Seminar: Pulsar Polarization Array and Its First Limits on Ultralight Axion-like Dark Matter

ABSTRACT

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 and fundamental physics through a common correlated polarization signal at galaxy scales. In this talk, the speaker will introduce this innovative methodology and discuss one of its scientific applications: detecting ultralight axion-like wave dark matter (ALDM). The speaker will present the first limits from the PPA on the ALDM Chern-Simons coupling with the electromagnetic field, obtained in collaboration with the Parkes PTA collaboration using polarization data from 22 millisecond pulsars from its third data release. In the mass region of "Fuzzy Dark Matter,'' the speaker will demonstrate that this analysis provides the best global limits in the "standard'' context. the speaker will also highlight the role of pulsar cross-correlation in understanding the nature of the derived limits. Finally, the speaker will briefly discuss the future applications of the PPA and its potential synergy with the PTA.

References:

(1) https://journals.aps.org/prd/abstract/10.1103/PhysRevD.101.063012

(2) https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.130.121401

(3) "First Pulsar Polarization Array Limits on Ultralight Axion-like Dark Matter '', under review for publication.

BIOGRAPHY

Prof. Tao Liu's research focuses on particle physics and its connections to astronomy and cosmology. He earned his PhD in Physics from the University of Pennsylvania in 2007. Following this, he held the position of "McCormick Fellow'' at the Enrico Fermi Institute at the University of Chicago from 2007 to 2010. He then moved to the University of California, Santa Barbara, to continue his postdoctoral research. In 2013, Prof. Liu joined the Hong Kong University of Science and Technology (HKUST) as a junior faculty member and is now a full professor. He received the HKUST "School of Science Research Award'' in 2016. Currently, he serves as Principal Coordinator for the Hong Kong UGC/RGC Collaborative-Research-Fund project titled "Dark Matter and the Universe.''