Flavors of Astrophysical Neutrinos with Active-Sterile Mixing

TL;DR

This paper derives analytical bounds on the flavor composition of high-energy astrophysical neutrinos considering active-sterile mixing, extending previous three-flavor bounds without relying on specific parameter values.

Contribution

It provides unitarity-based analytical bounds on astrophysical neutrino flavor composition in scenarios with active-sterile mixing, applicable across various energy-dependent models.

Findings

Bounds are analytical and parameter-independent.

Applicable to energy-dependent active-sterile mixing scenarios.

Extends previous three-flavor mixing bounds to include sterile neutrinos.

Abstract

We revisit the flavor composition of high-energy astrophysical neutrinos observed at neutrino telescopes. Assuming unitary time evolution of the neutrino flavor states, the flavor composition observable at Earth is related to the initial composition at their sources via oscillation-averaged flavor transitions. In a previous study we derived general bounds on the flavor composition of TeV-PeV astrophysical neutrinos assuming three-flavor unitary mixing. We extend these bounds to the case of active-sterile neutrino mixing. Our bounds are analytical, derived based only on the unitarity of the mixing, and do not require sampling over the values of the unknown active-sterile mixing parameters. These bounds apply to any extended active-sterile neutrino mixing scenario where energy-dependent nonstandard flavor mixing dominates over the standard mixing observed in accelerator, reactor, and atmospheric neutrino oscillations.