Constraints on dark matter annihilation from CMB observations before
  Planck
  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.
