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Infrared singularities in QCD amplitudes

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arxiv 0908.3273 v1 pith:HNLR6ILE submitted 2009-08-24 hep-ph

classification hep-ph
keywords softamplitudescuspformulainfraredmasslessscatteringsingularities
verification ladder T0 review T1 audit T2 compute T3 formal

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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.

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Cited by 12 Pith papers

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