Asymptotic symmetries and subleading soft graviton theorem

TL;DR

This paper introduces an extended BMS group incorporating Diff(S^2) and demonstrates that its Ward identities correspond to the subleading soft graviton theorem, deepening the understanding of asymptotic symmetries in gravity.

Contribution

It proposes a new extension of the BMS group involving Diff(S^2) and links its Ward identities to the subleading soft graviton theorem.

Findings

Extended BMS group with Diff(S^2) is proposed.

Ward identities match the subleading soft graviton theorem.

Defines canonical generators for smooth diffeomorphisms.

Abstract

Motivated by the equivalence between soft graviton theorem and Ward identities for the supertranslation symmetries belonging to the BMS group, we propose a new extension (different from the so-called extended BMS) of the BMS group which is a semi-direct product of supertranslations and Diff(S^2). We propose a definition for the canonical generators associated to the smooth diffeomorphisms and show that the resulting Ward identities are equivalent to the subleading soft graviton theorem of Cachazo and Strominger.