1,948 research outputs found
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
Multi-Loop Results, Charm- and Bottom-Quark Masses and the Strong Coupling Constant
The impact of recent multi-loop calculations on precise determinations of
charm- and bottom-quark masses and the strong coupling constant is discussed.Comment: ICHEP08 proceedin
Moments of heavy-light current correlators up to three loops
We consider moments of the non-diagonal vector, axial-vector, scalar and
pseudo-scalar current correlators involving two different massive quark
flavours up to three-loop accuracy. Expansions around the limits where one mass
is zero and the equal-mass case are computed. These results are used to
construct approximations valid for arbitrary mass values.Comment: 21 page
Beta functions and anomalous dimensions up to three loops
We derive an algorithm for automatic calculation of perturbative
-functions and anomalous dimensions in any local quantum field theory
with canonical kinetic terms. The infrared rearrangement is performed by
introducing a common mass parameter in all the propagator denominators. We
provide a set of explicit formulae for all the necessary scalar integrals up to
three loops.Comment: 22 pages, 4 figures, uses epsf.st
MATAD: a program package for the computation of MAssive TADpoles
In the recent years there has been an enormous development in the evaluation
of higher order quantum corrections. An essential ingredient in the practical
calculations is provided by vacuum diagrams, i.e. integrals without external
momenta. In this paper a program package is described which can deal with one-,
two- and three-loop vacuum integrals with one non-zero mass parameter. The
principle structure is introduced and the main parts of the package are
described in detail. Explicit examples demonstrate the fields of application.Comment: 37 pages, to be published in Comp. Phys. Commu
QCD Decoupling at Four Loops
We present the matching condition for the strong coupling contant alpha_s at
a heavy quark threshold to four loops in the modified minimal subtraction
scheme. Our results lead to further decrease of the theoretical uncertainty of
the evolution of the strong coupling constant through heavy quark thresholds.
Using a low energy theorem we furthermore derive the effective coupling of the
Higgs boson to gluons (induced by a virtual heavy quark) in four- and
(partially) through five-loop approximation.Comment: 21 pages, 2 figures, the complete paper is also available via the www
at http://www-ttp.physik.uni-karlsruhe.de/Preprints
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
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