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 — preprints:2008:ttp08-28 [2016/03/15 20:38] (current) Line 1: Line 1: + ====== TTP08-28 The Strong Coupling Constant at Low and High Energies ====== + + + Recent results for the + cross section of electron-positron annihilation into hadrons and for the + decay rates of the $Z$ boson and the  $\tau$ lepton into hadrons including + ​corrections of order  $\alpha_s^4$ are reviewed. + The consistency between two values ​ of $\alpha_s$ measured + at vastly different energies constitutes + a striking test of asymptotic freedom and requires the proper matching + ​conditions + at charm and bottom thresholds. + ​Combining the results from $Z$ and $\tau$ decays + leads to $\alpha_s(M_Z)=0.1198 \pm 0.0015$ as one of the most precise and + ​presently only + NNNLO result for the strong coupling constant. We report a recent + ​determination of $\alpha_s$ + which is based on a lattice evaluation of the pseudoscalar correlator for + the charm quarks combined + with continuum perturbation theory. + ​ + |**J.H. K&​uuml;​hn** ​ | + |**      Contribution to "​Continuous Advances in QCD, 2008" Minnepolis, USA, May 15 - 18, 2008; to be published in the proceedings **  | + | {{preprints:​2008:​ttp08-28.pdf|PDF}} {{preprints:​2008:​ttp08-28.ps|PostScript}} ​  | + | |