Title: A Forest-based Infrared Subtraction for Wide-angle Scattering
Abstract: For any hard QCD amplitude with massless partons, infrared (IR) singularities arise from pinches in the complex planes of loop momenta, called pinch surfaces. To organize and study their leading behaviors in the neighborhoods of these surfaces, we can construct approximation operators for collinear and soft singularities. In my talk, I will develop a BPHZ-like forest formula to subtract the IR singularities systematically. A related analysis has been carried out by Collins for the back-to-back Sudakov form factors, and is generalized here to any wide-angle kinematics with an arbitrary number of external momenta. After a brief introduction to Minkowskian IR divergences in momentum space, I will first illustrate that the approximations yield much richer IR structures than those of an original amplitude, then construct the forest formula and prove that all the singularities appearing in its subtraction terms cancel pairwise. Finally, with the help of this forest formula, the full amplitude can be reorganized into a factorized expression. (Password to access the Video recording: 6b$B37x3)