Cosmological Fluids with Logarithmic Equation of State

TL;DR

This paper explores cosmological models with fluids characterized by a logarithmic equation of state and bulk viscosity, demonstrating their ability to explain late-time acceleration and match observational data.

Contribution

It introduces novel cosmological scenarios with logarithmic equations of state and viscosity, analyzing their dynamical behavior and observational consistency.

Findings

Scenarios can trigger transition from deceleration to acceleration.

Models show excellent agreement with SN Ia and Hubble data.

Existence of asymptotic accelerating attractors, including de Sitter-like states.

Abstract

We investigate the cosmological applications of fluids having an equation of state which is the analog to the one related to the isotropic deformation of crystalline solids, that is containing logarithmic terms of the energy density, allowing additionally for a bulk viscosity. We consider two classes of scenarios and we show that they are both capable of triggering the transition from deceleration to acceleration at late times. Furthermore, we confront the scenarios with data from Supernovae type Ia (SN Ia) and Hubble function observations, showing that the agreement is excellent. Moreover, we perform a dynamical system analysis and we show that there exist asymptotic accelerating attractors, arisen from the logarithmic terms as well as from the viscosity, which in most cases correspond to a phantom late-time evolution. Finally, for some parameter regions we obtain a nearly de Sitter late-time attractor, which is a significant capability of the scenario since the dark energy, although dynamical, stabilizes at the cosmological constant value.