BMS, String Theory, and Soft Theorems

TL;DR

This paper explores how BMS symmetries in string theory relate to soft theorems, deriving boundary conditions and transformations in higher dimensions, and connecting Ward identities to Weinberg's soft theorem.

Contribution

It provides a string theory derivation of BMS transformations and Ward identities in higher dimensions, linking them to soft theorems.

Findings

BMS group acts on string theory in higher dimensions.

Generalized Ward--Takahashi identities are derived from string theory.

BMS Ward identities reproduce Weinberg's soft theorem in string theory.

Abstract

We study the action of the BMS group in critical, bosonic string theory living on a target space of the form $\mathbb{M}^{d}\times C$. Here $M^{d}$ is $d$-dimensional (asymptotically) flat spacetime and $C$ is an arbitrary compactification. We provide a treatment of generalized Ward--Takahashi identities and derive consistent boundary conditions for any $d$ from string theory considerations. Finally, we derive BMS transformations in higher dimensional spacetimes and show that the generalized Ward--Takahashi identity of BMS produces Weinberg's soft theorem in string theory.