24 research outputs found
Decoupling of heavy quarks in HQET
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
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
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
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
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 corrections to
meson decays constants.Comment: 18 pages, 4 figures include
Simultaneous decoupling of bottom and charm quarks
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 . 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 .Comment: 30 page
Hybrid Renormalization of Penguins and Dimension-5 Heavy--Light Operators
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=¯), characterizing the exchange of gluons that are "hard" with respect to the light ..