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Calculating the pion decay constant from α_s(M_Z)

Michio Hashimoto·Masaharu Tanabashi
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Abstract

We revisit the analysis of the improved ladder Schwinger-Dyson (SD) equation for the dynamical chiral symmetry breaking in QCD with emphasizing the importance of the scale ambiguity. Previous calculation done so far naively used one-loop MSbar coupling in the improved ladder SD equation without examining the scale ambiguity. As a result, the calculated pion decay constant f_πwas less than a half of its experimental value f_π=92.4MeV once the QCD scale is fixed from the high energy coupling α_s(M_Z). In order to settle the ambiguity in a proper manner, we adopt here in the present paper the next-to-leading-order effective coupling instead of a naive use of the MSbar coupling. The pion decay constant f_πis then calculated from high energy QCD coupling strength α_s(M_Z)=0.1172 \pm 0.0020. Within the Higashijima-Miransky approximation, we obtain f_π=85--106MeV depending on the value of α_s(M_Z) which agrees well with the experimentally observed value f_π=92.4MeV. The validity of the improved ladder SD equation is therefore ascertained more firmly than considered before.

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Michio Hashimoto, Masaharu Tanabashi. 2002-10-08. Calculating the pion decay constant from α_s(M_Z). https://arxiv.org/abs/hep-ph/0210115

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