Astrophysical sources of high-energy neutrinos

Neutrino telescopes of the cubic-kilometer scale will be able to discover the diffuse, isotropic flux of ∼ (5 10−8- 5 10−7) GeV cm−2 s−1 st−1 due to unresolved extragalactic sources of relativistic protons at energies above ∼ 100 TeV above which the atmospheric background practically vanishes. For the brightest point sources with an expected flux in the range ∼ (10−9- 10−10) GeV cm−2 s−1, a detection is possible in long-term exposures. The galactic disk and the extragalactic isotropic background are expected to be the strongest diffuse sources. As judged from their much stronger contribution to the extragalactic gamma ray background, blazars seem to be more important as high energy neutrino sources than GRBs by more than an order of magnitude. Flavor mixing due to oscillations could render an extragalactic flux of neutrinos from neutralino annihilations detectable with cubic-kilometer neutrino telescopes, if flavor discrimination at energies in the 10-100 GeV regime will be achieved.