# Secondary neutrino and gamma-ray fluxes from SimProp and CRPropa

## TL;DR

This paper compares how different simulation codes and models affect predictions of neutrino and gamma-ray fluxes from ultra-high-energy cosmic rays, highlighting sensitivities and discrepancies in current models.

## Contribution

It provides a detailed comparison of neutrino and gamma-ray flux predictions from CRPropa and SimProp, analyzing the impact of model choices and code updates on these predictions.

## Key findings

- Cosmogenic neutrino fluxes are highly sensitive to EBL model choices.
- Gamma-ray production rates are relatively stable across different propagation models.
- Significant differences exist between predictions of the latest CRPropa and SimProp versions.

## Abstract

The interactions of ultra-high-energy cosmic rays (UHECRs) in extragalactic space with photons of the cosmic microwave background (CMB) and extragalactic background light (EBL) can generate high-energy neutrinos and photons. Simulations of UHECR propagation require knowledge about physical quantities such as the spectrum of the EBL and photodisintegration cross sections. These assumptions, as well as the approximations used in the codes, may influence the computed UHECR spectrum and composition, and the associated cosmogenic neutrino and photon fluxes. Following up on our previous work where we studied the effects of these uncertainties on the UHECR spectrum and composition, here we quantify those on neutrino fluxes and production rates of photons, electrons, and positrons, using the Monte Carlo codes CRPropa and SimProp, in various astrophysical scenarios. We show that cosmogenic neutrinos are more sensitive to the choice of EBL model than UHECRs, whereas the overall cosmogenic gamma-ray production rates are relatively independent of propagation details. We also find significant differences between neutrino fluxes predicted by the latest released versions of CRPropa and SimProp, and discuss their causes and possible improvements in future versions of the codes.