Non-abelian infrared divergences on the celestial sphere
by
U1-01
University of Milan Bicocca
The fact that infrared divergences are long-distance effects has recently been formulated in a new language, involving asymptotic symmetries of scattering amplitudes on the `celestial sphere' intersecting the light-cone at infinite time. Using this technology, I will consider the infrared factorisation of non-abelian multi-particle scattering amplitudes, mostly focusing on colour-dipole contributions, and I will show that the infrared factor has a remarkably simple expression in celestial coordinates, with scale and coupling dependence factorised from kinematics and colour. Generalising earlier suggestions in the abelian theory, I will then show that the infrared factor can be computed as a correlator of vertex operators in a conformal field theory of Lie-algebra-valued free bosons on the celestial sphere. The same conformal theory correctly predicts the all-order structure of collinear limits, and the tree-level factorisation of soft real radiation.