ULTRAHIGH ENERGY NEUTRINOS

The ultrahigh energy neutrino cross section is well understood in the standard model for neutrino energies up to 10¹² GeV. Tests of neutrino oscillations (v_µ ↔ ν_τ) from extragalactic sources of neutrinos are possible with large underground detectors. Measurements of horizontal air shower event rates at neutrino energies above 10¹⁰ GeV will be able to constrain nonstandard model contributions to the neutrino-nucleon cross section, e.g., from mini-black hole production.