Ultrahigh Energy Neutrino Interactions (with R. Gandhi, C. Quigg and M. H. Reno); selected publications related to this topic: R. Gandhi, C. Quigg, M.H. Reno and I. Sarcevic, Astropart. Phys. 5, 81 (1996), Nucl. Phys. B78, 475 (1996); Physical Review 58, 093009 (1998).

Recent measurements of the small-x deep-inelastic regime at HERA translate to new expectations for the neutrino-nucleon cross section at ultrahigh energies. We find charge-current and neutral current cross sections to be factor of 4-10 times larger than previous estimates. We have studied consequences of these new results for detection of AGN neutrinos with current and future detectors. Our results indicate that planned neutrino detectors have a very good chance of testing different AGN models, while a kilometer size detector might be able to detect electron neutrinos via W-resonance and also muon neutrinos predicted in models for neutrinos from Topological Defects Formed in the Early Universe.