4,457 research outputs found

    Anomalous dimension of gluonic operator in polarized deep inelastic scattering at O(1/N_f)

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    We compute the O(1/N_f) correction to the predominantly gluonic flavour singlet twist-2 anomalous dimension used in polarized deep inelastic scattering. It is consistent with known two loop perturbation theory and we determine the three loop contribution at O(1/N_f). The treatment of the epsilon-tensor in the large N_f d-dimensional critical point formalism is also discussed.Comment: 8 Latex pages, 1 postscript figur

    Structure function evolution at next-to-leading order and beyond

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    Results are presented of two studies addressing the scaling violations of deep-inelastic structure functions. Factorization-scheme independent fits to all ep and mu p data on F_2 are performed at next-to-leading order (NLO), yielding alpha_s(M_Z) = 0.114 +- 0.002_exp (+0.006-0.004)_th . In order to reduce the theoretical error dominated by the renormalization-scale dependence, the next-higher order (NNLO) needs to be included. For the flavour non-singlet sector, it is shown that available calculations provide sufficient information for this purpose at x > 10^-2.Comment: 3 pages LaTeX including 4 eps-figures, uses npb.sty. Talk presented at DIS'99, DESY-Zeuthen, April 1999. To appear in the proceeding

    The 4-loop quark mass anomalous dimension and the invariant quark mass

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    We present the analytical calculation of the four-loop quark mass anomalous dimension in Quantum Chromodynamics within the minimal subtraction scheme. On the basis of this result we find that the so-called invariant quark mass is a very good reference mass for the accurate evolution of the running MS-bar quark mass in phenomenological applications. We also obtain for the first time a complete 4-th order perturbative QCD expression for a physical quantity, the total Higgs boson decay rate into hadrons, and analyze the infrared fixed point for this case.Comment: 11 pages, Late

    On the role of the quark mass thresholds in extrapolations of the running \alpha_s

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    The accuracy of the conventional treatment of quark mass thresholds in the QCD running coupling constant αs\alpha_s, based on the step approximation to the β\beta--function, is investigated. The errors of extrapolating \ase(\mu) from low energies to μ=MZ\mu=M_Z, implied by this approximation, are shown to be of the same magnitude as the typical next--to--next--to--leading order contributions to \as and tend to increase the resulting \as. The importance of the proper choice of matching points is emphasized.Comment: latex, 7 pages, 2 uuencoded figure

    The 16th Moment of the Non--Singlet Structure Functions F2(x,Q2)F_2(x,Q^2) and FL(x,Q2)F_L(x,Q^2) to O(αs3)O(\alpha_s^3)

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    We present the results of an analytic next--to--next--to leading order QCD calculation of the non--singlet anomalous dimension γNS+(N)\gamma_{\rm NS}^+(N) and the coefficient functions C2,L(N)C_{2,L}(N) associated to the deeply inelastic structure functions F2(x,Q2)F_2(x,Q^2) and FL(x,Q2)F_L(x,Q^2) for the Mellin moment N=16. Comparisons are made with results in the literature.Comment: 11 pages, 1 style file, 1 figur

    Matching QCD and HQET at three loops

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    QCD/HQET matching for the heavy-quark field and heavy-light quark currents with three-loop accuracy is discussed.Comment: Talk at Loops and Legs 2010, Woerlitz, 25-30 April, 7 pages; v2: references adde