Multi-Messenger Astrophysics: Synergies Between Cosmic Rays, Gravitational Waves, Neutrinos, and Electromagnetic Signals

Dear Colleagues,

Multi-Messenger Astrophysics is a rapidly developing field for studying high-energy astrophysical objects and phenomena in the universe. Major international projects contribute to multi-messenger observations of cosmic rays, neutrinos, gamma-rays and gravitational waves, connecting thus the fundamental forces, through their different interactions with detectors or media (e.g. outer space, atmosphere, water, ice, Earth). This will lead to progress on open questions on the nature and type of sources of these messengers (e.g. super-massive black holes at the center of active galaxies, violent supernova explosions, or mergers of compact stars in binary systems), on the role of hadronic processes in astrophysical sources, of extra-galactic magnetic fields, and of acceleration and propagation mechanisms. Aspects on the interface to particle physics, such as the nature of hadronic interactions in developing air showers at ultra-high energies also play an important role.

Some recent key results in the field include the measurement of the spectrum of ultra-high energy cosmic rays (UHECRs), upper limits on the diffuse fluxes of photons and neutrinos in the ultra-high energy regime which constrain current models for the origin of UHECRs, the first direct detections of gravitational waves from the merger of binary black holes and binary neutron stars.

This Special Issue aims to provide an overview of the existing and future developments in multi-messenger astrophysics, of theoretical models and the experimental results obtained by space-based and ground-based infrastructures, together with open questions and future  prospects towards next generation multi-messenger observatories. In this context, reviews on theoretical, computational and experimental results, and communications on topical work are highly welcome to provide the community with a comprehensive understanding on the common efforts in the exciting field of multi-messenger astroparticle physics.

Dr. Gina Isar
Prof. Dr. Günter Sigl
Guest Editors

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• cosmic rays and air showers
• high-energy gamma-rays and neutrinos gravitational waves
• acceleration mechanisms and propagation
• cosmic magnetic fields
• cosmic ray anisotropies
• multi-messenger and multi-wavelength signals
• detection methods
• hadronic interaction models
• machine learning and high performance computing