Seminário com o Dr Jean-Loic Kneur – 31 de outubro de 2014 – 10h15min
O PROGRAMA DE PÓS-GRADUAÇÃO EM FÍSICA convida para o seminário:
“Renormalization Group Optimized Perturbation: alpha_S from f_pi” *
Dr Jean-Loic Kneur – Laboratoire Charles Coulomb / Universite de Montpellier, France
*Presença obrigatória para os alunos matriculados na disciplina seminários
Resumo:
A new version of the optimized perturbation (OPT), implementing renormalization group properties consistently, allows to calculate the nonperturbative ratio $F_\pi/\Lambda_{\overline{MS}}$ of the pion decay constant and the basic QCD scale. From the experimental $F_\pi$ input value it gives a new determination of $\Lambda_{\overline{MS}}$ for $n_f=2$ and $n_f=3$, and thus of the QCD coupling $\overline\alpha_S $ at various scales once combined with a standard perturbative evolution. The empirical convergence properties of the RGOPT modified series is exhibited up to the third order. We examine the various sources of theoretical uncertainties and obtain $\alpha_S (m_Z) =0.1174 ^{+.0010}_{-.0005} \pm .001$, where the first errors are estimates of the intrinsic theoretical uncertainties of our method, and the second errors come from present uncertainties in $F_\pi/F_0$, where $F_0$ is $F_\pi$ in the exact chiral $\mbox{SU(3)}$ limit.
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