Asymptotic symmetry algebra of Einstein gravity and Lorentz generators

Abstract

The asymptotic symmetry algebra of four-dimensional Einstein gravity in the asymptotically flat context has been shown recently to be the direct sum of the Poincaré algebra and of an infinite-dimensional abelian algebra (with central charge) that includes the Bondi-Metzner-Sachs supertranslations. This result, obtained within the Hamiltonian formalism, yields a supertranslation invariant definition of the Lorentz generators (angular momentum and boosts). Definitions of Lorentz generators free from the ``supertranslation ambiguities'' have also been proposed recently at null infinity. We prove the equivalence of the two approaches for redefining the charges.