The high-energy cosmic neutrinos discovered by the IceCube neutrino telescope have vast potential to test new, extreme regimes of particle physics and astrophysics. They have the highest known neutrino energies---up to a few PeV (= 10^15 eV)---and travel the longest distances---up to a few Gigaparsecs, the size of the observable Universe. These features make them attractive probes of particle-physics properties, possibly tiny in size and at energy scales unreachable by other means, and of the conditions inside the most energetic astrophysical sources. The decades before the IceCube discovery saw many proposals of studies in these directions. Today, these proposals have become a reality. I will showcase examples of testing neutrino physics at these scales, including stringent tests of physics beyond the Standard Model, and of constraining the physical conditions in the astrophysical neutrino sources. For the next decade, the prospects are thrilling: after fifty years of waiting, we may finally discover long-sought neutrinos with energies thousands of times higher, thanks to an ambitious experimental program.
Mauricio Bustamante is an Assistant Professor at the Niels Bohr Institute of the University of Copenhagen, Denmark. He got his PhD from the University of Würzburg and DESY. He followed that, first, with a postdoc at the Center for Cosmology and Astroparticle Physics (CCAPP) at The Ohio State University, and then a postdoc at the Niels Bohr Institute. His primary interest is testing neutrino physics at the highest energies, looking for signs of physics beyond the Standard Model, and improving strategies to search for them. In addition, he is involved in a number of efforts planning the next generation of high-energy neutrino telescopes.