Hunting for Ultra High Energy Neutrinos

I will discuss propagation of ultra high energy (UHE) neutrinos in the cosmic neutrino background, and explain both the resonant and the non-resonant absorption effects by including the thermal distribution of the background neutrino momenta. I will show that top-down sources at redshifts z > 10, such as decaying superheavy dark matter, cosmic strings and cosmic necklaces, exhibit resonant flux suppression around energies 10^12-10^13 GeV whereas cosmogenic neutrinos and astrophysical neutrino sources, such as active galactic nuclei and gamma ray bursts, are not affected since such high energies are not expected to be reached for those. I will discuss the observation prospects of UHE neutrinos at JEM-EUSO, LOFAR and SKA. Finally, I will argue that the observation of resonant flux suppression would indicate UHE neutrino sources beyond z~10, and thus, would favor top-down neutrino sources.