学术报告 报告题目1：Bondi-Sachs Spacetimes and Gravitational Waves
报 告 人：张晓 教授（中国科学院）
报告时间：2017年05月31日（星期三）上午09:30-10:30
报告题目2：Flag varieties and quantum symmetric pairs
报 告 人：樊赵兵 教授（哈尔滨工程大学）
报告时间：2017年05月31日（星期三）上午10:40-11:40
报告地点：4号楼4131室
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数学学院
2017年05月30日
报告1摘要： Bondi-Sachs spacetimes describe the nonlinear effect of gravitational waves. In the zero cosmological constant, they were originally introduced by Bondi for axi-symmetric spacetimes, and generalized by Sachs to general asymptotically flat spacetimes over 50 years ago. Bondi also defined the Bondi energy-momentum at null infinity, the physical conserved quantity which represents the rest energy of spacetimes after the loss duo to gravitational radiation.
1998’s cosmological observation indicated that our universe has a positive cosmological constant. On February 11, 2016, gravitational waves, modeling from a pair of zero cosmological constant’s merging black holes, was first observed using the Advanced LIGO detectors. Since then, the Bondi-Sachs spacetimes with positive cosmological constant gain much attention by physicists.
In this talk, we shall discuss the solutions of basic questions arisen in gravitational waves for zero cosmological constant. Whether the Bondi energy is nonnegative, i.e., whether the gravitational waves can carry away more energy than they initially have? How the Bondi energy-momentum relates to the ADM energy-momentum defined at spatial infinity? We shall also discuss the natural boundary condition including gravitational waves for the Bondi-Sachs spacetimes in the case of nonzero cosmological constant, and the surprising peeling property for this boundary condition.
报告2摘要：By using flag varieties, one can establish a duality between Hecke algebras of different types and some coideal algebras of quantum groups of (affine) type A. The duality is a generalization of quantum Schur-Weyl duality. Those coideal algebras and quantum groups of (affine) type A form quantum symmetric pairs.