Can substructure in the Galactic Halo explain the ATIC and PAMELA results?

TL;DR

This paper investigates whether substructure in the Galactic Halo can explain the excess cosmic ray flux observed by ATIC and PAMELA, concluding that typical substructure models cannot account for the anomalies.

Contribution

The study introduces a new Monte Carlo method constrained by simulations to evaluate the impact of halo substructure on cosmic ray flux boosts.

Findings

Boost factors of about 10^2 are statistically ruled out.

Substructure alone cannot explain the observed excess flux.

Commonly assumed dark matter annihilation cross-sections are insufficient.

Abstract

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 10^2-10^3 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 the order of 10^2 are ruled out at more than 14 sigma. We conclude that substructure alone, at least with commonly assumed annihilation cross-sections, cannot explain the anomalous flux measured by ATIC and PAMELA.