(Peer-Reviewed) Covariant phase space with null boundaries
Kai Shi ¹, Xuan Wang ¹, Yihong Xiu ¹, Hongbao Zhang 张宏宝 ¹ ²
¹ Department of Physics, Beijing Normal University, Beijing 100875, China
中国 北京 北京师范大学物理学系
² Theoretische Natuurkunde, Vrije Universiteit Brussel, and The International Solvay Institutes, Pleinlaan 2, B-1050 Brussels, Belgium
Abstract
By imposing the boundary condition associated with the boundary structure of the null boundaries rather than the usual one, we find for Einstein's gravity that the variational principle works only in its submanifold with the null boundaries given by the expansion-free and shear-free hypersurfaces rather than in the whole covariant phase space.
This implies that the key requirement in Harlow–Wu's algorithm for the timelike boundaries is too restrictive for the null ones. To incorporate more generic situations into Harlow–Wu's algorithm, we relax such a requirement. As a result, we successfully reproduce the Hamiltonian obtained previously by Wald–Zoupas' prescription for Einstein's gravity.
A review on optical torques: from engineered light fields to objects
Tao He, Jingyao Zhang, Din Ping Tsai, Junxiao Zhou, Haiyang Huang, Weicheng Yi, Zeyong Wei Yan Zu, Qinghua Song, Zhanshan Wang, Cheng-Wei Qiu, Yuzhi Shi, Xinbin Cheng
Opto-Electronic Science
2025-11-25
