Breit-Wigner Enhancement of Dark Matter Annihilation
  We point out that annihilation of dark matter in the galactic halo can be enhanced relative to that in the early universe due to a Breit-Wigner tail, if the dark matter annihilates through a pole just below the threshold. This provides a new explanation to the "boost factor" which is suggested by the recent data of the PAMELA, ATIC and PPB-BETS cosmic-ray experiments. 
Masahiro Ibe, Hitoshi Murayama, T. T. Yanagida