Collinear factorisation breaking and loop-tree duality: a tribute to Stefano Catani

by German Rodrigo (IFIC CSIC-UV)

Monday 29 Apr 2024, 14:00 → 16:00 Europe/Zurich

4/S-030 (CERN)

I will discuss two topics where the pioneering ideas of Stefano Catani have played a central role, and where important and relevant developments have been made recently. Collinear factorization is a fundamental assumption in theoretical predictions at high-energy colliders. However, strict collinear factorization can be broken for certain kinematic configurations starting from one-loop in scattering amplitudes, and at N3LO for jet production at hadron colliders. We present the generalisation of collinear factorisation to configurations with several collinear directions that appear at higher orders, where the most singular behaviour is encoded by generalised collinear splitting amplitudes that manifestly embed the breaking of strict collinear factorisation. We also extend the analysis to the simultaneous soft-collinear factorisation with multiple collinear directions. With regard to the second topic, we introduce the LTD causal unitary method, which exploits the manifestly causal properties of vacuum amplitudes in the loop-tree duality (LTD) to provide a novel representation of differential observables at high-energy colliders that is locally free of infrared, ultraviolet and threshold singularities and thus well defined in the four physical dimensions of the space-time.

2024_04_CERN_rodrigo.pdf