Seminar link:http://myumi.ch/O4P7E

Celestial amplitudes which use conformal primary wavefunctions 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 CFT at the null boundary of asymptotically flat space. With the notion of energy traded for the conformal dimension under the Lorentz group acting on the celestial sphere, energetically soft theorems of QFT scattering amplitudes are replaced by "conformally soft" theorems. Moreover, since translation invariance is obscured in the conformal basis, features of amplitudes that heavily rely on it, such as the remarkable relations between gauge theory and gravity amplitudes known as the double copy, appear to be lost. My main focus in this talk is to show that there exists nevertheless a well-defined procedure for a celestial double copy. This requires a generalization of the usual squaring of numerators to first promoting them to generalized differential operators acting on external wavefunctions, and then squaring them. I will end with recent results on how to obtain celestial loop amplitudes from tree level ones.