Can substructure in the Galactic halo explain the ATIC and PAMELA results?
Recently, ATIC and PAMELA measured an anomalously large flux of leptonic cosmic rays which may arise from dark matter self-annihilation. While the annihilation signal predicted for a smooth halo is 102–103 times smaller than the measured excess, the signal can be boosted by the presence of subhalos. We investigate the feasibility of large boost factors using a new Monte Carlo calculation technique that is constrained by previous simulation work on halo substructure. The model accounts for the observed decrease in the amount of substructure with decreasing halo mass and the scatter in halo structural parameters such as the density concentration parameter. Our results suggest that boost factors of ∼102 are highly unlikely and are ruled out at ≳14σ within the context of our model. We conclude that substructure alone, at least with commonly assumed annihilation cross sections, cannot explain the anomalous flux measured by ATIC and PAMELA.
