Extremely high energy neutrinos, neutrino hot dark matter, and the highestenergy cosmic rays

Extremely high energy (similar to 10(22) eV) cosmic neutrino beams initiate high energy particle cascades in the background of relic neutrinos from th e big bang. We perform numerical calculations to show that such cascades co uld contribute more than 10% to the observed cosmic ray flux above 3 X 10(1 9) eV if neutrinos have similar to eV masses. The required intensity of pri mary neutrinos could be consistent with astrophysical models far their prod uction if the maximum neutrino energy reaches to similar to 10(22) eV and t he massive neutrino dark matter is locally clustered. Future observations o f ultrahigh energy cosmic rays will lead to an indirect but practical searc h for neutrino dark matter.