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.