报告题目：Unveiling Ultralight Axion-like Dark Matter — A PTA-PPA Method

报  告 人：Tao Liu professor, Hong Kong University of Science and Technology(HKUST)

研究方向：Particle physics and cosmology

报告时间：2025年10月9日（星期四）下午16:00

报告地点：量子楼410报告厅

报告摘要：

Pulsars are remarkable astronomical clocks and linear polarizers. As astronomical clocks, the millisecond pulsars can be used to form an astronomical interferometer, known as Pulsar Timing Array (PTA) since 1980's, to detect nano-Hertz gravitational waves. As linear polarizers, the speaker and his collaborators have proposed recently to construct Pulsar Polarization Array (PPA) to explore new phenomena in astrophysics through a common correlated polarization signal on galaxy scales [1,2]. In this talk, the speaker will introduce these innovative tools and discuss how the PPA, together with the PTA, can be applied for detecting ultralight axion-like dark matter (ALDM). The speaker will present the first limits from the PPA on the ALDM Chern-Simons coupling with photons, obtained in collaboration with the Parkes PTA collaboration using polarization data from 22 millisecond pulsars from its third data release [3], and expand the study to the PTA detection of the ALDM, based on the analysis of Fermi-LAT gamma-ray data [4]. In particular, the speaker will highlight the role of pulsar cross-correlation in recognizing the nature of the derived limits. At last, the speaker will introduce the PTA - PPA synergy in this task [5], and discuss the directions for next-step explorations.

References:

[1] Phys.Rev.D 101 (2020) 6, 063012

[2] Phys.Rev.Lett. 130 (2023) 12, 121401

[3] e-Print: 2412.02229 [astro-ph.HE]

[4] Astrophys.J.Lett. 963 (2024) 2, L46

[5] e-Print: 2506.04871 [astro-ph.CO]

报告人简介：

Dr. Tao Liu's research focuses on particle physics and its connections to astronomy and cosmology. Dr. Liu earned his PhD in Physics from the University of Pennsylvania in 2007. He served as a McCormick Fellow at the Enrico Fermi Institute at the University of Chicago from 2007 to 2010, and then moved to the University of California, Santa Barbara, to continue his postdoctoral research. In 2013, Dr. Liu joined the Hong Kong University of Science and Technology (HKUST) as a junior faculty member and is now a full professor. Notable community contributions of Dr. Liu include acting as Principal Coordinator for the Hong Kong UGC/RGC Collaborative Research Fund project titled ``Dark Matter and the Universe'', co-leading the preparation of the CEPC documents on physics.