Open Questions in Cosmic-Ray Research at Ultrahigh Energies

• Published in: Frontiers in astronomy and space sciences Vol. 6
• Main Authors: Alves Batista, Rafael, Biteau, Jonathan, Bustamante, Mauricio, Dolag, Klaus, Engel, Ralph, Fang, Ke, Kampert, Karl-Heinz, Kostunin, Dmitriy, Mostafa, Miguel, Murase, Kohta, Oikonomou, Foteini, Olinto, Angela V., Panasyuk, Mikhail I., Sigl, Guenter, Taylor, Andrew M., Unger, Michael
• Format: Journal Article
• Language: English
• Published: Frontiers Media 04.06.2019; Frontiers Media S.A
• Subjects: Astrophysics; extensive air shower detectors; hadronic interactions; intergalactic magnetic fields; mass composition; Physics; ultrahigh energy cosmic rays; ultrahigh energy neutrinos; new physics; Mass composition of cosmic rays; extrensive-air-shower detectors; cosmic radiation: spectrum; anisotropy; Intergalactic magnetic field; magnetic field: effect; trajectory; Ultrahigh energy cosmic rays; ultrahigh energy neutrinos; ultrahigh-energy-cosmic-ray anisotropy; mass spectrum; gamma ray; hadronic interactions at ultrahigh energies; cosmic radiation: UHE; neutrino; neutral particle; galaxy
• ISSN: 2296-987X; 2296-987X
• DOI: 10.3389/fspas.2019.00023

We review open questions and prospects for progress in ultrahigh-energy cosmicray (UHECR) research, based on a series of discussions that took place during the “The High-Energy Universe: Gamma-Ray, Neutrino, and Cosmic-ray Astronomy” MIAPP workshop in 2018.Specifically, we overview open questions on the origin of the bulk of UHECRs, the UHECR mass composition, the origin of the end of the cosmic-ray spectrum, the transition from Galactic to extragalactic cosmic-rays, the effect of magnetic fields on thetrajectories of UHECRs, anisotropy expectations for specific astrophysical scenarios, hadronicinteractions, and prospects for discovering neutral particles as well as new physics at ultrahighenergies. We also briefly overview upcoming and proposed UHECR experiments and discusstheir projected science reach.