Ultra-high neutrino fluxes as a probe for non-standard physics

TL;DR

This paper explores how ultra-high energy neutrinos from distant sources can be used to detect non-standard physics phenomena like neutrino decay and Lorentz violation by analyzing spectral distortions across neutrino flavors.

Contribution

It introduces a method to use spectral differences in neutrino flavors from distant sources as indicators of exotic physics, expanding the parameter space for such phenomena.

Findings

Spectral distortions can signal non-standard physics effects.

Standard oscillations produce similar flavor spectra at Earth.

Detectable differences in flavor spectra are possible with current detectors.

Abstract

We examine how light neutrinos coming from distant active galactic nuclei (AGN) and similar high energy sources may be used as tools to probe non-standard physics. In particular we discuss how studying the energy spectra of each neutrino flavour coming from such distant sources and their distortion relative to each other may serve as pointers to exotic physics such as neutrino decay, Lorentz symmetry violation, pseudo-Dirac effects, CP and CPT violation and quantum decoherence. This allows us to probe hitherto unexplored ranges of parameters for the above cases, for example lifetimes in the range $ 10^{-3}-10^{4} $ s/eV for the case of neutrino decay. We show that standard neutrino oscillations ensure that the different flavours arrive at the earth with similar shapes even if their flavour spectra at source may differ strongly in both shape and magnitude. As a result, observed differences between the spectra of various flavours at the detector would be signatures of non-standard physics altering neutrino fluxes during propagation rather than those arising during their production at source. Since detection of ultra-high energy (UHE) neutrinos is perhaps imminent, it is possible that such differences in spectral shapes will be tested in neutrino detectors in the near future. To that end, using the IceCube detector as an example, we show how our results translate to observable shower and muon-track event rates.