报告题目:Gravitational memory effects and Bondi-Metzner-Sachs symmetries in scalar-tensor theories

报告人：侯绍齐

报告时间：10月27日10:00—11:00

报告地点：理学楼A110

题目(Title)：Gravitational memory effects and Bondi-Metzner-Sachs symmetries in scalar-tensor theories

摘要(Abstarct): The relation between gravitational memory effects and Bondi-Metzner-Sachs symmetries of the asymptotically flat spacetimes is studied in the scalar-tensor theory. For this purpose, the solutions to the equations of motion near the future null infinity are obtained in the generalized Bondi-Sachs coordinates with a suitable determinant condition. It turns out that the Bondi-Metzner-Sachs group is also a semi-direct product of an infinite dimensional supertranslation group and the Lorentz group as in general relativity. There are also degenerate vacua in both the tensor and the scalar sectors in the scalar-tensor theory. The supertranslation relates the vacua in the tensor sector, while in the scalar sector, it is the Lorentz transformation that transforms the vacua to each other. So there are the tensor memory effects similar to the ones in general relativity, and the scalar memory effect, which is new. The evolution equations for the Bondi mass and angular momentum aspects suggest that the null energy fluxes and the angular momentum fluxes across the null infinity induce the transition among the vacua in the tensor and the scalar sectors, respectively. With the Wald-Zoupas formalism, ``conserved charges'' and fluxes of the Bondi-Metzner-Sachs algebra are computed. The scalar degree of freedom contributes only to the Lorentz boost charge, although it plays a role in various fluxes. The flux-balance laws are further applied to constrain displacement memory and spin memory effects.

地点(Room)：理学楼 A110

时间(Time)： 10:00 - 11:00 am,  Oct. 27, 2020 (Tuesday)

报告人(Bio)： 侯绍齐，武汉大学物理与科学技术学院博士后。于2006年至2010年就读于山东大学，获物理学理学学士学位；于2010年至2016年就读于美国亚拉巴马大学，获物理学博士学位。2016年12月至2018年11月，在华中科技大学任博士后；2018年12月至今，在武汉大学任博士后。研究课题为利用引力波偏振检验修改引力理论，和引力波透镜效应以及标准汽笛的研究。

Shaoqi Hou is currently a post-doctoral in Wuhan University. He got the Bachelor’s Degree in Physics from Shandong University in 2010. He obtained his Ph.D. in Physics from The University of Alabama in 2016. From Dec. 2016 to Nov. 2018, he worked in Huazhong University of Science and Technology as a post-doctoral. From Dec. 2018 to the present, he has been working as a post-doctoral in Wuhan University. He is interested in the polarization of the gravitational wave and its application to examine modified theories of gravity  and the gravitational lensing of the gravitational wave and the standard siren.