Abstract: Gravitational memory effects are permanent and cumulative shifts of relative observables (distance, velocity, angular momentum ...) between two test particles induced by the passage of a gravitational wave. They stand as one of the last prediction of general relativity (GR) yet to be confirmed through the gravitational wave astronomy. In turn, they are intimately related to the notion of degeneracy of the vacuum in gauge theory and important efforts have been devoted to characterize these effects through the relation to the symmetries of spacetime. In this talk, I will consider the simplest exact non-linear radiative solution of GR, namely a vacuum gravitational plane wave, and show step by step how to classify the different memory effects occurring in this case. I will show new relation between memories and hidden symmetries (Killing tensors), and resolve conflicting claim in the literature regarding the possibility to have displacement or velocity memory effects. The goal is to illustrate a concrete method based on symmetries and applicable to more complex radiative spacetime, in particular asymptotically flat radiative spacetimes.   

Based on : https://arxiv.org/abs/2406.07106