Soft gravity by squaring soft QED on the celestial sphere

We recast the soft S matrices on the celestial sphere as correlation functions of certain two-dimensional models of topological defects. In pointing out the double-copy structure between the soft photon and soft graviton cases, we arrive at a putative classical double copy between the corresponding topological models and a rederivation of gauge invariance and the equivalence principle as Ward identities of the two-dimensional theories.

Automated summary

The authors reinterpret the soft S matrices as correlation functions of certain two-dimensional models of topological defects and point out the double-copy structure between the soft photon and soft graviton cases. They propose a putative classical double copy between the corresponding topological models and rederive gauge invariance and the equivalence principle as Ward identities of the two-dimensional theories.