Scale Setting Using the Extended Renormalization Group and the Principle of Maximum Conformality: the QCD Coupling Constant at Four Loops
By S. Brodsky, Xing-Gang Wu. 2011
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A key problem in making precise perturbative QCD predictions is to set the proper renormalization scale of the running coupling. The extended renormalization group equations, which express the invariance of physical observables under both the renormalization scale- and scheme-parameter transformations, provide a convenient way for estimating the scale- and scheme-dependence of the physical process. In this paper, we present a solution for the scale-equation of the extended renormalization group equations at the four-loop level. Using the principle of maximum conformality (PMC)/Brodsky-Lepage-Mackenzie (BLM) scale-setting method, all non-conformal {beta}{sub i} terms in the perturbative expansion series can be summed into the running coupling, and the resulting scale-fixed predictions are independent of the renormalization scheme. Different schemes lead to different effective PMC/BLM scales, but the final results are scheme independent. Conversely, from the requirement of scheme independence, one not only can obtain scheme-independent commensurate scale relations among different observables, but also determine the scale displacements among the PMC/BLM scales which are derived under different schemes. In principle, the PMC/BLM scales can be fixed order-by-order, and as a useful reference, we present a systematic and scheme-independent procedure for setting PMC/BLM scales up to NNLO. An explicit application for determining the scale setting of R{sub e{sup +}e{sup -}}(Q) up to four loops is presented. By using the world average {alpha}{sub s}{sup {ovr MS}}(MZ) = 0.1184 {+-} 0.0007, we obtain the asymptotic scale for the 't Hooft associated with the {ovr MS} scheme, {Lambda}{sub {ovr MS}}{sup 'tH} = 245{sub -10}{sup +9} MeV, and the asymptotic scale for the conventional {ovr MS} scheme, {Lambda}{sub {ovr MS}} = 213{sub -8}{sup +19} MeV.
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Citations in the corpus
- Systematic Scale-Setting to All Orders: The Principle of Maximum Conformality and Commensurate Scale Relations (2013, methodology): “where ci = βiβ i−1 0 /β i 1 are the rescaled β-function coefficients and C is an arbitrary integration constant which in Rδ is set to C = lnβ(2) 0/β1 in order to reproduce the standard ΛMS scale [2, 9, 33] .”
- The QCD running coupling (2016, methodology): “in which the physical basis is the non-relativistic heavy quark phenomenology [59] or the eects of gluon radiation [60]. 3.7.3 Principle of maximum conformality The Principle of Maximum Conformality [61,62,52] provides a rigorous generalization of the BLM procedure. In this method, one rst generaliz”