NBIA Seminar: Kohta Murase

New frontiers of particle astrophysics have been opened by IceCube's discovery of high-energy cosmic neutrinos. Their origin is a new mystery in the field, and solving this problem may enable us not only to understand the physics of astrophysical sources but also to obtain important clues about old mystery, the origin of cosmic rays, and to utilize neutrinos as probes of neutrino properties, dark matter, and fundamental physics. In this talk, I will review basic ideas on the origin of high-energy cosmic neutrinos. I will first discuss cosmic-ray "reservoir" models, which predicted fluxes and spectra consistent with the IceCube data, and emphasize the grand-unified model we recently proposed. On the other hand, I will argue that they cannot explain the data below 100 TeV, and suggest hidden cosmic-ray accelerators.