Perturbative scattering on strong backgrounds

In perturbative quantum field theory, the S-matrix is the observable encoding the probabilities for scattering processes to occur between specified asymptotic states. Recent advances (often based upon twistor and ambitwistor theory) have determined the full semi-classical S-matrix for a wide variety of massless field theories, perturbatively around a trivial background. However, very little is known about the S-matrix perturbatively around non-trivial, or strong, background fields, despite myriad physical scenarios where this is important.
Recently, it was shown that many powerful tools from the trivial background also apply in strong backgrounds: for instance, the full non-linear equations of motion and the spectrum of free fields coupled to the background are encoded by ambitwistor strings, and there are hints that the powerful double copy relationship between gauge theory and gravity also holds in strong backgrounds. This project will explore applications of twistor theory, ambitwistor theory and (ambi)twistor string theory to the study of scattering in strong backgrounds for gauge theory, gravity and other QFTs. Specific targets include: the S-matrix and its analogues on self-dual backgrounds; the S-matrix on a generic plane wave background; the formulation of double copy in strong backgrounds; and the development of a twistorial scattering formalism for black hole space-times.