Breit-Wigner enhancement of dark matter annihilation

Abstract

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.