1,910 research outputs found
Renormalizability of the massive Yang-Mills theory
It is shown that the massive Yang-Mills theory is on mass-shell
renormalizable. Thus the Standard Model of electroweak interactions can be
modified by removing terms with the scalar field from the Lagrangian in the
unitary gauge. The resulting electroweak theory without the Higgs particle is
on mass-shell renormalizable and unitary.Comment: 9 page
Relating Physical Observables in QCD without Scale-Scheme Ambiguity
We discuss the St\"uckelberg-Peterman extended renormalization group
equations in perturbative QCD, which express the invariance of physical
observables under renormalization-scale and scheme-parameter transformations.
We introduce a universal coupling function that covers all possible choices of
scale and scheme. Any perturbative series in QCD is shown to be equivalent to a
particular point in this function. This function can be computed from a set of
first-order differential equations involving the extended beta functions. We
propose the use of these evolution equations instead of perturbative series for
numerical evaluation of physical observables. This formalism is free of
scale-scheme ambiguity and allows a reliable error analysis of higher-order
corrections. It also provides a precise definition for as the pole in the associated 't Hooft scheme. A concrete application to
is presented.Comment: Plain TEX, 4 figures (available upon request), 22 pages,
DOE/ER/40322-17
Three loop MSbar renormalization of QED in the 't~Hooft-Veltman gauge
Quantum electrodynamics (QED) fixed in the 't~Hooft-Veltman gauge is
renormalized to three loops in the MSbar scheme. The beta-functions and
anomalous dimensions are computed as functions of the usual QED coupling and
the additional coupling, xi, which is introduced as part of the nonlinear gauge
fixing condition. Similar to the maximal abelian gauge of quantum
chromodynamics, the renormalization of the gauge parameter is singular.Comment: 8 latex page
Commensurate Scale Relations in Quantum Chromodynamics
We use the BLM method to show that perturbatively-calculable observables in
QCD can be related to each other without renormalization scale or scheme
ambiguity. We define and study the commensurate scale relations. We show that
the commensurate scales satisfy the renormalization group transitivity rule
which ensures that predictions in PQCD are independent of the choice of an
intermediate renormalization scheme. We generalize the BLM procedure to higher
order. The application of this procedure to relate known physical observables
in QCD gives surprisingly simple results. In particular, the annihilation ratio
and the Bjorken sum rule for polarized electroproduction are
related through simple coefficients, which reinforces the idea of a hidden
symmetry between these two observables.Comment: 35 pages (RevTeX), one PostScript figure included at the end.
SLAC-PUB-6481, UMD Preprint #94-13
from decays: contour-improved versus fixed-order summation in a new QCD perturbation expansion
We consider the determination of from hadronic decays, by
investigating the contour-improved (CI) and the fixed-order (FO)
renormalization group summations in the frame of a new perturbation expansion
of QCD, which incorporates in a systematic way the available information about
the divergent character of the series. The new expansion functions, which
replace the powers of the coupling, are defined by the analytic continuation in
the Borel complex plane, achieved through an optimal conformal mapping. Using a
physical model recently discussed by Beneke and Jamin, we show that the new
CIPT approaches the true results with great precision when the perturbative
order is increased, while the new FOPT gives a less accurate description in the
regions where the imaginary logarithms present in the expansion of the running
coupling are large. With the new expansions, the discrepancy of 0.024 in
between the standard CI and FO summations is reduced to
only 0.009. From the new CIPT we predict , which practically coincides with the result of the
standard FOPT, but has a more solid theoretical basis
Higgs Decay to Top Quarks at O(\alpha_s^2)
Three-loop corrections to the scalar and pseudo-scalar current correlator are
calculated. By applying the large momentum expansion mass terms up to order
(m^2/q^2)^4 are evaluated analytically. As an application O(\alpha_s^2)
corrections to the decay of a scalar and pseudo-scalar Higgs boson into top
quarks are considered. It is shown that for a Higgs mass not far above the
threshold these higher order mass corrections are necessary to get
reliable results.Comment: Latex, 20 pages, 14 ps-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
Strong Coupling Constant with Flavour Thresholds at Four Loops in the MS-bar Scheme
We present in analytic form the matching conditions for the strong coupling
constant alpha_s^(n_f)(mu) at the flavour thresholds to three loops in the
modified minimal-subtraction scheme. Taking into account the recently
calculated coefficient beta_3 of the Callan-Symanzik beta function of quantum
chromodynamics, we thus derive a four-loop formula for alpha_s^(n_f)(mu)
together with appropriate relationships between the asymptotic scale parameters
Lambda^(n_f) for different numbers of flavours n_f.Comment: 10 pages (Latex), 3 figures (Postscript
Calculating loops without loop calculations: NLO computation of pentaquark correlators
We compute next-to-leading order (NLO) perturbative QCD corrections to the
correlators of interpolating pentaquark currents. We employ modular techniques
in configuration space which saves us from the onus of having to do loop
calculations. The modular technique is explained in some detail. We present
explicit NLO results for several interpolating pentaquark currents that have
been written down in the literature. Our modular approach is easily adapted to
the case of NLO corrections to multiquark correlators with an arbitrary number
of quarks/antiquarks.Comment: 23 pages, 1 figure, published version. arXiv admin note: text overlap
with arXiv:hep-lat/031001
Higher moments of nucleon spin structure functions in heavy baryon chiral perturbation theory and in a resonance model
The third moment of the twist-3 part of the nucleon spin structure
function is generalized to arbitrary momentum transfer and is
evaluated in heavy baryon chiral perturbation theory (HBChPT) up to order
and in a unitary isobar model (MAID). We show how to link
as well as higher moments of the nucleon spin structure functions
and to nucleon spin polarizabilities. We compare our results with the
most recent experimental data, and find a good description of these available
data within the unitary isobar model. We proceed to extract the twist-4 matrix
element which appears in the suppressed term in the twist
expansion of the spin structure function for proton and neutron.Comment: 30 pages, 7 figure
The dependence of the measured asymmetry : the test of the Bjorken sum rule
We analyse the proton and deutron data on spin dependent asymmetry
supposing the DIS structure functions and
have the similar -dependence. As a result, we have obtained
that at and
at , what is in the
best agreement with the Bjorken sum rule predictions.Comment: LaTeX, 5 pages, no figures, to be published in JETP Letter
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