Four-loop angle-dependent cusp anomalous dimension in QED

by Kai Yan

Friday 13 Nov 2020, 10:00 → 12:00 Europe/Zurich

CERN

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Angle-dependent cusp anomalous dimension governs the divergences coming from soft gluon exchanges between massive particles. We compute matter-dependent quartic Casimir component, the first truly non-planar contribution. Our result sheds new light on the infrared structure of gauge-theory amplitudes at generic cusp angle. On the one hand, it interpolates between various physically interesting kinematic limits in both maximally supersymmetric gauge theory (N=4 sYM), and QCD. On the other hand, it constitutes the first quantum correction beyond propagator-type diagrams in the abelian theory.

Obtaining an analytic four-loop prediction, with exact kinematic dependence, is beyond the state of the art of most approaches. To overcome various technical difficulties, we developed an algorithm for solving system of differential equations, based only on partial knowledge of the canonical basis. We demonstrate its applicability and usefulness to a large-scale problem, and in particular, systems of quasi-finite integrals.

Cusp.pdf