Computing the soft anomalous dimensions with both massive and massless particles

by Zehao Zhu (University of Edinburgh)

Wednesday 21 Jan 2026, 13:15 → 14:15 Europe/Berlin

Soft singularities of scattering amplitudes are important for both theoretical and practical reasons. It is well known that these singularities are captured by correlators of Wilson lines which follow the classical trajectory of energetic partons participating in the process and intersect at the hard interaction vertex. Such correlators feature ultraviolet singularities, which allow us to compute the soft anomalous dimension, provided the infrared is regularized. However, while correlators of time-like Wilson lines which intersect each other are multiplicatively renormalizable, strictly light-like Wilson lines feature also collinear singularities and lose multiplicative renormalizability. This feature complicates their regularization and the separation between infrared and ultraviolet singularities. Indeed, the soft anomalous dimensions of massless scattering amplitudes are rather different from that of massive ones, and the relation between them is subtle. 

In this talk, I will start from the standard method of computing the soft anomalous dimensions with all particles massive. Then, I will turn to a new strategy developed for calculating infrared singularities with both heavy and  light particles. This strategy is based on the method of regions which is used to perform the asymptotic expansion of Feynman integrals at the integrand level. By using the method of regions, we are able to make use of the multiplicative renormalizability as well as lightlike kinematics. Finally, I will discuss a new result — the one-mass soft anomalous dimension at three loops — obtained using the new strategy.