Abstract
The effective renormalizable theory describing electromagnetic and strong interactions of quarks of five light flavors (nf=5QCD×QED) is considered as a low-energy limit of the full Standard Model. Two-loop relation between the running strong coupling constants αs 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 αs with a high-energy one with increased accuracy. Numerical impact of new O(αsα) terms is studied at the MZ scale. It is shown that the corresponding contribution, although being suppressed with respect to O(αs2) terms, is an order of magnitude larger than the three-loop QCD corrections O(αs3) usually taken into account in four-loop renormalization group evolution of αs. The dependence on the matching scale is also analyzed numerically.
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