Ultrahigh energy cosmic neutrinos and the physics beyond the Standard Model

We study ultrahigh energy astrophysical neutrinos and their interactions. We find that for GZK neutrinos three flavor mixing is important and the neutrino flavor ratio at Earth deviates from 1:1:1. We show the effect of tau neutrino regeneration and tau energy loss as they propagate through the Earth. We also consider production of mini black holes, neutrino interactions via TeV string resonances and the supersymmetric charged sleptons (stau) production in neutrino interactions. We discuss signals for these processes in detectors such as Anita, EUSO and OWL.