Constraints on dark matter annihilation from CMB observations before Planck

TL;DR

This paper derives constraints on dark matter annihilation cross sections using pre-Planck CMB data, considering realistic energy deposition and halo models, and finds that these constraints exclude thermal relic cross sections below certain masses.

Contribution

It provides updated bounds on dark matter annihilation cross sections before Planck, incorporating detailed energy deposition and halo models, improving the understanding of dark matter's impact on the early universe.

Findings

Excludes thermal relic cross section below 30 GeV for e+e- channel.

Excludes thermal relic cross section below 15 GeV for mu+mu- channel.

Constraints remain robust despite uncertainties in halo modeling.

Abstract

We compute the bounds on the dark matter (DM) annihilation cross section using the most recent Cosmic Microwave Background measurements from WMAP9, SPT'11 and ACT'10. We consider DM with mass in the MeV-TeV range annihilating 100% into either an e+e- or a mu+mu- pair. We consider a realistic energy deposition model, which includes the dependence on the redshift, DM mass and annihilation channel. We exclude the canonical thermal relic abundance cross section (<sigma v> = 3 x 10^{-26} cm^3 s^{-1}) for DM masses below 30 GeV and 15 GeV for the e+e- and mu+mu- channels, respectively. A priori, DM annihilating in halos could also modify the reionization history of the Universe at late times. We implement a realistic halo model taken from results of state-of-the-art N-body simulations and consider a mixed reionization mechanism, consisting on reionization from DM as well as from first stars. We find that the constraints on DM annihilation remain unchanged, even when large uncertainties on the halo model parameters are considered.