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Abstract: First-order phase transitions in hidden gauge sectors can generate stochastic gravitational wave backgrounds, providing a powerful new probe of dark sector physics. In this talk, I will present a gauge-independent analysis of gravitational waves from a minimal dark U(1) sector containing a dark Higgs and a dark photon, with the possible inclusion of a vectorlike dark fermion as a dark matter candidate. Particular emphasis will be placed on low-temperature phase transitions. By combining the Nielsen identity with a controlled derivative expansion and gauge coupling power-counting framework, one can construct a gauge-independent effective action in both the high-temperature and low-temperature regimes. This allows for robust predictions of bubble nucleation dynamics and the resulting gravitational wave signals. The results show that low-temperature phase transitions generally produce stronger and more readily detectable gravitational wave signals. Our analysis provides a reliable and concrete prediction framework for gravitational waves from the minimal U(1) dark sector.
Biography: Dr. Wan-Zhe Feng is a tenured Associate Professor at the School of Science, Tianjin University. He received his B.S. degree in physics from Peking University and his Ph.D. degree in theoretical physics from Northeastern University in the United States. He subsequently held postdoctoral positions at the Department of Physics and the Institute for Advanced Study at the Hong Kong University of Science and Technology, the Max Planck Institute for Physics in Munich, and the Arnold Sommerfeld Center for Theoretical Physics at Ludwig Maximilian University of Munich. He also held a visiting scientist position at Northeastern University. Dr. Feng joined Tianjin University in November 2018.
Following his early research in string theory during his Ph.D. and postdoctoral period, Dr. Feng shifted his focus to particle physics phenomenology, with particular emphasis on dark matter and dark sector dynamics. His research has covered low-energy supersymmetry, the origin of the matter-antimatter asymmetry, Higgs physics, flavor physics, and neutrino physics. His recent work focuses on the role of dark sector dynamics in the cosmological evolution of dark matter, as well as gravitational waves from cosmological phase transitions.
Online Link: Join Zoom Meeting
https://umass-amherst.zoom.us/j/9432601370?pwd=V0d6dVUzT3NXaGxvWDBhekdhOFk5UT09&omn=93787572123
Meeting ID: 943 260 1370
Passcode: Saguaro