63 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
Progress in multiloop calculations
I briefly summarize the talks on calculation of multiloop Feynman diagrams
presented at ACAT'2002 (Moscow University).Comment: Section summary talk at ACAT'2002 (Moscow
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 QCD and HQET at three loops
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
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
Three-Loop Chromomagnetic Interaction in HQET
We compute the three-loop QCD corrections to the quark chromomagnetic moment
and thus obtain the matching coefficient and the anomalous dimension of the
chromomagnetic interaction in HQET. As a byproduct we obtain the three-loop
corrections to the quark anomalous magnetic moment.Comment: 22 page
Mott scattering of polarized electrons in a strong laser field
We present analytical and numerical results of the relativistic calculation
of the transition matrix element and differential cross section for
Mott scattering of initially polarized Dirac particles (electrons) in the
presence of strong laser field with linear polarization. We use exact
Dirac-Volkov wave functions to describe the dressed electrons and the collision
process is treated in the first Born approximation. The influence of the laser
field on the degree of polarization of the scattered electron is reported.Comment: 12 pages, 11 figures, Revte
Generalization of the BLM procedure and its scales in any order of pQCD
The Brodsky--Lepage--Mackenzie procedure is sequentially and unambiguously
extended to any fixed order of perturbative QCD beyond the so called
``large--\beta_0 approximation''. As a result of this procedure, the obtained
perturbation series looks like a continued-fraction representation. A
subsequent generalization of this procedure is developed, in order to optimize
the convergence of the final series, along the lines of the Fastest Convergence
Prescription. This generalized BLM procedure is applied to the Adler D function
and also to R_{e^+e^-} in QCD at NLO. A further extension of the sequential
BLM is presented which makes use of additional parameters to optimize the
convergence of the power-series at any fixed order of expansion.Comment: 24 pages, JHEP3, 4 figures are enclosed as eps-file, final version to
be published in JHE
Asymptotics of the perturbative series for f_{B^*}/f_B
We investigate the structure of the leading IR renormalon singularity in the
QCD/HQET matching coefficients for heavy-light quark currents beyond the
large-\beta_0 limit. From this result, we derive the large-order behaviour of
the perturbative series for these coefficients, and for ratios of meson matrix
elements, such as f_{B^*}/f_B.Comment: 45 pages, 2 eps figures. v2: small corrections, reference added. v3:
reference added. v4: errors in some equations of Appendix B, in (5.8) and
Table 2 corrected, numerical changes are very small. Paper also available
from http://www-ttp.physik.uni-karlsruhe.de/Preprints
Matching QCD and HQET heavy-light currents at three loops
We consider the currents formed by a heavy and a light quark within Quantum
Chromodynamics and compute the matching to Heavy Quark Effective Theory to
three-loop accuracy. As an application we obtain the third-order perturbative
corrections to ratios of B-meson decay constants.Comment: 23 pages, full results are available as Mathematica files at
http://www-ttp.particle.uni-karlsruhe.de/Progdata/ttp09/ttp09-41/ ; v2: an
error in comparison with Ref. [8] fixed ; v3: Journal versio
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