Dark Coupling and Gauge Invariance

TL;DR

This paper investigates a gauge-invariant coupled dark energy-dark matter model with energy exchange proportional to the Hubble rate, deriving perturbation equations and analyzing observational constraints with WMAP data.

Contribution

It introduces a gauge-invariant formulation of coupled dark energy-dark matter perturbations and performs the first comprehensive likelihood analysis with CMB data.

Findings

Perturbation equations consistent with gauge invariance derived.

Initial conditions found to be adiabatic for dark energy.

Model constrained using WMAP 7-year data.

Abstract

We study a coupled dark energy-dark matter model in which the energy-momentum exchange is proportional to the Hubble expansion rate. The inclusion of its perturbation is required by gauge invariance. We derive the linear perturbation equations for the gauge invariant energy density contrast and velocity of the coupled fluids, and we determine the initial conditions. The latter turn out to be adiabatic for dark energy, when assuming adiabatic initial conditions for all the standard fluids. We perform a full Monte Carlo Markov Chain likelihood analysis of the model, using WMAP 7-year data.