报告题目：On the polarization of gravitational waves in alternative theories of gravity
报告时间：2018-04-23 15:30 (星期一)
报告地点：天津大学北洋园校区32楼B256
报告人：龚云贵 教授（华中科技大学）

报告摘要

According to the Newman-Penrose formalism, in general there are sixpolarizations for general theories of gravity. In particular, the presence ofthe longitudinal mode means that the theory has all six polarizations. Formassive scalar-tensor theory of gravity or f(R) theory, the longitudinal modepresents, but the theory has only three dynamical degrees of freedom, it seemsthat there is inconsistency somewhere. We point out that the Newman-Penroseformalism is not directly applicable to massive mode, the polarization of themassive scalar field is a mix of breathing and longitudinal mode and the longitudinalmode is proportional to the mass, when the mass becomes zero, the mix modebecomes the pure breathing mode which is consistent with the Newman-Penroseformalism. Since the longitudinal mode is proportional to the mass, so it canbe detected only in very low frequency band, like the PTA band. The result isfundamentally important for the understanding of the nature of gravity. If weonly detect the plus and cross polarizations, then we know that graviton ismassless spin 2 particle. In addition to the plus and cross polarizations, ifwe also detect the breathing polarization, then we know that gravitation ismediated by both massless spin 2 and spin 0 particles. Apart from the abovethree polarizations, if we also detect the longitudinal polarization, then weknow that gravitation propagated by massless spin 2 and massive spin 0particles.

报告人简历： 龚云贵，华中科技大学二级教授、博士生导师，美国贝勒大学客座教授。1991年毕业于原华中理工大学（现华中科技大学）并获得学士学位，1994年在中国科学院理论物理研究所获得硕士学位，2001年获得美国德克萨斯州立大学奥斯汀分校博士,师从SU(3)理论创始者之一、美国科学院院士Neeman教授。在PRL等国际高水平学术期刊上发表了100多篇SCI学术论文，发表的学术论文在高能数据库Spires中被引用3900余次，其中10篇论文被引用超过100次，h指数为34。主持了包括国家自然科学基金重点项目在内的多项国家及省部级科研项目。国际广义相对论和引力学会终身会员，亚太物理学会天体物理、引力和宇宙学分会执委，中国引力与相对论天体物理学会秘书长，湖北省物理学会常务理事。先后荣获教育部新世纪优秀人才计划、中国侨界双百贡献奖（创新人才奖）、重庆市自然科学一等奖。现主要从事相对论引力与宇宙学的研究工作。