摘要：In the Standard Model of particle physics, it is known that the exact conserved charges are the U(1)_Y (or U(1)_EM) and the number difference of baryons and leptons for each generation, B/3-L_f. However, the time-scale of the particle-number-changing interactions, such as the Yukawa interactions, is non-zero, and hence they can be effectively neglected in the early Universe since the time scale of cosmic expansion can be shorter. Therefore, depending on the temperature, there arise more approximate conserved charges, such as the number of right-handed electrons. In particular, at the temperature higher than 10^5 GeV, chiral asymmetry, or the difference of the total right-handed particles and left-handed particles (weighted with U(1)_Y charge), becomes an approximate conserved charge. As a result, phenomena originated from the chiral anomaly, or the chiral effect, can be important. In this talk, I will explain the way how to determine the approximate conserved charges depending on the cosmic temperature, and introduce some phenomena from the chiral effects, such as the magnetic field amplification from the lepton flavor asymmetry or baryogenesis from axion inflation.
个人简介：Kohei Kamada is a distinguished researcher at Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences. He received his Ph.D from the University of Tokyo in 2011 and has worked at Deutsches Elektronen-Synchrotron (DESY), École Polytechnique Fédérale de Lausanne (EPFL), Arizona State University, and Institute for Basic Science as a postdoc. From 2018 to 2023, he has worked at the University of Tokyo as an Assistant Professor before joining HIAS. His research interest centers on the early Universe cosmology and particle phenomenology. His main works include the chiral effects in cosmology, especially their relevance in the cosmological magnetic field and gravitational waves.