Abstract: |
The gravitational-wave memory effect is an unusual prediction of general relativity characterized by an asymptotically constant change in the gravitational-wave strain between early and late times. It produces a measurable effect for freely falling observers (a lasting displacement), it is generated by fluxes of stress-energy and gravitational waves near null infinity, and it is closely related to the symmetry group of asymptotically flat spacetimes, the Bondi-Metzler-Sachs (BMS) group. More recently, the gravitational-wave memory was also understood to be related to Weinberg's soft-graviton theorem, which itself is a consequence of the BMS-invariance of gravitational scattering. New types of gravititational-wave memories have also be proposed that are similarly related to subleading corrections to the soft-graviton theorem and proposed extensions of the BMS algebra. In this talk, I aim to elucidate the other types of physical effects that families of geodesic observers could measure, in principle, after a burst of gravitational waves passes by their locations, and how these are related to the new memories. I also discuss the charges conjugate to these extended BMS algebra elements and their relationship to the new memories. |