Double Copy for Celestial Amplitudes

Celestial amplitudes which use conformal primary wave functions rather than plane waves as external states offer a novel opportunity to study properties of amplitudes with manifest conformal covariance and give insight into a potential holographic celestial conformal field theory at the null boundary of asymptotically flat space. Since translation invariance is obscured in the conformal basis, features of amplitudes that heavily rely on it appear to be lost. Among these are the remarkable relations between gauge theory and gravity amplitudes known as the double copy. Nevertheless, properties of amplitudes reflecting fundamental aspects of the perturbative regime of quantum field theory are expected to survive a change of basis. Here we show that there exists a well-defined procedure for a celestial double copy. This requires a generalization of the usual squaring of numerators which entails first promoting them to generalized differential operators acting on external wave functions and then squaring them. We demonstrate this procedure for three- and four-point celestial amplitudes and give an argument for its validity to all multiplicities.

Twistorial Foundation for the Classical Double Copy

The classical double copy relates exact solutions of gauge, gravity, and other theories. Although widely studied, its origins and domain of applicability have remained mysterious. In this Letter, I show that a particular incarnation-the Weyl double copy-can be derived using well-established ideas from twistor theory. As well as explaining where the Weyl double copy comes from, the twistor formalism also shows that it is more general than previously thought.