The automation of next-to-leading order electroweak calculations

R Frederix,V Hirschi,H.-S Shao,M Zaro,D Pagani,S Frixione

doi:10.1007/jhep07(2018)185

Abstract

We present the key features relevant to the automated computation of all the leading- and next-to-leading order contributions to short-distance cross sections in a mixed-coupling expansion, with special emphasis on the first subleading NLO term in the QCD+EW scenario, commonly referred to as NLO EW corrections. We discuss, in particular, the FKS subtraction in the context of a mixed-coupling expansion; the extension of the FKS subtraction to processes that include final-state tagged particles, defined by means of fragmentation functions; and some properties of the complex mass scheme. We combine the present paper with the release of a new version of MadGraph5_aMC@NLO, capable of dealing with mixed-coupling expansions. We use the code to obtain illustrative inclusive and differential results for the 13-TeV LHC.

Highlights

With more than two-thirds of the LHC Run II completed, and a collected integrated luminosity in excess of 85 fb−1 at 13 TeV, it appears that physics beyond the Standard Model is not eager to be discovered
By following as closely as possible the procedure of the original paper [46], we have proven the cancellation of the IR singularities that emerge in the intermediate steps of the computations, and obtained in the process the IR-finite short-distance cross sections
The ones which are best motivated from the physical viewpoint all stem from the Dyson summation of the geometric series that results from the insertion of two-point 1PI graphs; this leads to the propagator

Summary

Introduction

With more than two-thirds of the LHC Run II completed, and a collected integrated luminosity in excess of 85 fb−1 at 13 TeV, it appears that physics beyond the Standard Model is not eager to be discovered. While we have no way at present to tell which of these two scenarios is the one realised by Nature, we know that they entail different long-term strategies In the former instance, we must be able to explore larger scales, by increasing collider c.m. energies; in the latter instance, we must collect more statistics and fight against systematics. Which specific perturbative orders depends obviously on the theory one considers Owing to both the large numerical values assumed by αS and the paramount importance of hadroncollision physics in the LHC era, QCD has played a prominent role in recent years — fully-differential NLO results are standard, including the cases of processes with very involved final states, while more and more NNLO and even N3LO predictions are becoming available, for low-multiplicity reactions and with different degrees of inclusiveness The ones which are best motivated from the physical viewpoint all stem from the Dyson summation of the geometric series that results from the insertion of two-point 1PI graphs; this leads to the propagator:

Objectives

Results

Conclusion