Towards Determination of the Initial Flavor Composition of Ultrahigh-energy Neutrino Fluxes with Neutrino Telescopes

Abstract

We propose a simple but useful parametrization of the flavor composition of ultrahigh-energy neutrino fluxes produced from distant astrophysical sources: $ϕ^{}_e : ϕ^{}_μ: ϕ^{}_τ= \sin^2 ξ\cos^2 ζ: \cos^2 ξ\cos^2 ζ: \sin^2 ζ$. We show that it is possible to determine or constrain $ξ$ and $ζ$ 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 $ζ$ from zero will signify the existence of cosmic $ν^{}_τ$ and $\barν^{}_τ$ neutrinos at the source, and an accurate value of $ξ$ can be used to test both the conventional mechanism and the postulated scenarios for cosmic neutrino production.