On the electroweak contribution to the matching of the strong coupling constant in the SM

TL;DR

This paper derives a two-loop relation for the strong coupling constant in the Standard Model, including electroweak effects, improving precision in comparing low- and high-energy determinations of lpha_s.

Contribution

It provides the first two-loop matching relation for lpha_s considering electroweak and Higgs decoupling, enhancing accuracy in lpha_s evolution.

Findings

Electroweak contributions are larger than three-loop QCD corrections at the Z boson scale.

The new lpha_s relation reduces uncertainties in high-precision tests of the Standard Model.

Dependence on the matching scale is quantitatively analyzed.

Abstract

The effective renormalizable theory describing electromagnetic and strong interactions of quarks of five light flavors ($n_f = 5$ QCD$\times$QED) is considered as a low-energy limit of the full Standard Model. Two-loop relation between the running strong coupling constants $\alpha_s$ defined in either theories is found by simultaneous decoupling of electroweak gauge and Higgs bosons in addition to the top quark. The relation potentially allows one to confront "low-energy determination of $\alpha_s$ with a high-energy one with increased accuracy. Numerical impact of new $\mathcal{O}(\alpha_s\alpha)$ terms is studied at the $M_Z$ scale. It is shown that the corresponding contribution, although being suppressed with respect to $\mathcal{O}(\alpha_s^2)$ terms, is an order of magnitude larger than the three-loop QCD corrections $\mathcal{O}(\alpha_s^3)$ usually taken into account in four-loop renormalization group evolution of $\alpha_s$. The dependence on the matching scale is also analyzed numerically.