Implications of leptonic unitarity violation at neutrino telescopes

A measurement of the ultrahigh-energy (UHE) cosmic neutrinos at a km3-size neutrino telescope will open a new window to constrain the 3×3 neutrino mixing matrix V and probe possible new physics. We point out that it is in principle possible to examine the non-unitarity of V, which is naturally expected in a class of seesaw models with one or more TeV-scale Majorana neutrinos, by using neutrino telescopes. Considering the UHE neutrinos produced from the decays of charged pions arising from pp and (or) pγ collisions at a distant astrophysical source, we show that their flavor ratios at a terrestrial neutrino telescope may deviate from the democratic flavor distribution ϕeT:ϕμT:ϕτT=1:1:1 due to the seesaw-induced unitarity violation of V. Its effect can be as large as several percent and can serve for an illustration of how sensitive a neutrino telescope should be to this kind of new physics.