Strongly interacting astrophysical neutrinos

Abstract The origin and chemical composition of ultrahigh energy cosmic rays is still an open question in astroparticle physics. The observed large-scale isotropy and also direct composition measurements can be interpreted as an extragalactic proton dominance above the ankle at about 10 10 GeV. Photopion production of extragalactic protons in the cosmic microwave background predicts a cut-off at about 5×10 10 GeV in conflict with excesses reported by some experiments. In this report we will outline a recent statistical analysis [M. Ahlers, A. Ringwald, H. Tu, Astropart. Phys. (in press). Preprint astro-ph/0506698 ] of cosmic ray data using strongly interacting neutrinos as primaries for these excesses.