PeV neutrinos from the propagation of ultra-high energy cosmic rays

TL;DR

This paper investigates the origins of PeV neutrinos observed by IceCube, analyzing how extragalactic cosmic ray interactions with various radiation backgrounds produce neutrino fluxes, and discusses implications for detection and composition scenarios.

Contribution

It provides a detailed analysis of neutrino production mechanisms during cosmic ray propagation, highlighting the dominant processes and the impact of cosmic ray composition on fluxes.

Findings

Pion decay interactions with UV/optical/IR backgrounds dominate PeV neutrino production.

Neutron decay from cosmic ray interactions is significantly suppressed.

Mixed composition scenarios can enhance PeV neutrino fluxes.

Abstract

We discuss the possibility that the PeV neutrinos recently observed by IceCube are produced by the interactions of extragalactic cosmic rays during their propagation through the radiation backgrounds. We show that the fluxes resulting from the decays of neutrons produced in the interactions of cosmic ray protons with the CMB background are suppressed ($E_\nu^2$d$\Phi_\nu/$d$E< 10^{-10}$ GeV/cm$^2$ s sr), with those resulting from the decays of pions produced in the interactions with the UV/optical/IR backgrounds being the dominant ones at PeV energies. The anti-neutrino fluxes produced by the decay of neutrons resulting from the photodisintegration of heavy nuclei with CMB photons are also shown to be quite suppressed ($E_\nu^2$d$\Phi_\nu/$d$E< 10^{-11}$ GeV/cm$^2$ s sr), while those produced by photo-pion processes with UV/optical/IR backgrounds may be larger, although they are not expected to be above those achievable in the pure proton case. Scenarios with mixed composition and low cutoff rigidities can lead to PeV neutrino fluxes enhanced with respect to those in the pure Fe scenarios. We also discuss the possible impact of the Glashow resonance for the detection of these scenarios, showing that it plays a moderate role.