Infrared singularities in QCD amplitudes

Einan Gardi, Lorenzo Magnea

Research output: Contribution to journalArticlepeer-review


We review recent progress in determining the infrared singularity structure of on-shell scattering amplitudes in massless gauge theories. We present a simple ansatz where soft singularities of any scattering amplitude of massless partons, to any loop order, are written as a sum over colour dipoles, governed by the cusp anomalous dimension. We explain how this formula was obtained, as the simplest solution to a newly-derived set of equations constraining the singularity structure to all orders. We emphasize the physical ideas underlying this derivation: the factorization of soft and collinear modes, the special properties of soft gluon interactions, and the notion of the cusp anomaly. Finally, we briefly discuss potential multi-loop contributions going beyond the sum-over-dipoles formula, which cannot be excluded at present.
Translated title of the contributionInfrared singularities in QCD amplitudes
Original languageItalian
Number of pages137
JournalIl Nuovo Cimento C - Colloquia on Physics
Issue number05-06
Early online date24 Aug 2008
Publication statusPublished - 15 Oct 2010


  • hep-ph


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