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

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.

Comments: 9 pages, 1 figure, a small typo in Eq. 18 is corrected (thanks to S. Martin), results are not affected and can be found as ancillary files