Propagation of high-energy cosmic rays in extragalactic turbulent magnetic fields: resulting energy spectrum and composition

TL;DR

This paper investigates how extragalactic turbulent magnetic fields influence the energy spectrum and composition of high-energy cosmic rays, introducing a fast trajectory integration method that refines spectrum predictions.

Contribution

It presents a novel fast integration method for cosmic-ray trajectories in turbulent magnetic fields, enabling more accurate spectrum and composition modeling without simplifying assumptions.

Findings

Magnetic fields below a few nG do not significantly alter model features.

The transition from ballistic to diffusive propagation is characterized.

Key spectral features remain stable under certain magnetic field strengths.

Abstract

We extend previous studies of mixed-composition extragalactic cosmic-ray source models, by investigating the influence of a non-negligible extragalactic magnetic field on the propagated cosmic-ray spectrum and composition. We study the transport of charged particles in turbulent fields and the transition from a ballistic to a diffusive propagation regime. We introduce a method allowing a fast integration of the particle trajectories, which allows us to calculate extragalactic cosmic-ray spectra in the general case, without using either the diffusive or the rectilinear approximation. We find that the main features of the mixed-composition models -- regarding the interpretation of the ankle and the non-monotonous evolution of the average cosmic-ray mass -- remain essentially unchanged as long as the magnetic field intensity does not exceed a few nG.