Phantom dark energy as an effect of bulk viscosity

TL;DR

This paper explores how bulk viscosity in a homogeneous universe can mimic phantom dark energy effects, suggesting non-equilibrium pressure as a potential cause for accelerated cosmic expansion.

Contribution

It demonstrates the degeneracy in bulk viscous cosmologies and establishes conditions linking viscous effects to phantom dark energy using observational constraints.

Findings

Bulk viscosity can replicate phantom dark energy behavior.

Conditions identified for matter and radiation viscous cosmologies to mimic dark energy.

Observational data constrains the parameters of viscous cosmological models.

Abstract

In a homogeneous and isotropic universe bulk viscosity is the unique viscous effect capable to modify the background dynamics. Effects like shear viscosity or heat conduction can only change the evolution of the perturbations. The existence of a bulk viscous pressure in a fluid, which in order to obey to the second law of thermodynamics is negative, reduces its effective pressure. We discuss in this study the degeneracy in bulk viscous cosmologies and address the possibility that phantom dark energy cosmology could be caused by the existence of non-equilibrium pressure in any cosmic component. We establish the conditions under which either matter or radiation viscous cosmologies can be mapped into the phantom dark energy scenario with constraints from multiple observational data-sets