The Impact of Halo Substructure on Dark Matter Signatures

PAMELA/FERMI/HESS data on positrons may be explained in terms of solar neighbourhood WIMP annihilations primarily to leptons or muons for a few TeV mass WIMP with a Sommerfeld-corrected boost ∼104−105, provided that a small component of the dark matter is in cold subhalo substructure. Saturation of the Sommerfeld effect constrains the range of contributing substructures to be above ∼105M⊙. Dynamical friction and tidal disruption of substructure in the inner regions of halos and subhalos play an important role in suppressing annihilations. The associated diffuse gamma ray or synchrotron signal from the inner galaxy is below current limits, but an inverse Compton contribution produced in early universe substructure annihilations is potentially detectable by FERMI as an isotropic background.