Theory seminar (11am): Rayan Haindl: Local subtraction for 3-loop QCD corrections to EW-production in q\bar{q}-annihilation using IR-universality

Thursday 3 Apr 2025, 11:00 → 12:00 Europe/Amsterdam

Veltman Centre (Nikhef)

Loop amplitudes with multiple kinematic or mass scales are notoriously difficult to compute. I discuss a local subtraction framework for QCD corrections to electroweak production in quark-antiquark annihilation up to three-loop order. Ward identities ensure the factorisation of most collinear singularities from the hard-scattering process in the sum over integrands. In this framework, infrared singularities are removed point-by-point in loop momentum space using a small set of analytically calculable “form-factor” counterterms (CTs), while the finite remainder is amenable to numerical integration. Additional CTs eliminate non-factorising terms arising from loop momentum shifts and one-loop corrections to the gluon three-point function. Finally, I identify previously unknown non-factorising “loop polarisation” effects in the single-collinear regions, which pose challenges for local integrability and require further investigation. The techniques presented here are a first crucial step in formulating a systematic approach for constructing finite integrands for general electroweak amplitudes at three-loop order.