255 research outputs found
Mass Corrections to the Vector Current Correlator
Three-loop QCD corrections to the vector current correlator are considered.
The large momentum procedure is applied in order to evaluate mass corrections
up to order . The inclusion of the first seven terms to the ratio
leads to reliable
predictions from the high energy region down to relatively close to threshold.Comment: 16 pages, LaTeX, 11 postscript figures. The complete paper, including
figures, is also available via anonymous ftp at
ftp://ttpux2.physik.uni-karlsruhe.de/ , or via www at
http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints
Four-Loop Decoupling Relations for the Strong Coupling
We compute the matching relation for the strong coupling constant within the
framework of QCD up to four-loop order. This allows a consistent five-loop
running (once the function is available to this order) taking into
account threshold effects. As a side product we obtain the effective coupling
of a Higgs boson to gluons with five-loop accuracy.Comment: 11 page
Threshold expansion for heavy-light systems and flavor off-diagonal current-current correlators
An expansion scheme is developed for Feynman diagrams describing the
production of one massive and one massless particle near the threshold. As an
example application, we compute the correlators of heavy-light quark currents,
(\bar b gamma_mu u) and (\bar b gamma_5 u), through O(alpha_s^2).Comment: 4 pages, revtex
R(s) and hadronic tau-Decays in Order alpha_s^4: technical aspects
We report on some technical aspects of our calculation of alpha_s^4
corrections to R(s) and the semi-leptonic tau decay width [1-3]. We discuss the
inner structure of the result as well as the issue of its correctness. We
demonstrate recently appeared independent evidence positively testing one of
two components of the full result
Quartic Mass Corrections to
The influence of nonvanishing quark masses on the total cross section in
electron positron collisions and on the decay rate is calculated. The
corrections are expanded in and \as. Methods similar to those applied
for the quadratic mass terms allow to derive the corrections of order \as
m^4/s^2 and \as^2m^4/s^2. Coefficients which depend logarithmically on
and which cannot be absorbed in a running quark mass arise in order
\as^2. The implications of these results on electron positron annihilation
cross sections at LEP and at lower energies in particular between the charm and
the bottom threshold and for energies several GeV above the threshold
are discussed.Comment: 17 pages, LaTex (uses epsf.sty, figures appended as uuencoded ps- and
eps-files). A complete postscript file, including figures, is available via
anonymous ftp at ttpux2.physik.uni-karlsruhe.de (129.13.102.139) as
/pub/ttp94-08/ttp94-08.ps, Local preprint# TTP94-0
Higher Moments of Heavy Quark Vacuum Polarization
We present analytical calculation of the first seven moments of the heavy
quark vacuum polarization function in the three-loop order. The obtained
results are compared against the asymptotic formulas following from the
threshold singularities. We also discuss the dependence of the moments
within the BLM procedure.Comment: 9 pages, LaTeX, no figures, sprocl.sty provided (To appear in the
Proceedings of the Second Workshop on Continuous Advances in QCD,
Minneapolis, U.S.A., March 1996). Postscript also available at
ftp://www-ttp.physik.uni-karlsruhe.de/ttp96-22/ttp96-22.ps or at
http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints
Hoelder Inequalities and QCD Sum-Rule Bounds on the Masses of Light Quarks
QCD Laplace Sum-Rules must satisfy a fundamental Hoelder inequality if they
are to consistently represent an integrated hadronic spectral function. The
Laplace sum-rules of pion currents is shown to violate this inequality unless
the and quark masses are sufficiently large, placing a lower bound on
, the SU(2)-invariant combination of the light-quark masses.Comment: 3 pages, latex, write-up of talk presented at DPF 200
Recent progress in computing four-loop massive correlators
We report about recent progress in computing four-loop massive correlators.
The expansion of these correlators in the external momentum leads to vacuum
integrals. The calculation of these vacuum integrals can be used to determine
Taylor expansion coefficients of the vacuum polarization function and
decoupling functions in perturbative Quantum chromodynamics. New results at
four-loop order for the lowest Taylor expansion coefficient of the vacuum
polarization function and for the decoupling relation are presented.Comment: 4 pages, talk given at the 12th International Conference on Quantum
Chromodynamics, Montpellier, 4-8th July 200
Four-loop renormalization of QCD: full set of renormalization constants and anomalous dimensions
The anomalous dimensions of the gluon and ghost fields as well as the
ghost-ghost-gluon and quark-quark-gluon vertexes are analytically computed in
pQCD. Taken together with already available anomalous dimensions of the
coupling constant, the quark field and the mass the results lead to complete
knowledge of all renormalization constant entering into the renormalization of
the QCD Lagrangian at the four-loop level. As a by-product we get scale and
scheme invariant gluon and ghost propagators at NNNLO. Using a theorem due to
Dudal, Verschelde and Sorella, we also construct the four-loop anomalous
dimension of the ``gluon mass operator'', A^2, in the Landau gauge.Comment: a reference added. Final version accepted for publication in Nucl.
Phys. B. Full list of the results can be found (in a computer-readable form)
in http://www-ttp.physik.uni-karlsruhe.de/Progdata/ttp04/ttp04-08
Double Bubble Corrections to Heavy Quark Production
Second order corrections to the heavy quark production
cross-section due to massless quarks and coloured scalars are calculated for
all energies above threshold. Based on the method introduced in this letter
also the gauge non-invariant second order corrections due to the pure gluonic
selfenergy insertion and a certain class of and
corrections are determined. For the special choice of
the gauge parameter, , the leading threshold and high energy behaviour
of the pure second order gluonic corrections to the cross-section are governed
by the gluonic self energy insertion.Comment: 9 pages, latex, 17 figures, the complete postscript file of this
preprint, including figures, is available via anonymous ftp at
ftp://www-ttp.physik.uni-karlsruhe.de/ttp96-04/ttp96-04.ps (129.13.102.139)
or via www at http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints
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