INTERNATIONAL SCHOOL ON NONEQUILIBRIUM PHENOMENA: 6th Course: Astroparticle Physics, Dark Matter and High Energy Physics

At high and very high energies, astronomy and astroparticle physics come to a crossroads, as the same few powerful cosmic sources that emit over the whole electromagnetic spectrum up to GeV and TeV energies are also sites of particle acceleration to ultra-relativistic speeds, far beyond those that can be attained in any man-built accelerator. In order to make critical progress on the knowledge and understanding of these sources, it is essential to study comparatively their multi-messenger information provided by instrumentation sensitive to their electromagnetic (radio, optical and Cherenkov telescopes on the ground, X- and gamma-ray satellites) and non-electromagnetic signals (cosmic rays, MeV to PeV neutrinos). In these same energy regimes may sit also the elusive constituents of dark matter, that are still covered by a thick blanket of mystery. After its advent in the '60s, with the detection of solar neutrinos, multi-messenger astrophysics underwent a spectacular revival in 1987, when thermal MeV neutrinos were detected from SN1987A - the incontrovertible proof of massive stellar core collapse to a neutron star - and again in the past decade, when gravitational waves were directly observed following binary compact star coalescences, starting in 2015, and high-energy (>100 TeV) neutrinos outbursts were detected simultaneously with multi-wavelength electromagnetic flares of active galactic nuclei, starting in 2017, suggesting that these sources may be responsible for cosmic particles acceleration beyond PeV energies. The aim of this Course is to review the main observational facts and evidence about the connection between astrophysical and astroparticle phenomenology provided by the state-of-the-art (MAGIC, HESS, LHAASO, AUGER) and soon-to-come (CTAO, KM3NET) experiments, and their underpinning physical principles and theory: acceleration mechanisms, dark matter nature and behavior, and neutrino physics.