UHE neutrinos: From conventional to new physics

UHE neutrinos with E>1017eV are produced by ultra-high energy cosmic rays (UHECR) interacting with CMB photons (cosmogenic neutrinos) and by top-down sources, such as topological defects (TDs) and superheavy dark matter (SHDM). Cosmogenic neutrinos are reliably predicted and their fluxes can be numerically evaluated using the observed flux of UHECR. The lower limit for the flux is obtained for the case of pure proton composition of the observed UHECR. The rigorous upper limit for cosmogenic neutrino flux also exists. The maximum neutrino energy is determined by maximum energy of acceleration, which at least for the shock acceleration is expected not to exceed 10211021–1022eV. The top-down sources provide neutrino energies a few orders of magnitude higher, and this can be considered as a signature of these models. UHE neutrino fluxes are discussed for production by SHDM and TDs.