Gauhar Abbas, B. Ananthanarayan, Irinel Caprini
We revisit the extraction of $\alpha_s(M_\tau^2)$ from the QCD perturbative
corrections to the hadronic $\tau$ branching ratio, using an improved
fixed-order perturbation theory based on the explicit summation of all
renormalization-group accessible logarithms, proposed some time ago in the
literature. In this approach, the powers of the coupling in the expansion of
the QCD Adler function are multiplied by a set of functions $D_n$, which depend
themselves on the coupling and can be written in a closed form by iteratively
solving a sequence of differential equations. We find that the new expansion
has an improved behaviour in the complex energy plane compared to that of the
standard fixed-order perturbation theory (FOPT), and is similar but not
identical to the contour-improved perturbation theory (CIPT). With five terms
in the perturbative expansion we obtain in the ${\bar{\rm MS}}$ scheme $
\alpha_s(M_\tau^2)= 0.338 \pm 0.010$.
View original:
http://arxiv.org/abs/1202.2672
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