CCAST, World Lab, Beijing 100080, Peoples R China
; Chinese Acad Sci, Inst High Energy Phys, Beijing 100049, Peoples R China
We propose a simple but useful parametrization of the flavor composition of ultrahigh-energy neutrino fluxes produced from distant astrophysical sources: phi(e)phi(mu)phi(tau)=sin(2)xi cos(2)zeta cos(2)xi cos(2)zeta sin(2)zeta. We show that it is possible to determine or constrain xi and zeta by observing two independent neutrino flux ratios at the second-generation neutrino telescopes, provided three neutrino mixing angles and the Dirac CP-violating phase have been well measured in neutrino oscillations. Any deviation of zeta from zero will signify the existence of cosmic nu(tau) and (nu) over bar (tau) neutrinos at the source, and an accurate value of xi can be used to test both the conventional mechanism and the postulated scenarios for cosmic neutrino production.