Bounds on the neutrino flux from cosmic sources of relativistic particles

In order to facilitate the identification of possible new physics signature s in neutrino telescopes, such as neutrinos from the annihilation of neutra linos or decaying relics, it is essential to gain full control over the ast rophysical inventory of neutrino sources in the Universe. The total availab le accretion power, the extragalactic gamma ray background and the cosmic r ay proton intensity can be used to constrain astrophysical models of neutri no production in extragalactic sources. The resulting upper limit on the ex tragalactic muon neutrino intensity from cosmic particle accelerators F-v m u ,F-ul approximate to 10(-6) GeV cm(-2) s(-1) sr(-1) combined with a reaso nable minimum intensity of neutrinos due to cosmic rays stored in clusters of galaxies F-v mu .min approximate to 10(-9) GeV cm(-2) s(-1) sr(-1) demar k a zone of opportunity for neutrino astronomy over a broad range of energi es between 100 MeV and 1 EeV. Discovery of this neutrino background would o pen a new era for astronomy and provide the first unobscured view to the ea rly Universe.