The three-loop cusp anomalous dimension in QCD

Understand

We present the full analytic result for the three-loop angle-dependent cusp anomalous dimension in QCD.

• With this result, infrared divergences of planar scattering processes with massive particles can be predicted to that order.
• Moreover, we define a closely related quantity in terms of an effective coupling defined by the light-like cusp anomalous dimension.
• We find evidence that this quantity is universal for any gauge theory, and use this observation to predict the non-planar $n_{f}$-dependent terms of the four-loop cusp anomalous dimension.