Constraints on Dark Matter Annihilation Cross Section in Scenarios of
  Brane-World and Quintessence
  We investigate the dark matter annihilation in the brane-world and
quintessence scenarios, in which the modified cosmological expansion rate can
enhance the thermal relic density of dark matter. According to the observed
dark matter abundance, we constrain the thermally averaged annihilation cross
section <\sigma v> in these two scenarios. In addition, the big bang
nucleosynthesis and the partial-wave unitarity are also used to place bounds on
<\sigma v>. It is found that both scenarios can lead to a large annihilation
cross section, so they can be used to explain the recent PAMELA, ATIC and
PPB-BETS anomalies.
