Double Soft Graviton Theorems and BMS Symmetries

TL;DR

This paper demonstrates that nested Ward identities from BMS charges lead to double soft graviton theorems, connecting asymptotic symmetries with complex scattering amplitude behaviors.

Contribution

It introduces a novel approach linking nested BMS Ward identities to double soft graviton theorems, expanding the understanding of asymptotic symmetries in gravity.

Findings

Double soft graviton theorems derived from nested Ward identities.

At sub-leading order, these theorems match consecutive double soft graviton results.

Nested Ward identities relate to BMS symmetries in non-Fock vacua.

Abstract

It is now well understood that Ward identities associated to the (extended) BMS algebra are equivalent to single soft graviton theorems. In this work, we show that if we consider nested Ward identities constructed out of two BMS charges, a class of double soft factorization theorems can be recovered. By making connections with earlier works in the literature, we argue that at the sub-leading order, these double soft graviton theorems are the so-called consecutive double soft graviton theorems. We also show how these nested Ward identities can be understood as Ward identities associated to BMS symmetries in scattering states defined around (non-Fock) vacua parametrized by supertranslations or superrotations.