Past, present, and future of precision determinations of the QCD coupling from lattice QCD

TL;DR

This paper reviews the challenges in non-perturbative lattice QCD determinations of the QCD coupling and discusses a novel strategy leveraging heavy quark decoupling and pure Yang-Mills theory to improve precision.

Contribution

It introduces a new approach using heavy quark decoupling to relate QCD and Yang-Mills theory, enabling more precise non-perturbative coupling calculations.

Findings

Successful application of the strategy to determine the $mbda$-parameter for 3-flavor QCD.

Potential to significantly enhance the precision of lattice QCD coupling measurements.

The method is adaptable to other non-perturbative renormalization problems.

Abstract

Non-perturbative scale-dependent renormalization problems are ubiquitous in lattice QCD as they enter many relevant phenomenological applications. They require solving non-perturbatively the renormalization group equations for the QCD parameters and matrix elements of interest in order to relate their non-perturbative determinations at low energy to their high-energy counterparts needed for phenomenology. Bridging the large energy separation between the hadronic and perturbative regimes of QCD, however, is a notoriously difficult task. In this contribution we focus on the case of the QCD coupling. We critically address the common challenges that state-of-the-art lattice determinations have to face in order to be significantly improved. In addition, we review a novel strategy that has been recently put forward in order to solve this non-perturbative renormalization problem and discuss its implications for future precision determinations. The new ideas exploit the decoupling of heavy quarks to match $N_{\rm f}$-flavor QCD and the pure Yang-Mills theory. Through this matching the computation of the non-perturbative running of the coupling in QCD can be shifted to the computationally much easier to solve pure-gauge theory. We shall present results for the determination of the $\Lambda$-parameter of $N_{\rm f}=3$-flavor QCD where this strategy has been applied and proven successful. The results demonstrate that these techniques have the potential to unlock unprecedented precision determinations of the QCD coupling from the lattice. The ideas are moreover quite general and can be considered to solve other non-perturbative renormalization problems.