Unitarity Bounds of Astrophysical Neutrinos

TL;DR

This paper derives general unitarity-based bounds on the flavor composition of high-energy astrophysical neutrinos, aiding the analysis of their sources and potential nonstandard flavor mixing effects.

Contribution

It introduces unitarity constraints to establish bounds on astrophysical neutrino flavor composition, considering energy-dependent nonstandard mixing effects.

Findings

Derived unitarity bounds on neutrino flavor ratios.

Applicable to TeV-PeV neutrino energies.

Facilitates analysis of nonstandard flavor mixing.

Abstract

The flavor composition of astrophysical neutrinos observed at neutrino telescopes is related to the initial composition at their sources via oscillation-averaged flavor transitions. If the time evolution of the neutrino flavor states is unitary, the probability of neutrinos changing flavor is solely determined by the unitary mixing matrix that relates the neutrino flavor and propagation eigenstates. In this paper we derive general bounds on the flavor composition of TeV-PeV astrophysical neutrinos based on unitarity constraints. These bounds are useful for studying the flavor composition of high-energy neutrinos, where energy-dependent nonstandard flavor mixing can dominate over the standard mixing observed in accelerator, reactor, and atmospheric neutrino oscillations.