Aetherizing Lambda: Barotropic Fluids as Dark Energy

TL;DR

This paper analyzes barotropic fluid models of dark energy, showing they are equivalent to a combination of a cosmological constant and a decelerating fluid, with implications for dark energy behavior and the coincidence problem.

Contribution

It characterizes the asymptotic behaviors of barotropic dark energy models and demonstrates their equivalence to a sum of a cosmological constant and a decelerating fluid.

Findings

Barotropic models are equivalent to a cosmological constant plus a decelerating fluid.

They predict w_{AE} ≥ 0, differing from quintessence.

These models can address the coincidence problem and predict w ≈ -1.

Abstract

We examine the class of barotropic fluid models of dark energy, in which the pressure is an explicit function of the density, p = f(\rho). Through general physical considerations we constrain the asymptotic past and future behaviors and show that this class is equivalent to the sum of a cosmological constant and a decelerating perfect fluid, or "aether", with w_{AE}\ge0. Barotropic models give substantially disjoint predictions from quintessence, except in the limit of \LambdaCDM. They are also interesting in that they simultaneously can ameliorate the coincidence problem and yet "predict" a value of w\approx-1.