Probe Of Sterile Neutrinos Using Astrophysical Neutrino Flavor

TL;DR

This paper investigates how active-sterile neutrino mixing affects the flavor composition of high-energy astrophysical neutrinos, proposing new visualization tools and analyzing the potential to detect sterile neutrinos through flavor measurements.

Contribution

It introduces the four-flavor tetrahedron to visualize non-unitarity and explores how sterile neutrinos influence astrophysical neutrino flavor ratios.

Findings

Active-sterile mixing modifies flavor ratio regions.

Initial sterile neutrinos significantly alter flavor space.

Flavor measurements can probe sterile neutrinos independently of their mass.

Abstract

In this paper, we study the effect of active-neutrino-sterile-neutrino mixing in the expected high-energy astrophysical neutrino flavor content. Non-unitarity in the measurement of the three active neutrinos can be due to the existence of sterile neutrino states. We introduce the concept of the four-flavor tetrahedron in order to visualize the lack of unitarity in the astrophysical neutrino three-flavor triangle. We demonstrate that active-sterile neutrino mixings modify the allowed region of the astrophysical flavor ratio from the standard case. However, a projection of the four-flavor tetrahedron has restrictions of phase space similar to the three-flavor triangle. On the other hand, the initial presence of astrophysical sterile neutrinos drastically changes the scenario, and it allows an apparent unitarity violation in the three-flavor triangle space. Using current global fit constraints including the non-unitarity case, we also illustrate the allowed astrophysical neutrino flavor ratios. Thus, the measurement of the high-energy astrophyscal neutrino flavor content allows us to explore sterile neutrinos independently of the sterile neutrino mass scale. These are topics of investigation for current and future neutrino telescopes.