Implications of Leptonic Unitarity Violation at Neutrino Telescopes

TL;DR

Neutrino telescopes can potentially detect deviations in neutrino flavor ratios caused by non-unitarity in the neutrino mixing matrix, providing a new way to explore physics beyond the Standard Model.

Contribution

This paper demonstrates how ultrahigh-energy neutrino observations can test non-unitarity in the neutrino mixing matrix predicted by seesaw models.

Findings

Flavor ratio deviations up to several percent due to unitarity violation.

Neutrino telescopes can probe new physics beyond the Standard Model.

Method to constrain seesaw model parameters using astrophysical neutrino data.

Abstract

A measurement of the ultrahigh-energy (UHE) cosmic neutrinos at a km^3-size neutrino telescope will open a new window to constrain the 3 x 3 neutrino mixing matrix V and probe possible new physics. We point out that it is in principle possible to examine the non-unitarity of V, which is naturally expected in a class of seesaw models with one or more TeV-scale Majorana neutrinos, by using neutrino telescopes. Considering the UHE neutrinos produced from the decays of charged pions arising from proton-proton and (or) proton-gamma collisions at a distant astrophysical source, we show that their flavor ratios at a terrestrial neutrino telescope may deviate from the democratic flavor distribution \phi^T_e : \phi^T_\mu : \phi^T_\tau = 1 : 1 : 1 due to the seesaw-induced unitarity violation of V. Its effect can be as large as several percent and can serve for an illustration of how sensitive a neutrino telescope should be to this kind of new physics.