227 research outputs found

    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

    The renormalization of the axial anomaly in dimensional regularization

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    The prescription for the Îł5\gamma_5-matrix within dimensional regularization in multiloop calculations is elaborated. The three-loop anomalous dimension of the singlet axial current is calculated.Comment: 11 pages, 1 figure available on request from the author, NIKHEF-H/92-1

    The Large Quark Mass Expansion of Gamma (Z^0 -> hadrons) and Gamma(tau^- -> nu_tau + hadrons) in the Order alpha_s^3

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    We present the analytical αs3\alpha_{s}^3 correction to the Z0Z^{0} decay rate into hadrons. We calculate this correction up to (and including) terms of the order (mZ2/mtop2)3(m_Z^2/m_{top}^2)^3 in the large top quark mass expansion. We rely on the technique of the large mass expansion of individual Feynman diagrams and treat its application in detail. We convert the obtained results of six flavour QCD to the results in the effective theory with five active flavours, checking the decoupling relation of the QCD coupling constant. We also derive the large charm quark mass expansion of the semihadronic τ\tau lepton decay rate in the αs3\alpha_{s}^3 approximation.Comment: Postscript generation repaired, The complete postscript file of this article, including figures, is now available at ftp://nikhefh.nikhef.nl/pub/preprints/H94-30.ps.g

    Dimensional Reduction applied to QCD at three loops

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    Dimensional Reduction is applied to \qcd{} in order to compute various renormalization constants in the \drbar{} scheme at higher orders in perturbation theory. In particular, the β\beta function and the anomalous dimension of the quark masses are derived to three-loop order. Special emphasis is put on the proper treatment of the so-called ϵ\epsilon-scalars and the additional couplings which have to be considered.Comment: 13 pages, minor changes, references adde

    The four-loop DRED gauge beta-function and fermion mass anomalous dimension for general gauge groups

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    We present four-loop results for the gauge beta-function and the fermion mass anomalous dimension for a gauge theory with a general gauge group and a multiplet of fermions transforming according to an arbitrary representation, calculated using the dimensional reduction scheme. In the special case of a supersymmetric theory we confirm previous calculations of both the gauge beta-function and the gaugino mass beta-function.Comment: 44 pages, added references (v2) minor changes (v3

    Production of a pseudo-scalar Higgs boson at hadron colliders at next-to-next-to leading order

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    The production cross section for pseudo-scalar Higgs bosons at hadron colliders is computed at next-to-next-to-leading order (NNLO) in QCD. The pseudo-scalar Higgs is assumed to couple only to top quarks. The NNLO effects are evaluated using an effective lagrangian where the top quarks are integrated out. The NNLO corrections are similar in size to those found for scalar Higgs boson production.Comment: 20 pages, 6 figures, JHEP style, Minor changes, Journal reference adde
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