Advanced Studies in Ultra-High-Energy Cosmic Rays

Dear Colleagues,

Ultra-high-energy cosmic rays (UHECRs) are the most energetic, rare and mysterious particles in the Universe. They are either charged or neutral particles, such as light to heavy nuclei, or photons and neutrinos. Galactic and intergalactic magnetic fields are deflecting the charged particles in their way of travel to the Earth, making it hard to identifying their cosmic source from their arrival direction.

It has been extensively reported in the literature that UHECRs are of extragalactic origin, but their punctual source it remains a mystery for scientists nowadays. Furthermore, the flux of the UHECRs drops dramatically with increasing energy, below one particle per square km per year above 10¹⁸ eV, and below one particle per square km per century above 10²⁰ eV, making their study a challenge.

In the first decade of the 21st century, the field has thus undergone a true phase transition, both in terms of size and of data quality, with the advent of extensive hybrid observatories such as the Pierre Auger Observatory in the southern hemisphere, and soon after the Telescope Array in the northern hemisphere, providing a wealth of new observations, but also new questions about the nature and origin of UHECRs.

The large-scale experiments are currently being upgraded in order to answer these new questions, yet promoting the field to another era, by looking for the developing air showers with improved or hybrid surface particle detectors and fluorescence telescope. Measuring various species of cosmic rays with different detection techniques defines the new domain of Multi-messenger Astronomy, where charged cosmic rays, neutral particles, and gravitational waves, play together an important role at the frontier of the Nuclear Physics, Astrophysics, Astronomy and Cosmology, the so-called Astroparticle Physics. Additionally, a huge effort is put on modeling the development of cosmic ray showers in different media, as well as on the propagation of cosmic rays in the galactic and intergalactic space through magnetic fields, diluted media and radiations.

Within this Special Issue, we would like to highlight the latest analysis results obtained in the field of UHECRs, in frame of complementary studies on the multi-messenger observations of cosmic ray particles, with the focus on their origin and nature, studying their arrival direction and primary particle type identification, their interaction at the highest energies, global fits constraining astrophysical models and new physics, as well as innovative detection techniques.

Dr. Gina Isar
Prof. Dr. François Montanet
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Universe is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

• cosmic rays
• air showers
• neutral particles
• hadronic interactions
• production processes
• emission mechanisms
• detection techniques
• Monte Carlo simulations