On May 11, 2026, the [NanGaoShi·Physics Lecture] series hosted by the School of Physical Science and Technology at Nanjing Normal University was held in Room 435 of the Xingjian Building. Professor Xiao-Gang He, Chair Professor at the Tsung-Dao Lee Institute and a renowned theoretical physicist, was invited to visit the School and deliver an academic lecture entitled “From Particle Flavor to the Origin of the Universe” for faculty members and students. The lecture was chaired by Professor Lei Wu of the School of Physics, and was attended by faculty members and graduate students from related disciplines.

In his lecture, Professor He began with the Standard Model of elementary particles and the standard cosmological model, focusing on the role of flavor physics in quarks, leptons, neutrinos, the Higgs boson, and the gauge particles that mediate interactions. He also discussed the challenges associated with CP violation, the search for new physics, and prospects for recent breakthroughs. The lecture first addressed the question of what flavor physics is, introducing the classification of elementary particles in the Standard Model, their interactions, and the mechanism by which masses are generated. Professor He emphasized that flavor physics is not the isolated study of a single type of particle; rather, it provides a way to understand the overall structure of the Standard Model through masses, mixing, decays, and interactions. Topics such as the Higgs mechanism, parity violation, electroweak unification, and the strong interaction together demonstrate that flavor physics forms an important bridge connecting particle properties, interaction laws, and experimental observations.

Professor He also highlighted CP violation and the search for signals of new physics. The lecture discussed the CKM matrix, B-meson decays, lepton flavor physics, neutrino oscillations, and related topics, showing that although the Standard Model has been remarkably successful, it still faces pressure from a number of precision tests. For example, tests of CKM unitarity, the RK and RD anomalies in B decays, the muon g-2, the W-boson mass, and certain measurements of CP violation have shown, or continue to show, deviations from Standard Model predictions. Some of these anomalies have weakened as new data have become available, while others remain worthy of sustained attention. The lecture therefore emphasized that more experimental data and higher-precision theoretical calculations are needed to determine whether these phenomena are statistical fluctuations, theoretical uncertainties, or genuine signals of new physics beyond the Standard Model.

In the final part of the lecture, Professor He extended flavor physics to questions concerning the origin of the Universe. He introduced topics including the thermal history of the early Universe, the cosmic microwave background, Big Bang nucleosynthesis, the cosmic neutrino background, dark matter, dark energy, and baryon asymmetry, pointing out that particle flavor may have a profound impact on cosmic evolution. The fact that matter greatly exceeds antimatter in the Universe requires the Sakharov conditions: baryon number violation, C and CP violation, and departure from thermal equilibrium. Although the Standard Model contains these ingredients, its CP violation and phase-transition strength are insufficient to explain the observed baryon asymmetry, making new physics necessary. Leptogenesis, the seesaw model, dark matter candidates, and rare decays all illustrate the close connection between flavor physics and the origin of the Universe. During the discussion session, participating faculty members and students engaged in in-depth exchanges and lively discussions with Professor He on frontier topics in flavor physics and cosmology. The lecture not only broadened the academic horizons of the participants, but also laid a solid foundation for future interdisciplinary theoretical collaboration.

About the Speaker:

Xiao-Gang He is Chair Professor at the Tsung-Dao Lee Institute of Shanghai Jiao Tong University and Director of its Division of Particle and Nuclear Physics. He previously served as a Distinguished Professor in the Department of Physics at National Taiwan University and as Director of the Physics Division of the National Center for Theoretical Sciences in Taiwan. He is a Fellow of the American Physical Society. He received his bachelors degree from the University of Science and Technology of China as a member of the class of 1977. In 1981, he was selected for the China-U.S. Physics Examination and Application program (CUSPEA), initiated and promoted by Professor Tsung-Dao Lee. He went to the University of Hawaii in 1982 and received his Ph.D. in 1987. Professor He has long been engaged in particle physics research. His research areas include quantum topological phases, including the discovery of the He-McKellar-Wilkens topological quantum phase; electroweak and strong interactions; new physics beyond the Standard Model; and cosmology. His major contributions include proposing the type-III neutrino seesaw model and independently proposing tri-bimaximal mixing; identifying the importance of electroweak penguin diagrams in B physics and CP violation studies; predicting experimentally verified relations among different B decay processes; and proposing criteria for testing the Higgs-portal dark matter mechanism as well as leptophilic dark matter models. He has published more than 350 academic papers, with over 16,000 citations, more than 1,300 citations for his most-cited single paper, and an h-index of 64.