Exploring neutrino loss with diffuse astrophysical neutrino fluxes

TL;DR

This paper investigates how the diffuse astrophysical neutrino flux observed by IceCube can constrain new physics effects like neutrino decay or interactions, despite source uncertainties.

Contribution

It introduces a method to constrain neutrino loss effects using energy conservation and IceCube data, accounting for source distribution and energy dependence.

Findings

Severely constrains neutrino loss beyond existing bounds.

Shows energy-dependent attenuation can influence flux spectral index.

Quantifies bounds through fitting IceCube's High-Energy Starting Events.

Abstract

We study the sensitivity of the diffuse high-energy neutrino flux observed in IceCube to new-physics effects resulting in an exponential flux attenuation along the trajectory, such as invisible neutrino decay or new interactions with the background encountered during propagation. We argue that, even though the sources and production redshifts of these astrophysical neutrinos are unknown, conservative energy-conservation arguments allow to severely constrain neutrino loss in most scenarios beyond the strongest existing bounds. By performing a fit to the High-Energy Starting Events from IceCube, we quantify the bounds and study their variation with the energy dependence of the attenuation, the assumed redshift distribution of the neutrino sources, and whether the attenuation affects neutrinos exclusively or no. We also show that including an energy-dependent attenuation at the level allowed in the fit may impact the determination of the spectral index of the diffuse flux.