Subtracting Infrared Singularities Beyond NLO

09.04.2018 to 12.04.2018
Vittorio del Duca (ETH Zurich and INFN), Lorenzo Magnea (Turin U. and INFN), Einan Gardi (Edinburgh)

Higgs Centre for Theoretical Physics, JCMB, Edinburgh

Precise theoretical predictions for LHC observables are a crucial pre-requisite for the discovery of new physics. Such predictions require high-order perturbative calculations in the Standard Model, most notably in QCD. A key step in these calculations is the cancellation of infrared divergences, which arise from exchanges of virtual partons and from the integration over undetected real radiation. This problem is completely solved at next-to-leading order (NLO) in the QCD coupling, and several methods have been proposed and implemented to perform the cancellation at next-to-next-to-leading order (NNLO). The implementation of existing methods for generic processes at NNLO remains challenging, while extensions beyond NNLO are beginning to be studied.

The lack of striking signals of new physics in the experimental LHC results to date strongly suggests that possible Beyond-the-Standard-Model (BSM) effects will be accessible only through precision studies. Furthermore, as the LHC accumulates integrated luminosity and statistical errors are consequently reduced, the challenge for the theory community is to similarly reduce theoretical uncertainties. The subtraction of infrared singularities is a crucial ingredient to perform precise high-order calculation of collider observables. As several competing methods are being developed, the proposed workshop would be a timely and essential forum for addressing the technical issues facing the field, sharing ideas, and developing general and flexible tools to extend current ideas to more complicated process and higher orders.

The goal of the proposed workshop is to bring together the leading experts in the field, in particular the proponents of existing methods at NNLO, with the goal of 

- comparing existing methods and assessing their strengths and limitations;
- quantifying the analytical and numerical challenges for the application of the proposed methods to general multi-jet QCD processes at NNLO;
- preparing the ground for extensions of the method beyond NNLO;
- studying the implications of all-order information from amplitude-level factorisation theorems for the problem of subtraction at high-orders.