Effects of uncertainties in simulations of extragalactic UHECR propagation, using CRPropa and SimProp

TL;DR

This paper assesses how uncertainties in physical models and simulation codes affect the predicted spectrum and composition of extragalactic ultra-high energy cosmic rays, highlighting the impact of EBL and photodisintegration models.

Contribution

It systematically compares the effects of different models and codes on UHECR propagation simulations, providing insights into the sources of uncertainties.

Findings

EBL model choice significantly impacts UHECR spectrum.

Photodisintegration setup influences composition predictions.

Differences between CRPropa and SimProp affect simulation outcomes.

Abstract

The results of simulations of the extragalactic propagation of ultra-high energy cosmic rays (UHECRs) have intrinsic uncertainties due to poorly known physical quantities and approximations used in the codes. We quantify the uncertainties in the simulated UHECR spectrum and composition due to different models for the extragalactic background light (EBL), different photodisintegration setups, approximations concerning photopion production and the use of different simulation codes. We discuss the results for several representative source scenarios with proton, nitrogen or iron at injection. For this purpose we used SimProp and CRPropa, two publicly available codes for Monte Carlo simulations of UHECR propagation. CRPropa is a detailed and extensive simulation code, while SimProp aims to achieve acceptable results using a simpler code. We show that especially the choices for the EBL model and the photodisintegration setup can have a considerable impact on the simulated UHECR spectrum and composition.