Prospects for observations of high-energy cosmic tau neutrinos

We study the prospects for the observation of high-energy cosmic tau neutrinos $(E>~{10}^6$ GeV) originating from proton acceleration in the cores of active galactic nuclei. We consider the possibility that vacuum flavor neutrino oscillations induce a tau to muon neutrino flux ratio greatly exceeding the rather small value expected from intrinsic production. The criteria and event rates for under water or ice light Čerenkov neutrino telescopes are given by considering the possible detection of downgoing high-energy cosmic tau neutrinos through characteristic double shower events.