Propagation of ultrahigh energy neutrinos in the black-body neutrino field

Abstract

We discuss the propagation of ultrahigh energy (UHE) neutrinos with energies ranging up to the grand unification (GUT) scale. In this energy range, the Universe becomes opaque for UHE neutrinos due to interactions with black-body neutrinos (ν bb) and the UHE neutrinos propagate cascading if the sources produce neutrinos at high redshift epochs ( z ⪢ 10). The absorption due to the energy loss and the cascade development in the black-body neutrino field may lead to a pile-up and a cut-off in the energy spectrum of UHE neutrinos emitted at an early epoch. However, these modifications will be smeared if many sources distributed universally from early epochs to the present contribute to the bulk of the UHE neutrinos. In this case, the main effect of the cosmic neutrino background on the UHE neutrino spectrum is to change the spectral slope and knowledge of the primary energy distribution of UHE neutrinos and the source evolution in the Universe is indispensable for reliable inferences of the presence of the cosmic neutrino background from observations of the UHE neutrino spectrum.