Prof. Mu-chun Chen, University of California, Irvine

"Neutrinos and Physics beyond the Standard Model"

Coffee and cookies will be served at 3:45pm in RLM 4.102

Abstract: Neutrino, having several Nobel Prizes in Physics directly under its belt, including 2015's Prize for the discovery of neutrino mass by the Super-Kamiokande and Sudbury Neutrino Observatory Collaborations, is the most elusive and, besides photon, the most abundant particle in the Universe. On the other hand, there are still many outstanding questions about the neutrinos that are yet to be answered. While we now know that the Higgs particle gives masses to all charged elementary fermions, we still have no clue what generates the neutrino masses. Furthermore, we don't know at the fundamental level what causes neutrinos to morph from one type to another while traveling through space, and whether the time reversal symmetry is broken in neutrino oscillation. Neutrinos also play a very important role in cosmology. While the Cosmic Microwave Background takes us all the way back to 380,000 years after the Big Bang, the standard Cosmic Neutrino Background, if ever observed, will take us all the way back to the very first second after the Big Bang! In addition, neutrinos may be responsible for the generation of the matter-antimatter asymmetry in the Universe.

In this talk, I will briefly review the current state of neutrino physics. I will discuss possible new physics, based on symmetry principle, that can naturally give rise to small neutrino masses and their oscillation pattern. Because of the symmetry, there exist predictions that allow for the theory to be tested at current and upcoming experiments. I will present a novel mechanism for the violation of time reversal symmetry, which is one of the necessary conditions for generating dynamically the matter-antimatter asymmetry in the Universe. Finally, I will elucidate a tantalizing possibility of the existence of a non-standard Cosmic Neutrino Background, enabled if neutrinos are Dirac fermions, that would provide a novel window into the very early Universe.