3,299 research outputs found

    Five-loop fermion anomalous dimension for a general gauge group from four-loop massless propagators

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    We extend the O(αs5){\cal O}(\alpha_s^5) result of the analytic calculation of the quark mass anomalous dimension in pQCD [1] to the case of a generic gauge group. We present explicit formulas which express the relevant renormalization constants in terms of four-loop massless propagators. We also use our result to shed new light on the old puzzle of the absence of even zetas in results of perturbative calculations for a class of physical observables.Comment: An important reference [47] is correcte

    Scalar Correlator at O(alpha_s^4), Higgs Decay into b-quarks and Bounds on the Light Quark Masses

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    We compute, for the first time, the absorptive part of the massless correlator of two quark scalar currents in five loops. As physical applications we consider the O(alpha_s^4) corrections to the decay rate of the Standard Model Higgs boson into quarks, as well as the constraints on the strange quark mass following from QCD sum rules.Comment: 5 pages, REVTeX4. Few references updated. The final version, accepted for publication. The complete paper is also available via the www at http://www-ttp.physik.uni-karlsruhe.de/Preprints

    Quark Mass and Field Anomalous Dimensions to O(αs5){\cal O}(\alpha_s^5)

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    We present the results of the first complete analytic calculation of the quark mass and field anomalous dimensions to O(αs5){\cal O}(\alpha_s^5) in QCD

    Hadronic Z- and tau-Decays in Order alpha_s^4

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    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 result for the strong coupling constant in order alpha_s^4.Comment: few citations added, final published versio
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