulk viscosity, finding that stable phantom solutions are not possible unless bulk viscosity is nearly zero, which still allows a transition to accelerated expansion.

Contribution

It demonstrates that in a complete cosmological framework with bulk viscosity, stable viscous phantom solutions cannot exist, clarifying the limitations of such models.

Findings

Stable viscous phantom solutions are not allowed.

Near-zero bulk viscosity enables transition to accelerated expansion.

Model supports transition from radiation to dark energy dominance.

Abstract

We investigate the phase space dynamics of a bulk viscosity model in the Eckart approach for a spatially flat Friedmann-Robertson-Walker universe. We have included two barotropic fluids and a dark energy component. One of the barotropic fluids is treated as an imperfect fluid having bulk viscosity, whereas the other components are assumed to behave as perfect fluids. Both barotropic fluids are identified as either radiation or dark matter. Considering that the bulk viscosity acts on either radiation or dark matter, we find that viscous phantom solutions with stable behavior are not allowed in the framework of complete cosmological dynamics. Only an almost zero value of the bulk viscosity allows a transition from a radiation-dominated to a matter-dominated epoch, which then evolves to an accelerated late time expansion, dominated by dark energy.