(San Francisco State University)
Aula Seminari (LNF)
Via Enrico Fermi, 40
00044 Frascati (Roma)
We review our recent determination of the strong coupling $\alpha_s$ from the OPAL data for non-strange hadronic tau decays. We find that $\alpha_s(m^2_\tau) =0.325\pm 0.018$ using fixed-order perturbation theory, and $\alpha_s(m^2_\tau)=0.347\pm 0.025$ using contour-improved perturbation theory. These errors are larger than those claimed in previous determinations of $\alpha_s$ from tau decays. The reasons for this are several: (1) The spectral-data moments used in the standard analysis are likely to have an unreliable perturbative expansion, and OPE corrections have not been treated systematically; (2) Violations of quark-hadron duality have been ignored; (3) The nominally more precise ALEPH data are flawed because the correlation matrix is incomplete. We thus consider our determination to supersede all previous values.