Double Soft Graviton Theorems and BMS Symmetries

Understand

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.