Dark Matter Annihilation to Electrons, Neutrinos and Gamma Rays

We examine dark matter annihilation in galaxy halos. By considering annihilation into all Standard Model particles we show that the least detectable final states, namely neutrinos, define a strong general upper bound on the total cross section. This limit implies annihilation cannot significantly modify dark matter halo density profiles. We also consider dark matter annihilation into charged particles, which is necessarily accompanied by gamma rays, produced via radiative corrections. Internal bremsstrahlung from the final state particles produce hard gamma rays up to the dark matter mass, with an approximately model-independent spectrum, allowing robust upper bounds on the dark matter self annihilation cross section to e(+/-) to be determined from Galactic gamma ray data.