Particle and Astrophysics Aspects of Ultrahigh Energy Cosmic Rays

TL;DR

This paper reviews the origins, theoretical explanations, and experimental efforts related to ultrahigh energy cosmic rays, highlighting their potential to probe fundamental physics and early Universe conditions.

Contribution

It provides a comprehensive overview of current theories, experimental developments, and the use of cosmic rays as probes of large-scale magnetic fields and early Universe phenomena.

Findings

Charged ultrahigh energy cosmic rays can probe large-scale magnetic fields.

Experimental advancements will increase data at highest energies.

Monte Carlo simulations help understand cosmic ray propagation and origins.

Abstract

The origin of cosmic rays is one of the major unresolved astrophysical questions. In particular, the highest energy cosmic rays observed possess macroscopic energies and their origin is likely to be associated with the most energetic processes in the Universe. Their existence triggered a flurry of theoretical explanations ranging from conventional shock acceleration to particle physics beyond the Standard Model and processes taking place at the earliest moments of our Universe. Furthermore, many new experimental activities promise a strong increase of statistics at the highest energies and a combination with $\gamma-$ray and neutrino astrophysics will put strong constraints on these theoretical models. Detailed Monte Carlo simulations indicate that charged ultra-high energy cosmic rays can also be used as probes of large scale magnetic fields whose origin may open another window into the very early Universe. We give an overview over this quickly evolving research field.