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QCD Lunch

Non-abelian infrared divergences on the celestial sphere

by Lorenzo Magnea (Universita e INFN Torino (IT))

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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.


on-line via ZOOM