A New Topological Symmetry of Asymptotically Flat Spacetimes

Abstract: I will show that the isometry group of asymptotically flat spacetimes contains, in addition to the BMS group, a new dual supertranslation symmetry. The corresponding new conserved charges are akin to the large magnetic U(1) charges in QED. They factorize the Hilbert space of asymptotic states into distinct super-selection sectors and reveal a rich topological structure exhibited by the asymptotic metric. I will describe this structure and some resulting applications, including the construction of a gravitational-magnetic monopole solution analogous to the Wu-Yang monopole and a new gravitational duality akin to electric-magnetic duality.