报告题目：Background-Induced Forces from Quadratically Coupled Ultralight Dark Matter

报 告 人：Hailin Xu 徐海麟 (Tsung-Dao Lee Institute)

报告时间：2026年9月24日 14：00

报告地点：物理楼W260会议室

内容摘要：Quadratically coupled ultralight scalar dark matter behaves as a coherent classical field whose interactions with matter can induce a composition-dependent force through the dark matter background. We present a complete calculation of this background-induced force beyond the spherically symmetric approximation. Using a partial-wave treatment of dark-matter scattering, we determine its angular dependence and derive an analytic description valid even when the dark-matter wavelength is much smaller than the Earth's radius. We show for the first time that Earth screening generates a characteristic frequency-band structure, splitting the signal into multiple sidebands that provide a distinctive experimental signature. We further show that the relative amplitudes of these sidebands vary annually due to the Earth's motion through the dark-matter halo, enabling the construction of a complete signal template. As an application of these results, we re-evaluate constraints from the MICROSCOPE mission, which currently provides the strongest laboratory limits on equivalence-principle violations from ultralight dark matter. We further show that proposed space-based equivalence-principle experiments, such as Galileo Galilei and STE-QUEST, can significantly enhance their sensitivity to ultralight scalar dark matter by incorporating the full frequency-band information.

报告人简介： Hailin Xu is a postdoctoral researcher in the Particle and Nuclear Physics Division, Tsung-Dao Lee Institute. He works in theoretical particle physics, including astrophysical and cosmological probes for dark matter, direct and indirect detection of dark matter, and physics beyond the Standard Model.