Ultrahigh-energy neutrino fluxes and their constraints

Applying our recently developed propagation code we review extragalactic neutrino fluxes above 10¹⁴eV in various scenarios and how they are constrained by current data. We specifically identify scenarios in which the cosmogenic neutrino flux above 10¹⁸eV, produced by pion production of ultrahigh energy cosmic rays outside their sources, is considerably higher than the ``Waxman-Bahcall bound.'' This is easy to achieve for sources with hard injection spectra and luminosities that were higher in the past. Such fluxes would significantly increase the chances to detect ultrahigh energy neutrinos with experiments currently under construction or in the proposal stage.