Substructure Boosts to Dark Matter Annihilation from Sommerfeld
  Enhancement
  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.
