CMB photons shedding light on dark matter

TL;DR

This paper investigates how dark matter annihilation impacts the cosmic microwave background and reionization, providing updated constraints and proposing models that align with observations but face temperature bounds.

Contribution

It offers new constraints on dark matter annihilation rates using CMB data and explores halo-based reionization models consistent with observations.

Findings

Dark matter annihilation affects CMB anisotropies.

Halo-based annihilation models can explain reionization patterns.

Stronger bounds on annihilation cross-section when including IGM temperature constraints.

Abstract

The annihilation or decay of Dark Matter (DM) particles could affect the thermal history of the universe and leave an observable signature in Cosmic Microwave Background (CMB) anisotropies. We update constraints on the annihilation rate of DM particles in the smooth cosmological background, using WMAP7 and recent small-scale CMB data. With a systematic analysis based on the Press-Schechter formalism, we also show that DM annihilation in halos at small redshift may explain entirely the reionization patterns observed in the CMB, under reasonable assumptions concerning the concentration and formation redshift of halos. We find that a mixed reionization model based on DM annihilation in halos as well as star formation at a redshift z~6.5 could simultaneously account for CMB observations and satisfy constraints inferred from the Gunn-Peterson effect. However, these models tend to reheat the inter-galactic medium (IGM) well above observational bounds: by including a realistic prior on the IGM temperature at low redshift, we find stronger cosmological bounds on the annihilation cross-section than with the CMB alone.