Cosmic microwave background constraints on coupled dark matter

TL;DR

This paper investigates how a non-minimally coupled dark matter component affects cosmic microwave background measurements, revealing that a significant fraction of dark matter can be coupled without conflicting with current observational data.

Contribution

It introduces a model with coupled dark matter and a scalar field, analyzing its effects on CMB constraints and showing the coupling can be larger than in previous models.

Findings

Up to half of dark matter can be coupled without conflicting with data.

The scalar field's role as non-dark energy allows for stronger coupling constraints.

Coupling effects are discernible in Planck and WMAP polarization measurements.

Abstract

We study CMB constraints on a model with a cosmological constant and a fraction of dark matter non-minimally coupled to a massless scalar field. In this scenario, there is an extra gravity-like fifth force which can affect the evolution of the Universe enough to have a discernible effect on measurements of cosmological parameters. Using Planck and WMAP polarisation data, we find that up to half of the dark matter can be coupled. The coupling can also be several times larger than in models with a single species of cold dark matter coupled to a quintessence scalar field, as the scalar field does not play the role of dark energy and is therefore less constrained by the data.