Describing the Observed Cosmic Neutrinos by Interactions of Nuclei with Matter

TL;DR

This paper models the spectral shape and flavor composition of cosmic neutrinos observed by IceCube, exploring how source properties and nuclear composition influence observed features and proposing upgrades for future analysis.

Contribution

It introduces a simple model linking neutrino spectra and flavor composition to source parameters and nuclear composition, highlighting the potential to test UHECR acceleration mechanisms.

Findings

Soft spectra or magnetic fields can produce PeV cutoffs.

Heavier nuclei can explain observations if maximal energy scales with mass.

Flavor information can serve as a key discriminator in future IceCube upgrades.

Abstract

IceCube have observed neutrinos which are presumably of extra-galactic origin. Since specific sources have not yet been identified, we discuss what could be learned from the conceptual point of view. We use a simple model for neutrino production from the interactions between nuclei and matter, and we focus on the description of the spectral shape and flavor composition observed by IceCube. Our main parameters are spectral index, maximal energy, magnetic field, and composition of the accelerated nuclei. We show that a cutoff at PeV energies can be achieved by soft enough spectra, a cutoff of the primary energy, or strong enough magnetic fields. These options, however, are difficult to reconcile with the hypothesis that these neutrinos originate from the same sources as the ultra-high energy cosmic rays. We demonstrate that heavier nuclei accelerated in the sources may be a possible way out if the maximal energy scales appropriately with the mass number of the nuclei. In this scenario, neutrino observations can actually be used to test the UHECR acceleration mechanism. We also emphasize the need for a volume upgrade of the IceCube detector for future precision physics, for which the flavor information becomes a statistical meaningful model discriminator as qualitatively new ingredient.