HET seminar: Einan Gardi – University of Copenhagen

HET seminar: Einan Gardi

Speaker: Einan Gardi

Title: Recent progress on 
long-distance singularities in QCD amplitudes


I describe the state-of-the-art knowledge of long-distance singularities in QCD scattering amplitudes. These singularities are encoded, to all orders, in the so-called soft anomalous dimension. This quantity was computed a couple of years ago to three-loop order by evaluating the relevant set of Feynman diagrams. More recently, its functional form was recovered using a bootstrap approach, constraining an ansatz using symmetries and special kinematic limits. 
After briefly reviewing the factorisation and exponentiation properties of soft singularities, I outline the main considerations employed in the two approaches used to compute the soft anomalous dimension. Finally, I discuss the interplay between the study of soft singularities and that of amplitudes in special kinematic limits, such as the high-energy limit, or the collinear limit, where different factorisation properties apply.