Pseudo-Dirac Neutrinos and Relic Neutrino Matter Effect on the High-energy Neutrino Flavor Composition

TL;DR

This paper explores how pseudo-Dirac neutrinos and the cosmic neutrino background can influence high-energy neutrino flavor ratios observed on Earth, proposing a novel matter effect detectable by future telescopes.

Contribution

It introduces a new matter effect caused by the cosmic neutrino background on pseudo-Dirac neutrino oscillations, affecting flavor ratios in high-energy astrophysical neutrinos.

Findings

Energy-dependent flavor ratios due to CνB matter effect

Next-generation detectors can test the pseudo-Dirac neutrino hypothesis

Potential to distinguish matter effects from vacuum oscillations

Abstract

We show that if neutrinos are pseudo-Dirac, they can potentially affect the flavor ratio predictions for the high-energy astrophysical neutrino flux observed by IceCube. In this context, we point out a novel matter effect induced by the cosmic neutrino background (C$\nu$B) on the flavor ratio composition. Specifically, the active-sterile neutrino oscillations over the astrophysical baseline lead to an energy-dependent flavor ratio at Earth due to the C$\nu$B matter effect, which is in principle distinguishable from the vacuum oscillation effect, provided there is an asymmetry between the neutrino and antineutrino number densities, as well as a local C$\nu$B overdensity. Considering the projected precision of the 3-neutrino oscillation parameter measurements and improved flavor triangle measurements, we show that the next-generation neutrino telescopes, such as KM3NeT and IceCube-Gen2, can in principle probe the pseudo-Dirac neutrino hypothesis and the C$\nu$B matter effect.