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preprints:2008:ttp08-01 [2016/03/17 11:03] (current)
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 +====== TTP08-01 Hadronic Z- and tau-Decays in Order alpha_s^4 ====== 
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 +   <​hidden TTP08-01 ​ Hadronic Z- and tau-Decays in Order alpha_s^4 > Using recently developed methods for the evaluation of five-loop amplitudes in perturbative QCD, corrections of order alpha_s^4 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 are evaluated. The new terms lead to a significant stabilization of the perturbative series, to a reduction of the theory uncertainly in the strong coupling constant alpha_s, as extracted from these measurements,​ and to a small shift of the central value, moving two central values closer together. The agreement between two values of alpha_s measured at vastly different energies constitutes a striking test of asymptotic freedom. Combining the results from Z and tau decays we find 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. ​  
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 +|**P.A. Baikov, K.G. Chetyrkin and  J.H.K\"​uhn** ​ |  
 +|**  Phys. Rev. Lett.  101 012002 2008  **  | 
 +| {{preprints:​2008:​ttp08-01.pdf|PDF}} {{preprints:​2008:​ttp08-01.ps|PostScript}} [[http://​arxiv.org/​abs/​0801.1821|arXiv]] ​  | 
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