The present white paper is submitted as part of the “Snowmass” process to help inform the
long-term plans of the United States Department of Energy and the National Science …

Active Galactic Nuclei (AGNs) and their relativistic jets belong to the most promising class of
ultra-high-energy cosmic ray (UHECR) accelerators. This compact review summarises basic …

In this work we present the interpretation of the energy spectrum and mass composition data
as measured by the Pierre Auger Collaboration above 6× 1017 eV. We use an astrophysical …

K-EUSO (KLYPVE-EUSO) is a planned orbital mission aimed at studying ultra-high energy
cosmic rays (UHECRs) by detecting fluorescence and Cherenkov light emitted by extensive …

We report an estimation of the injected mass composition of ultrahigh energy cosmic rays
(UHECRs) at energies higher than 10 EeV. The composition is inferred from an energy …

Interactions of ultra-high-energy cosmic rays (UHECRs) in the surroundings of their
accelerators can naturally explain the observed spectrum and composition of UHECRs …

To take up the challenge of understanding the origin of the ultra-high-energy cosmic rays
(UHECRs), new observational means appear necessary. The JEM-EUSO Collaboration has …

I review the status of ultrahigh-energy cosmic ray (UHECR) physics. After introducing the
main experimental results and summarizing possible intepretations, I discuss observational …

Here, we point out that an observation of ultrahigh energy cosmic ray (UHECR)
photons,“GZK photons”, could provide an upper limit on the level of the extragalactic radio …

The development of multimessenger astrophysics allows us to probe various background
particles from the distant early universe. Up to now, much effort has been made researching …