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arXiv · 0908.3273

Infrared singularities in QCD amplitudes

Einan Gardi·Lorenzo Magnea
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Abstract

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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Einan Gardi, Lorenzo Magnea. 2009-08-24. Infrared singularities in QCD amplitudes. https://doi.org/10.1393/ncc%2Fi2010-10528-x

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