Self-confinement of ultra-high-energy nuclei in cosmic filaments: implications for the UHECR spectrum and composition

TL;DR

This paper explores how self-generated magnetic turbulence in cosmic filaments can confine ultra-high-energy nuclei, affecting their spectrum and composition, and aligns these predictions with observational data and neutrino/gamma-ray constraints.

Contribution

It extends the self-confinement model to mixed nuclear compositions and assesses its impact on UHECR spectrum, composition, and associated neutrino and gamma-ray emissions.

Findings

Self-generated turbulence can suppress UHECR flux below the EV scale.

Heavy nuclei undergo photodisintegration producing secondary protons.

Predicted neutrino flux is compatible with current observational limits.

Abstract

The spectrum and composition of ultra-high-energy cosmic rays (UHECRs) suggest that the population dominating above the ankle releases particles with an unusual hard spectrum at low rigidity, below the EV scale. In self-confinement scenarios, such an apparent hardening arises from transport: escaping UHECRs generate magnetic turbulence that delays their own release from the magnetized environments surrounding their sources. We extend the self-confinement scenario based on the non-resonant streaming instability to a mixed nuclear composition. We describe the confinement region with an effective leaky-box model including escape, photodisintegration, and secondary production. We then compare the resulting spectrum and composition with Auger measurements and compute the associated cosmogenic neutrino and gamma-ray emission. We find that self-generated turbulence can suppress the escaping flux below the EV scale for source luminosities and magnetic-field coherence lengths compatible with UHECR sources hosted in galaxy clusters and propagating through cosmic filaments. During confinement, heavy nuclei efficiently photodisintegrate, producing secondary protons that contribute below the ankle and help account for the observed composition. The predicted neutrino flux remains compatible with current limits, while the diffuse gamma-ray background provides a potentially strong constraint on the most extreme configurations.