Burg-Metzner-Sachs symmetry, string theory, and soft theorems

We study the action of the Burg-Metzner-Sachs (BMS) group in critical, bosonic string theory living on a target space of the form M super(d) xC. Here M super(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.