CMB bounds on dark matter annihilation: Nucleon energy-losses after
  recombination
  We consider the propagation and energy losses of protons and anti-protons
produced by dark matter annihilation at redshifts 100<z<~2000. In the case of
dark matter annihilations into quarks, gluons and weak gauge bosons, protons
and anti-protons carry about 20% of the energy injected into e^\pm and
\gamma's, but their interactions are normally neglected when deriving cosmic
microwave background bounds from altered recombination histories. Here, we
follow numerically the energy-loss history of typical protons/antiprotons in
the cosmological medium. We show that about half of their energy is channeled
into photons and e^\pm, and we present a simple prescription to estimate the
corresponding strengthening of the cosmic microwave background bounds on the
dark matter annihilation cross section.
