Zhou, S (reprint author), Chinese Acad Sci, Inst High Energy Phys, Beijing 100049, Peoples R China.
A measurement of the ultrahigh-energy (UHE) cosmic neutrinos at a km(3)-size neutrino telescope will open a new window to constrain the 3 x 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) p gamma collisions at a distant astrophysical source, we show that their flavor ratios at a terrestrial neutrino telescope may deviate from the democratic flavor distribution phi(T)(e):phi(T)(mu):phi(T)(tau) = 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. (C) 2008 Elsevier B.V. All rights reserved.