Linear and non-Linear Instabilities in Unified Dark Energy Models

TL;DR

This paper examines the complex nonlinear instabilities in unified dark energy models, emphasizing the importance of full nonlinear analysis and exploring observational distinctions among different dark fluid models.

Contribution

It provides clearer derivations of key results, including the relation between generalized Chaplygin gas and $\\Lambda$CDM, and investigates small-scale instabilities in coupled dark energy models.

Findings

Highlighting the need for nonlinear treatment in dark energy models

Deriving the relation between generalized Chaplygin gas and $\\Lambda$CDM

Identifying Jeans-type small-scale instability in coupled models

Abstract

We revisit the paradigm of unified dark energy discussing in detail the averaging problem in this type of scenarios, highlighting the need for a full non-linear treatment. We also address the question of if and how models with one or several dark fluids can be observationally distinguished. Simpler and physically clearer derivations of some key results, most notably on the relation between the generalized Chaplygin gas and the standard ($\Lambda$CDM) `concordance' model and on a Jeans-type small-scale instability of some coupled dark energy/dark matter models are presented.