CMB photons shedding light on dark matter
  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.
