Cosmological gamma ray and neutrino backgrounds due to neutralino dark matter annihilation

We compute the cosmological background radiation of gamma rays and neutrinos due to neutralino annihilation in evolving dark matter halos, assuming the observed dark matter is comprised of thermally excited neutralinos in the MSSM. The spectrum of this gamma-ray background radiation does not show strong annihilation line features, but could amount to a significant fraction of the extragalactic gamma ray continuum flux observed by EGRET above a few GeV. The corresponding cosmological neutrino background is weak compared to the atmospheric foreground. Assuming full mixing, however, the cosmological tau-neutrino background could be detectable with a flavor-discriminating neutrino telescope in the energy range 10 GeV - 1 TeV. A small anisotropy of the background radiation is expected, reflecting the local clustering of dark matter halos along the supergalactic plane.