Abstract: (IOP)
In the upcoming decade, observatories for cosmic neutrinos will open up a huge window in energy from 107GeV to 1017GeV, much above the Greisen-Zatsepin-Kuzmin (GZK) cutoff at about 4×1010GeV, expected for cosmic protons and nuclei due to inelastic interactions with the cosmic microwave background photons. In this review, we discuss in particular the possibilities to use extremely energetic cosmic neutrinos as a diagnostic of astrophysical processes, as a tool for particle physics beyond the Standard Model, and as a probe of cosmology.