Lattice determinations of the strong coupling

TL;DR

This paper provides a comprehensive pedagogical overview of lattice QCD methods for determining the strong coupling constant, emphasizing systematic errors and methodology to aid future precision improvements relevant for LHC phenomenology.

Contribution

It offers a detailed, self-contained introduction to lattice determinations of the strong coupling, focusing on methodologies and systematic errors rather than individual studies.

Findings

Lattice QCD provides the most precise determinations of the strong coupling.

Systematic errors in lattice determinations differ from those in other observables.

Understanding these errors is crucial for improving precision for LHC applications.

Abstract

Lattice QCD has reached a mature status. State of the art lattice computations include $u,d,s$ (and even the $c$) sea quark effects, together with an estimate of electromagnetic and isospin breaking corrections for hadronic observables. This precise and first principles description of the standard model at low energies allows the determination of multiple quantities that are essential inputs for phenomenology and not accessible to perturbation theory. One of the fundamental parameters that are determined from simulations of lattice QCD is the strong coupling constant, which plays a central role in the quest for precision at the LHC. Lattice calculations currently provide its best determinations, and will play a central role in future phenomenological studies. For this reason we believe that it is timely to provide a pedagogical introduction to the lattice determinations of the strong coupling. Rather than analysing individual studies, the emphasis will be on the methodologies and the systematic errors that arise in these determinations. We hope that these notes will help lattice practitioners, and QCD phenomenologists at large, by providing a self-contained introduction to the methodology and the possible sources of systematic error. The limiting factors in the determination of the strong coupling turn out to be different from the ones that limit other lattice precision observables. We hope to collect enough information here to allow the reader to appreciate the challenges that arise in order to improve further our knowledge of a quantity that is crucial for LHC phenomenology.