摘要：The QCD axion is a promising dark matter candidate whose cosmological evolution can be altered by a first-order phase transition like that hinted at by the NANOGrav gravitational wave signal. We show such a transition could trigger novel axion dynamics, including mini kinetic misalignment and domain wall formation. This has interesting implications for both the existence of the QCD axion and the FOPT interpretation of the NANOGrav signal. Furthermore, to directly probe the axion dark matter, we propose a novel laboratory search using the ultra-narrow 88 keV Mössbauer transition in Ag-109. The oscillating axion field modulates nuclear energy levels, enabling a sensitive search via precision spectroscopy. This approach already sets leading lab constraints and can probe higher axion masses inaccessible to other methods.
个人简介：Dr. Zhao received his bachelor's degree from Peking University in 2007 and his Ph.D. from Rutgers University in 2012. He then held postdoctoral positions at Stanford University/SLAC and the University of Michigan before joining the University of Utah as a faculty in 2018. In 2025, he moves to HKUST as an associate professor. His research spans a wide range of disciplines, with a particular focus on innovative strategies for searching for dark matter and exploring new physics beyond the Standard Model of particle physics. He also leads the LIGO gravitational wave group at HKUST. As a theorist, he collaborates closely with experimentalists.