Bounds on the neutrino flux from cosmic sources of relativistic particles

In order to facilitate the identification of possible new physics signatures in neutrino telescopes, such as neutrinos from the annihilation of neutralinos or decaying relics, it is essential to gain full control over the astrophysical inventory of neutrino sources in the Universe. The total available accretion power, the extragalactic gamma ray background and the cosmic ray proton intensity can be used to constrain astrophysical models of neutrino production in extragalactic sources. The resulting upper limit on the extragalactic muon neutrino intensity from cosmic particle accelerators Fνμ,ul ∼ 10-6 GeV cm-2 s-1 sr-1 combined with a reasonable minimum intensity of neutrinos due to cosmic rays stored in clusters of galaxies Fνμ,min ∼ 10-9 GeV cm-2 s-1 sr-1 demark a zone of opportunity for neutrino astronomy over a broad range of energies between 100 MeV and 1 eV. Discovery of this neutrino background would open a new era for astronomy and provide the first unobscured view to the early Universe. (author)