Non-adiabatic instability in coupled dark sectors

TL;DR

This paper identifies conditions for stable coupled dark matter-dark energy models without non-adiabatic instabilities and tests a specific interaction model against cosmological data, revealing parameter correlations.

Contribution

It provides a general method to identify stable coupled dark sector models and analyzes a specific proportional interaction model with observational data.

Findings

Stable models can be characterized by a generic coupling Q and dark energy equation of state w.

The proportional interaction model fits cosmological data well.

Coupling affects neutrino mass constraints.

Abstract

It has been recently pointed out that coupled dark matter-dark energy systems suffer from non-adiabatic instabilities at early times and large scales. We show how coupled models free from non-adiabatic instabilities can be identified as a function of a generic coupling Q and of the dark energy equation of state w. In our analysis, we do not refer to any particular cosmic field. We also confront a viable class of model in which the interaction is directly proportional to the dark energy density to recent cosmological data. In that framework, we show the correlations between the dark coupling and several cosmological parameters allowing to e.g.larger neutrino mass than in uncoupled models.