演講資訊

摘要：

Despite being associated with massless particles, electromagnetic and gravitational waves do not propagate strictly on the null cone in curved spacetimes. They also develop tails, traveling inside the light cone. This tail effect, in particular, provides a contribution to the self-force of compact bodies orbiting super-massive black holes, which in turn are believed to be important sources of gravitational waves for future space based detectors like LISA, TianQin and Taiji. For the first portion of my talk I will describe my efforts to explore novel methods to understand the tail effect in curved geometries -- primarily in cosmological spacetimes. Some of the spin-offs include the (small) discovery of new type of gravitational wave memory effect induced by tails. If time permits, for the second part of my talk, I will address a seemingly basic aspect of gravitational wave theory that -- as far as I am aware -- has not received proper clarification in the literature to date. Specifically, the "transverse-traceless" gravitational wave (GW) is usually touted as the gauge-invariant observable; while practical computations actually do not strictly yield this "TT" GW. Furthermore, the gauge-invariant TT GW is actually acausally related to its matter source, as can be seen by simply computing its associated Green's function. I will clarify the situation for the spin-1 photon, as an analogy to the gravitational case.