Phenomenological equation of state and late-time cosmic acceleration

TL;DR

The paper introduces a phenomenological equation of state for a flat universe with a perfect fluid, explaining late-time cosmic acceleration and aligning with some scalar field dark energy models under specific conditions.

Contribution

It proposes a universal function for the pressure-density ratio in cosmology and demonstrates its consistency with observational constraints and scalar field models.

Findings

The proposed ratio aligns with late-time acceleration observations.

Scalar field models can match the ratio if matter density is below 0.23.

Current matter density measurements conflict with the model's requirements.

Abstract

Assuming a flat Friedmann-Robertson-Walker cosmology with a single perfect fluid, we propose a pressure-density ratio that evolves as a specific universal function of the scale parameter. We show that such a ratio can indeed be consistent with several observational constraints including those pertaining to late-time accelerated expansion. Generic dynamical scalar field models of Dark energy (with quadratic kinetic terms in their Lagrange density) are shown to be in accord with the proposed equation-of-state ratio, provided the current matter density parameter $\Omega_{m0} < 0.23$ - a value {\it not} in agreement with recent measurements.