New thoughts on old gauge amplitudes

Abstract: I will discuss recent work in collaboration with Kevin Costello. We propose a new formula for computing form factors of a four-dimensional theory, which in turn are related to certain scattering amplitudes of gluons in QCD. These formulas are given in terms of correlation functions of a 2d chiral algebra. The chiral algebra that appears is closely related to one appearing in the celestial holography program. We explain the connection between the 4d amplitudes and 2d correlation functions via a 6d holomorphic theory on twistor space. Along the way, we show that the celestial chiral algebra of pure self-dual gauge theory, with states of both helicities, fails to be associative at loop-level.