63 research outputs found
Preliminary definitions for the sonographic features of synovitis in children
Objectives Musculoskeletal ultrasonography (US) has the potential to be an important tool in the assessment of disease activity in childhood arthritides. To assess pathology, clear definitions for synovitis need to be developed first. The aim of this study was to develop and validate these definitions through an international consensus process. Methods The decision on which US techniques to use, the components to be included in the definitions as well as the final wording were developed by 31 ultrasound experts in a consensus process. A Likert scale of 1-5 with 1 indicating complete disagreement and 5 complete agreement was used. A minimum of 80% of the experts scoring 4 or 5 was required for final approval. The definitions were then validated on 120 standardized US images of the wrist, MCP and tibiotalar joints displaying various degrees of synovitis at various ages. Results B-Mode and Doppler should be used for assessing synovitis in children. A US definition of the various components (i.e. synovial hypertrophy, effusion and Doppler signal within the synovium) was developed. The definition was validated on still images with a median of 89% (range 80-100) of participants scoring it as 4 or 5 on a Likert scale. Conclusions US definitions of synovitis and its elementary components covering the entire pediatric age range were successfully developed through a Delphi process and validated in a web-based still images exercise. These results provide the basis for the standardized US assessment of synovitis in clinical practice and research
On Low-Energy Effective Actions in N = 2, 4 Superconformal Theories in Four Dimensions
We study some aspects of low-energy effective actions in 4-d superconformal
gauge theories on the Coulomb branch. We describe superconformal invariants
constructed in terms of N=2 abelian vector multiplet which play the role of
building blocks for the N=2,4 supersymmetric low-energy effective actions. We
compute the one-loop effective actions in constant N=2 field strength
background in N=4 SYM theory and in N=2 SU(2) SYM theory with four
hypermultiplets in fundamental representation. Using the classification of
superconformal invariants we then find the manifestly N=2 superconformal form
of these effective actions. While our explicit computations are done in the
one-loop approximation, our conclusions about the structure of the effective
actions in N=2 superconformal theories are general. We comment on some
applications to supergravity - gauge theory duality in the description of
D-brane interactions.Comment: 18 pages, latex, comments/reference adde
The vertex with arbitrary gluon virtualities in the perturbative QCD hard scattering approach
We study the vertex for arbitrary gluon virtualities in
the time-like and space-like regions, using the perturbative QCD hard
scattering approach and an input wave-function of the -meson
consistent with the measured transition form
factor. The contribution of the gluonic content of the -meson is
taken into account, enhancing the form factor over the entire virtuality
considered. However, data on the electromagnetic transition form factor of the
-meson is not sufficient to quantify the gluonic enhancement. We
also study the effect of the transverse momenta of the partons in the
-meson on the vertex, using the modified
hard scattering approach based on Sudakov formalism. Analytic expressions for
the vertex are presented in limiting kinematic regions
and parametrizations are given satisfying the QCD anomaly, for real gluons, and
perturbative QCD behavior for large gluon virtualities, in both the time-like
and space-like regions. Our results have implications for the inclusive decay
and exclusive decays, such as , and in hadronic production processes .Comment: 23 pages, 19 figures (requires revtex4, amssymb, epsf); several typos
corrected, this version now identical to the one accepted for publication in
Phys. Rev.
Exclusive Radiative B-Decays in the Light-Cone QCD Sum Rule Approach
We carry out a detailed study of exclusive radiative rare -decays in the
framework of the QCD sum rules on the light cone, which combines the
traditional QCD sum rule technique with the description of final state vector
mesons in terms of the light-cone wave functions of increasing twist. The
decays considered are: and the corresponding decays of the mesons, and . Based on our estimate of the transition
form factor F_1^{B \to K^*\pg}(0) =0.32\pm0.05, we find for the branching
ratio , which is in
agreement with the observed value measured by the CLEO collaboration. We
present detailed estimates for the ratios of the radiative decay form factors,
which are then used to predict the rates for the exclusive radiative B-decays
listed above. This in principle allows the extraction of the CKM matrix element
from the penguin-dominated CKM-suppressed radiative decays when they
are measured. We give a detailed discussion of the dependence of the form
factors on the -quark mass and on the momentum transfer, as well as their
interrelation with the CKM-suppressed semileptonic decay form factors in , which we also calculate in our approach.Comment: 32 pages, 10 uuencoded figures, LaTeX, preprint CERN-TH 7118/9
Effective action of three-dimensional extended supersymmetric matter on gauge superfield background
We study the low-energy effective actions for gauge superfields induced by
quantum N=2 and N=4 supersymmetric matter fields in three-dimensional Minkowski
space. Analyzing the superconformal invariants in the N=2 superspace we propose
a general form of the N=2 gauge invariant and superconformal effective action.
The leading terms in this action are fixed by the symmetry up to the
coefficients while the higher order terms with respect to the Maxwell field
strength are found up to one arbitrary function of quasi-primary N=2
superfields constructed from the superfield strength and its covariant spinor
derivatives. Then we find this function and the coefficients by direct quantum
computations in the N=2 superspace. The effective action of N=4 gauge multiplet
is obtained by generalizing the N=2 effective action.Comment: 1+27 pages; v2: minor corrections, references adde
Superconformal operators in N=4 super-Yang-Mills theory
We construct, in the framework of the N=4 SYM theory, a supermultiplet of
twist-two conformal operators and study their renormalization properties. The
components of the supermultiplet have the same anomalous dimension and enter as
building blocks into multi-particle quasipartonic operators. The latter are
determined by the condition that their twist equals the number of elementary
constituent fields from which they are built. A unique feature of the N=4 SYM
is that all quasipartonic operators with different SU(4) quantum numbers fall
into a single supermultiplet. Among them there is a subsector of the operators
of maximal helicity, which has been known to be integrable in the multi-color
limit in QCD, independent of the presence of supersymmetry. In the N=4 SYM
theory, this symmetry is extended to the whole supermultiplet of quasipartonic
operators and the one-loop dilatation operator coincides with a Hamiltonian of
integrable SL(2|4) Heisenberg spin chain.Comment: 45 pages, Latex, 4 figure
Angular distributions in hard exclusive production of pion pairs
Using the leading order amplitudes of hard exclusive electroproduction of
pion pairs we have analyzed the angular distribution of the two produced
particles. At leading twist a pion pair can be produced only in an isovector or
an isoscalar state. We show that certain components of the angular distribution
only get contributions from the interference of the I=1 and the (much smaller)
I=0 amplitude. Therefore our predictions prove to be a good probe of isospin
zero pion pair production. We predict effects of a measurable size that could
be observed at experiments like HERMES. We also discuss how hard exclusive pion
pair production can provide us with new information on the effective chiral
Lagrangian.Comment: 17 pages, version to appear in Phys. Rev.
Parton interactions in the Bjorken limit of QCD
We consider the Bjorken limit in the framework of the effective action
approach and discuss its similarities to the Regge limit. The proposed
effective action allows for a rather simple calculation of the known evolution
kernels. We represent the result in terms of two-parton interaction operators
involving gluon and quark operators depending on light-ray position and
helicity and analyze their symmetry properties.Comment: 32 pages LaTex, 4 eps-figures, comments added, minor correction
Next-to-next-to-leading order prediction for the photon-to-pion transition form factor
We evaluate the next-to-next-to-leading order corrections to the
hard-scattering amplitude of the photon-to-pion transition form factor. Our
approach is based on the predictive power of the conformal operator product
expansion, which is valid for a vanishing -function in the so-called
conformal scheme. The Wilson--coefficients appearing in the non-forward
kinematics are then entirely determined from those of the polarized
deep-inelastic scattering known to next-to-next-to-leading accuracy. We propose
different schemes to include explicitly also the conformal symmetry breaking
term proportional to the -function, and discuss numerical predictions
calculated in different kinematical regions. It is demonstrated that the
photon-to-pion transition form factor can provide a fundamental testing ground
for our QCD understanding of exclusive reactions.Comment: 62 pages LaTeX, 2 figures, 9 tables; typos corrected, some references
added, to appear in Phys. Rev.
Integrability in QCD and beyond
Yang--Mills theories in four space-time dimensions possess a hidden symmetry
which does not exhibit itself as a symmetry of classical Lagrangians but is
only revealed on the quantum level. It turns out that the effective Yang--Mills
dynamics in several important limits is described by completely integrable
systems that prove to be related to the celebrated Heisenberg spin chain and
its generalizations. In this review we explain the general phenomenon of
complete integrability and its realization in several different situations. As
a prime example, we consider in some detail the scale dependence of composite
(Wilson) operators in QCD and super-Yang--Mills (SYM) theories. High-energy
(Regge) behavior of scattering amplitudes in QCD is also discussed and provides
one with another realization of the same phenomenon that differs, however, from
the first example in essential details. As the third example, we address the
low-energy effective action in a N=2 SYM theory which, contrary to the previous
two cases, corresponds to a classical integrable model. Finally, we include a
short overview of recent attempts to use gauge/string duality in order to
relate integrability of Yang--Mills dynamics with the hidden symmetry of a
string theory on a curved background.Comment: 87 pages, 4 figures; minor stylistic changes, references added. To be
published in the memorial volume 'From Fields to Strings: Circumnavigating
Theoretical Phyiscs', World Scientific, 2004. Dedicated to the memory of Ian
Koga
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