CMB Constraint on Dark Matter Annihilation after Planck 2015
  We update the constraint on the dark matter annihilation cross section by
using the recent measurements of the CMB anisotropy by the Planck satellite. We
fully calculate the cascade of dark matter annihilation products and their
effects on ionization, heating and excitation of the hydrogen, hence do not
rely on any assumption on the energy fractions that cause these effects.
