Viscous Little Rip Cosmology

TL;DR

This paper introduces a viscous Little Rip cosmology, demonstrating that viscosity can lead to a universe avoiding finite-time singularities, and explores the physical implications of this model for cosmic structure dissolution.

Contribution

It shows that viscosity effects can produce a Little Rip scenario, offering a new perspective on dark energy models and universe evolution.

Findings

Viscosity can induce Little Rip cosmology without leading to a Big Rip.

Viscous fluids can produce a Little Rip through inhomogeneous equations of state.

Physical interpretation of structure dissolution in Little Rip universe provided.

Abstract

Dark energy of phantom or quintessence nature with an equation of state parameter $w$ almost equal to -1 often leads the universe evolution to a finite-time future singularity. An elegant solution to this problem has been recently proposed \cite{frampton11} under the form of the so-called Little Rip cosmology which appears to be a realistic alternative to the $\Lambda$CDM model. A viscous Little Rip cosmology is here proposed. Whereas generically bulk viscosity tends to promote the Big Rip, we find that there are a number of situations where this is not the case and where the formalism nicely adjusts itself to the Little Rip scenario. We prove, in particular, that a viscous fluid (or, equivalently, one with an inhomogeneous (imperfect) equation of state) is perfectly able to produce a Little Rip cosmology as a purely viscosity effect. The possibility of its induction as a combined result of viscosity and a general (power-like) equation of state is also investigated in detail. To finish, a physical, inertial force interpretation of the dissolution of bound structures in the Little Rip cosmology is presented.