I will discuss recent developments in the characterisation of asymptotic states in asymptotically flat gravity, and the central role played by BMS fluxes in connection to soft graviton theorems. As a result of these new ideas, I will show that the subleading soft graviton theorem including loop effects is the Ward identity associated with superrotations symmetries. We will conclude that BMS symmetries are genuine symmetries of the gravitational S-matrix beyond the classical regime.

Email m.godazgar@qmul.ac.uk for zoom link. Abstract: I will present the derivation of the antipodal matching relations used to demonstrate the equivalence between soft graviton theorems and BMS charge conservation across spatial infinity. To this end I will provide a precise map between Bondi data at null infinity and Beig-Schmidt data at spatial infinity in a context appropriate to the gravitational scattering problem and celestial holography. I will also demonstrate that, among various proposals of BMS charges at null infinity found in the literature, only a subset match the conserved charges at spatial infinity and are therefore preferred from that perspective.