Cosmic ray interactions with matter and radiation

TL;DR

This paper reviews key particle interactions and energy loss mechanisms affecting high-energy cosmic rays in the Galactic medium, highlighting their role in shaping spectra and producing secondary particles used in multi-messenger astrophysics.

Contribution

It provides a comprehensive overview of cosmic ray interactions at ultra-high energies, complementing existing lectures and focusing on processes in the extragalactic environment.

Findings

Detailed description of particle interactions and energy loss mechanisms.

Explanation of secondary particle production like gamma rays and neutrinos.

Contextualization within multi-messenger astrophysics.

Abstract

The main goal of the present lectures is to outline the key particle interactions and energy loss mechanisms in the Galactic medium that high-energy particles are subject to. These interactions are an important ingredient entering the cosmic ray propagation equation, contributing to shape cosmic ray spectra. They also source the so-called secondary species, like gamma rays, neutrinos, "fragile" nuclei not synthesised in stars, and antiparticles, all routinely used as diagnostic tools in a multi-messenger context. These lectures are complementary to Denise Boncioli's ones, focusing instead on processes happening at ultra-high energies in the extragalactic environment. They include propaedeutic material to Felix Aharonian's and, to some extent, Stefano Gabici's and Carmelo Evoli's lectures.