"The PeV Frontier "
Three quite different research investigations are making discoveries at TeV-PeV energies that point to new astrophysical sources and, possibly, new physics. The first involves gamma-ray observations extending up to several PeV using a variety of techniques. The second is the realization that the spectrum of cosmic rays at roughly PeV energy is measured to be much greater and to have a different nuclear composition than seems to be achievable by the supernova remnant shock fronts responsible for lower energy particles. The third is the detection of cosmic neutrino sources, again with energies up to a few PeV, and possibly much more. (The neutrino discoveries have been acknowledged by the 2026 Nobel Prize in Physics.) In this lecture I will summarize candidate explanations for these sources ranging from known entities > involving black holes, neutron stars and shock fronts, which may demonstrate that Nature is cleverer > than we are, through to exciting and exotic explanations for which there is no other evidence. The options for expanding the frontier to EeV and > ZeV energy, as already probed by observation of > Ultra High Energy Cosmic Rays, will be briefly reviewed.
