BMS, String Theory, and Soft Theorems

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.