The Asymptotic Structure of Gravity at Spatial Infinity in Four Spacetime Dimensions

A review of our results on the asymptotic structure of gravity at spatial infinity in four spacetime dimensions is given. Finiteness of the action and integrability of the asymptotic Lorentz boost generators are key criteria that we implement through appropriate boundary conditions. These conditions are “twisted parity conditions,” expressing that the leading order of the asymptotic fields obeys strict parity conditions under the sphere antipodal map up to an improper gauge transformation. The asymptotic symmetries are shown to form the infinite-dimensional Bondi–Metzner–Sachs group, which has a nontrivial action. The charges and their algebra are worked out. The presentation aims at being self-contained and at possessing a pedagogical component.