24 research outputs found

    Decoupling of heavy quarks in HQET

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    Decoupling of c-quark loops in b-quark HQET is considered. The decoupling coefficients for the HQET heavy-quark field and the heavy-light quark current are calculated with the three-loop accuracy. The last result can be used to improve the accuracy of extracting f_B from HQET lattice simulations (without c-quark loops). The decoupling coefficient for the flavour-nonsinglet QCD current with n antisymmetrized gamma-matrices is also obtained at three loops; the result for the tensor current (n=2) is new.Comment: JHEP3 documentclass; the results in a computer-readable form can be found at http://www-ttp.physik.uni-karlsruhe.de/Progdata/ttp06/ttp06-25/ V2: a few typos corrected, a few minor text improvements, a few references added; V3: several typos in formulas fixe

    Three-loop HQET vertex diagrams for B^0 -\bar{B}^0 mixing

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    Three-loop vertex diagrams in HQET needed for sum rules for B^0 - \bar{B}^0 mixing are considered. They depend on two residual energies. An algorithm of reduction of these diagrams to master integrals has been constructed. All master integrals are calculated exactly in d dimensions; their epsilon expansions are also obtained.Comment: JHEP documentclas

    Matching the heavy-quark fields in QCD and HQET at four loops

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    The QCD/HQET matching coefficient for the heavy-quark field is calculated up to four loops. It must be finite; this requirement produces analytical results for some terms in the four-loop on-shell heavy-quark field renormalization constant which were previously only known numerically. The effect of a non-zero lighter-flavor mass is calculated up to three loops. A class of on-shell integrals with two masses is analyzed in detail. By specifying our result to QED, we obtain the relation between the electron field and the Bloch--Nordsieck field with four-loop accuracy.Comment: 20 pages. v2: ref. [48] added, small changes in the text, corresponds to the journal versio

    On one master integral for three-loop on-shell HQET propagator diagrams with mass

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    An exact expression for the master integral I_2 arising in three-loop on-shell HQET propagator diagrams with mass is derived and its analytical expansion in the dimensional regularization parameter epsilon is given.Comment: 6 pages, 1 figure; v3: completely re-written, 2 new authors, many new results, additional reference

    Hybrid Renormalization of Penguins and Dimension-5 Heavy--Light Operators

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    We discuss the renormalization of local, scalar and pseudoscalar dimension-5 operators containing a heavy and a light quark field at scales below the heavy-quark mass, using the formalism of the heavy-quark effective theory (HQET). We calculate the anomalous dimensions of these operators and their mixing to one-loop order. We also perform the one-loop matching of gluon and photon penguin operators onto operators of the HQET. We discuss applications of our results to the mixing of gluon and photon penguin operators at low renormalization scales, and to the calculation of 1/mQ21/m_Q^2 corrections to meson decays constants.Comment: 18 pages, 4 figures include

    Simultaneous decoupling of bottom and charm quarks

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    We compute the decoupling relations for the strong coupling, the light quark masses, the gauge-fixing parameter, and the light fields in QCD with heavy charm and bottom quarks to three-loop accuracy taking into account the exact dependence on mc/mbm_c/m_b. The application of a low-energy theorem allows the extraction of the three-loop effective Higgs-gluon coupling valid for extensions of the Standard Model with additional heavy quarks from the decoupling constant of αs\alpha_s.Comment: 30 page

    Hybrid Renormalization of Penguins and Dimension-5 Heavy--Light Operators

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    We discuss the renormalization of local, scalar and pseudoscalar dimension5 operators containing a heavy and a light quark field at scales below the heavy-quark mass, using the formalism of the heavy-quark effective theory (HQET). We calculate the anomalous dimensions of these operators and their mixing to one-loop order. We also perform the one-loop matching of gluon and photon penguin operators onto operators of the HQET. We discuss applications of our results to the mixing of gluon and photon penguin operators at low renormalization scales, and to the calculation of 1=m 2 Q corrections to meson decays constants. (Submitted to Nuclear Physics B) CERN-TH/96-238 December 1 Introduction Local operators containing both heavy and light quark fields exhibit an interesting behaviour under renormalization at scales below the heavy-quark mass mQ . Then there arise large logarithms of the type ff s ln(mQ=ÂŻ), characterizing the exchange of gluons that are "hard" with respect to the light ..
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