Substructure Boosts to Dark Matter Annihilation from Sommerfeld Enhancement

TL;DR

This paper demonstrates that substructure and Sommerfeld enhancement significantly increase dark matter annihilation signals, potentially making them detectable by gamma-ray telescopes like Fermi.

Contribution

It introduces a comprehensive analysis of how substructure and velocity effects amplify dark matter annihilation signals, leading to very large boost factors.

Findings

Boost factors of 10^5 to 10^9 are achievable.

Enhanced signals can outshine background gamma-ray flux.

Detection prospects with Fermi are promising.

Abstract

The recently introduced Sommerfeld enhancement of the dark matter annihilation cross section has important implications for the detection of dark matter annihilation in subhalos in the Galactic halo. In addition to the boost to the dark matter annihilation cross section from the high densities of these subhalos with respect to the main halo, an additional boost caused by the Sommerfeld enhancement results from the fact that they are kinematically colder than the Galactic halo. If we further believe the generic prediction of CDM that in each subhalo there is an abundance of substructure which is approximately self-similar to that of the Galactic halo, then I show that additional boosts coming from the density enhancements of these small substructures and their small velocity dispersions enhance the dark matter annihilation cross section even further. I find that very large boost factors ($10^5$ to $10^9$) are obtained in a large class of models. The implications of these boost factors for the detection of dark matter annihilation from dwarf Spheroidal galaxies in the Galactic halo are such that, generically, they outshine the background gamma-ray flux and are detectable by the Fermi Gamma-ray Space Telescope.