Progress in NNLO calculations for scattering processes

TL;DR

The paper argues that NNLO calculations are essential to reduce theoretical uncertainties in perturbative QCD across multiple scattering processes. It surveys the motivations for NNLO, detailing reductions in scale uncertainties, improved jet algorithm matching, and better shape predictions, while highlighting the need for NNLO parton distributions. It then reviews major advances in two-loop master integrals and amplitudes, including methods like IBP/LI reductions and Mellin-Barnes techniques, and discusses the status of infrared factorization at two loops. Finally, it outlines the remaining tasks to build NNLO parton-level Monte Carlo generators, emphasizing subtraction schemes and the combination of all NNLO contributions, with optimism for progress by the next workshop.

Abstract

The various motivations for improving the perturbative prediction to next-to-next-to-leading order (NNLO) for basic scattering processes in proton-(anti)proton, electron-proton and electron-positron scattering are discussed in detail. Recent progress in the field of next-to-next-to-leading order calculations is reviewed.

Figures (2)

• Figure 1: Single jet inclusive distribution at $E_T = 100$ GeV and $0.1 < |\eta| < 0.7$ at $\sqrt{s} = 1800$ GeV at LO (green), NLO (blue) and NNLO (red). The solid and dashed red lines how the NNLO prediction if $A_4=0$, $A_4= \pm A_3^2/A_2$ respectively. The same pdf's and $\alpha_s$ are used throughout.
• Figure 2: The average value of $\langle 1-T\rangle$ given by Eq. \ref{['eq:omt']} showing the NLO prediction (dashed red), the NLO prediction with power correction of $\lambda = 1$ GeV (solid blue) and an NNLO estimate with $A_3=3$ and a power correction of $\lambda=0.5$ GeV (green dots).