Viscosity-Induced Crossing of the Phantom Barrier

TL;DR

This paper demonstrates that bulk viscosity in cosmic fluid can cause the universe's dark energy state to cross the phantom barrier, suggesting it is a gradual transition rather than a strict boundary, with implications for future singularities.

Contribution

It provides a model showing how viscosity can induce crossing of the phantom barrier in dark energy, supported by astrophysical data and thermodynamical analysis.

Findings

Viscosity can drive the crossing of the phantom barrier.

The phantom barrier is a fuzzy concept, not a strict boundary.

Thermodynamical quantities near the Big Rip are calculated.

Abstract

We show explicitly, by using astrophysical data plus reasonable assumptions for the bulk viscosity in the cosmic fluid, how the magnitude of this viscosity may be high enough to drive the fluid from its position in the quintessence region at present time $t=0$ across the barrier $w=-1$ into the phantom region in the late universe. The phantom barrier is accordingly not a sharp mathematical divide, but rather a fuzzy concept. We also calculate the limiting forms of various thermodynamical quantities, including the rate of entropy production, for a dark energy fluid near the future Big Rip singularity.