The Evolution of Primordial Neutrino Helicities under Gravitational and Magnetic Fields and Implications for their Detection

by Prof. Gordon Baym (University of Illinois at Urbana-Champaign)

Wednesday 26 May 2021, 09:00 → 12:00 Asia/Shanghai

IHEP main building

ABSTRACT: Primordial neutrinos decoupled in the early universe in helicity eigenstates. As I will discuss, two effects -- dependent on neutrinos having a non-zero mass -- can modify their helicities as they propagate through the cosmos. First, finite mass neutrinos have a magnetic moment and thus their spins, but not their momenta, precess in cosmic and galactic magnetic fields. The second is the propagation of neutrinos past cosmic matter density fluctuations, which bend their momenta, and bend their spins to a lesser extent. Both effects turn a fraction of left-handed neutrinos into right-handed neutrinos, and right-handed antineutrinos into left-handed. If neutrino magnetic moments approach even a fraction of that suggested by the XENON1T experiment as a possible explanation of their excess of low energy electron events -- a value well beyond the moment predicted by the standard model -- helicities of relic Dirac (but not Majorana) neutrinos could be considerably randomized. I finally will discuss the implications of neutrino helicity rotation, as well as their Dirac vs. Majorana nature, on their detection rates via the Inverse Tritium Beta Decay reaction. This work is summarized in two papers, G. Baym and J. C. Peng, Phys. Rev. Letters Phys. Rev. Letters 126, 191803 (2021); arXiv:2012.12421v3 [hep-ph]; and arXiv:2103:11209[hep-ph]. About the speaker: Prof. Gordon Baym, studied mathematics and physics at Cornell University, and at Harvard University as a student of Julian Schwinger, receiving his Ph.D. in 1960. He then spent two years at the Institute for Theoretical Physics in Copenhagen (now the Niels Bohr Institute), where he remains a frequent visitor. After a year at Berkeley, he came permanently to the University of Illinois in 1963. His interests in theoretical physics range from quantum statistical mechanics to matter at low temperatures and under extreme conditions. A pioneer in the study of pulsars and neutron stars, he has been a driver in laboratory studies of density matter via ultrarelativistic heavy ion collisions. His ongoing interests include quark matter in neutron stars, the intersection of low temperature and high energy physics in searches for the neutron electron dipole moment and for dark matter, and relic neutrinos from the Big Bang. He is a member of the National Academy of Sciences and of the American Philosophical Society. He was earlier awarded the APS Hans Bethe Prize and the APS Lars Onsager Prize, and the Eugene Feenberg Memorial Medal, and this year the American Physical Society Medal for Exceptional Achievement in Research. His continuing service to the physics community includes recently chairing the National Academy of Sciences study of the Electron-Ion Collider. Zoom Link: https://ihep-ac-cn.zoom.com.cn/j/82100576322?pwd=ei9KUFp5TmdWenR3a1JOK0pFakFkUT09#success Zoon ID: 82100576322 Passed: 918773

Slides neutrinos-BAYM-IHEP.pptx zoom_0.mp4