Subleading soft photons and large gauge transformations

TL;DR

This paper links subleading soft photon theorems in massless QED to Ward identities of large gauge transformations, providing a new perspective that could extend to gravity's sub-subleading theorems.

Contribution

It introduces a class of large U(1) gauge transformations with computable charges, connecting their Ward identities to Low's soft photon theorem, offering a novel approach.

Findings

Charges from large gauge transformations can be computed from first principles.

Ward identities of these charges are equivalent to Low's theorem.

Framework suggests potential extension to gravitational sub-subleading theorems.

Abstract

Lysov, Pasterski and Strominger have shown how Low's subleading soft photon theorem can be understood as Ward identities of new symmetries of massless QED. In this paper we offer a different perspective and show that there exists a class of large $U(1)$ gauge transformations such that (i) the associated (electric and magnetic) charges can be computed from first principles (ii) their Ward identities are equivalent to Low's theorem. Our framework paves the way to analyze the sub-subleading theorem in gravity in terms of Ward identities associated to large diffeomorphisms.