# Probing the Extragalactic Cosmic Rays origin with gamma-ray and neutrino backgrounds

## TL;DR

This paper investigates the origins of extragalactic ultra-high-energy cosmic rays using gamma-ray and neutrino backgrounds, analyzing recent Fermi-LAT and IceCube data to constrain source models and predict future detection prospects.

## Contribution

It demonstrates that a mixed-composition UHECR model aligns with current gamma-ray and neutrino observations and explores future detection possibilities for cosmogenic neutrinos.

## Key findings

- Mixed-composition UHECR model consistent with Fermi-LAT and IceCube data.
- Constraints on UHECR source evolution derived from gamma-ray and neutrino fluxes.
- Future experiments could detect cosmogenic neutrinos to further test UHECR models.

## Abstract

GeV-TeV gamma-rays and PeV-EeV neutrino backgrounds provide a unique window on the nature of the ultra-high-energy cosmic-rays (UHECRs). We discuss the implications of the recent Fermi-LAT data regarding the extragalactic gamma-ray background (EGB) and related estimates of the contribution of point sources as well as IceCube neutrino data on the origin of the UHECRs. We calculate the diffuse flux of cosmogenic $\gamma$-rays and neutrinos produced by the UHECRs and derive constraints on the possible cosmological evolution of UHECR sources. In particular, we show that the mixed-composition scenario considered in \citet{Globus2015b}, which is in agreement with both (i) Auger measurements of the energy spectrum and composition up to the highest energies and (ii) the ankle-like feature in the light component detected by KASCADE-Grande, is compatible with both the Fermi-LAT measurements and with current IceCube limits. We also discuss the possibility for future experiments to detect associated cosmogenic neutrinos and further constrain the UHECR models, including possible subdominant UHECR proton sources.