  The collisions between accelerated protons and the photons present in cosmos
can be a main source of high-energy neutrinos (E \geq 10^6 GeV) of all flavors
above the atmospheric neutrino background. I discuss here the possibility of
photohadronic production of high-energy cosmic tau neutrinos in an
astrophysical site and study some of the effects of vacuum neutrino flavor
mixing on their subsequent propagation. I also discuss the prospects for
observations of these high-energy cosmic tau neutrinos in new large neutrino
telescopes
