BMS supertranslations and Weinberg’s soft graviton theorem
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Recently it was conjectured that a certain infinite-dimensional “diagonal” subgroup of BMS supertranslations acting on past and future null infinity ( Open image in new window and Open image in new window ) is an exact symmetry of the quantum gravity S-matrix, and an associated Ward identity was derived. In this paper we show that this supertranslation Ward identity is precisely equivalent to Weinberg’s soft graviton theorem. Along the way we construct the canonical generators of supertranslations at Open image in new window , including the relevant soft graviton contributions. Boundary conditions at the past and future of Open image in new window and a correspondingly modified Dirac bracket are required. The soft gravitons enter as boundary modes and are manifestly the Goldstone bosons of spontaneously broken supertranslation invariance.
KeywordsScattering Amplitudes Space-Time Symmetries
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