21,205 research outputs found
A Comparative Study of the Decays in Standard Model and Supersymmetric Theories
Using improved theoretical calculations of the decay form factors in the
Light Cone-QCD sum rule approach, we investigate the decay rates, dilepton
invariant mass spectra and the forward-backward (FB) asymmetry in the decays () in the standard
model (SM) and a number of popular variants of the supersymmetric (SUSY)
models. Theoretical precision on the differential decay rates and FB-asymmetry
is estimated in these theories taking into account various parametric
uncertainties. We show that existing data on and the
experimental upper limit on the branching ratio provide interesting bounds on the coefficients of the underlying
effective theory. We argue that the FB-asymmetry in
constitutes a precision test of the SM and its measurement in forthcoming
experiments may reveal new physics. In particular, the presently allowed
large- solutions in SUGRA models, as well as more general
flavor-violating SUSY models, yield FB-asymmetries which are characteristically
different from the corresponding ones in the SM.Comment: 36 pages, 12 figures (require epsfig.sty), 8 Tables, LaTeX2e;
subsection 6.4 corrected, minor changes in numerical results, Figures 3 and 9
to 12 modified; submitted to Physical Review
Diffusion-limited aggregation as branched growth
I present a first-principles theory of diffusion-limited aggregation in two
dimensions. A renormalized mean-field approximation gives the form of the
unstable manifold for branch competition, following the method of Halsey and
Leibig [Phys. Rev. A {\bf 46}, 7793 (1992)]. This leads to a result for the
cluster dimensionality, D \approx 1.66, which is close to numerically obtained
values. In addition, the multifractal exponent \tau(3) = D in this theory, in
agreement with a proposed `electrostatic' scaling law.Comment: 13 pages, one figure not included (available by request, by ordinary
mail), Plain Te
Heavy-to-light transition form factors and their relations in light-cone QCD sum rules
The improved light-cone QCD sum rules by using chiral current correlator is
systematically reviewed and applied to the calculation of all the
heavy-to-light form factors, including all the semileptonic and penguin ones.
By choosing suitable chiral currents, the light-cone sum rules for all the form
factors are greatly simplified and depend mainly on one leading twist
distribution amplitude of the light meson. As a result, relations between these
form factors arise naturally. At the considered accuracy these relations
reproduce the results obtained in the literature. Moreover, since the explicit
dependence on the leading twist distribution amplitudes is preserved, these
relations may be more useful to simulate the experimental data and extract the
information on the distribution amplitude.Comment: 1+16 pages, no figure
The Form Factor in The Whole Kinematically Accessible Range
A systematic analysis is presented of the form factor in the whole range of momentum transfer , which would be useful to
analyzing the future data on decays and extracting .
With a modified QCD light cone sum rule (LCSR) approach, in which the
contributions cancel out from the twist 3 wavefunctions of meson, we
investigate in detail the behavior of at small and intermediate
and the nonperturbative quantity
is the decay constant of meson and
the strong coupling), whose numerical
result is used to study dependence of at large in
the single pole approximation. Based on these findings, a form factor model
from the best fit is formulated, which applies to the calculation on
in the whole kinematically accessible range. Also, a comparison is made with
the standard LCSR predictions.Comment: 11 pages, Latex, 1 eps figure, Final version to appear in Phys.Rev.
Eta-nucleon coupling constant in QCD with SU(3) symmetry breaking
We study the NN coupling constant using the method of QCD sum rules
starting from the vacuum-to-eta correlation function of the interpolating
fields of two nucleons. The matrix element of this correlation has been taken
with respect to nucleon spinors to avoid unwanted pole contribution. The
SU(3)-flavor symmetry breaking effects have been accounted for via the
-mass, s-quark mass and eta decay constant to leading order. Out of the
four sum rules obtained by taking the ratios of the two sum rules in
conjunction with the two sum rules in nucleon mass, three are found to give
mutually consistent results. We find the SU(3) breaking effects significant, as
large as 50% of the SU(3) symmetric part.Comment: 13 pages, 12 figure
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Architecture of the Short External Rotator Muscles of the Hip.
BackgroundMuscle architecture, or the arrangement of sarcomeres and fibers within muscles, defines functional capacity. There are limited data that provide an understanding of hip short external rotator muscle architecture. The purpose of this study was thus to characterize the architecture of these small hip muscles.MethodsEight muscles from 10 independent human cadaver hips were used in this study (n = 80 muscles). Architectural measurements were made on pectineus, piriformis, gemelli, obturators, quadratus femoris, and gluteus minimus. Muscle mass, fiber length, sarcomere length, and pennation angle were used to calculate the normalized muscle fiber length, which defines excursion, and physiological cross-sectional area (PCSA), which defines force-producing capacity.ResultsGluteus minimus had the largest PCSA (8.29 cm2) followed by obturator externus (4.54 cm2), whereas superior gemellus had the smallest PCSA (0.68 cm2). Fiber lengths clustered into long (pectineus - 10.38 cm and gluteus minimus - 10.30 cm), moderate (obturator internus - 8.77 cm and externus - 8.04 cm), or short (inferior gemellus - 5.64 and superior gemellus - 4.85). There were no significant differences among muscles in pennation angle which were all nearly zero. When the gemelli and obturators were considered as a single functional unit, their collective PCSA (10.00 cm2) exceeded that of gluteus minimus as a substantial force-producing group.ConclusionsThe key findings are that these muscles have relatively small individual PCSAs, short fiber lengths, and low pennation angles. The large collective PCSA and short fiber lengths of the gemelli and obturators suggest that they primarily play a stabilizing role rather than a joint rotating role
Experimental quantum verification in the presence of temporally correlated noise
Growth in the complexity and capabilities of quantum information hardware
mandates access to practical techniques for performance verification that
function under realistic laboratory conditions. Here we experimentally
characterise the impact of common temporally correlated noise processes on both
randomised benchmarking (RB) and gate-set tomography (GST). We study these
using an analytic toolkit based on a formalism mapping noise to errors for
arbitrary sequences of unitary operations. This analysis highlights the role of
sequence structure in enhancing or suppressing the sensitivity of quantum
verification protocols to either slowly or rapidly varying noise, which we
treat in the limiting cases of quasi-DC miscalibration and white noise power
spectra. We perform experiments with a single trapped Yb ion as a
qubit and inject engineered noise () to probe protocol
performance. Experiments on RB validate predictions that the distribution of
measured fidelities over sequences is described by a gamma distribution varying
between approximately Gaussian for rapidly varying noise, and a broad, highly
skewed distribution for the slowly varying case. Similarly we find a strong
gate set dependence of GST in the presence of correlated errors, leading to
significant deviations between estimated and calculated diamond distances in
the presence of correlated errors. Numerical simulations demonstrate
that expansion of the gate set to include negative rotations can suppress these
discrepancies and increase reported diamond distances by orders of magnitude
for the same error processes. Similar effects do not occur for correlated
or errors or rapidly varying noise processes,
highlighting the critical interplay of selected gate set and the gauge
optimisation process on the meaning of the reported diamond norm in correlated
noise environments.Comment: Expanded and updated analysis of GST, including detailed examination
of the role of gauge optimization in GST. Full GST data sets and
supplementary information available on request from the authors. Related
results available from
http://www.physics.usyd.edu.au/~mbiercuk/Publications.htm
Effectiveness of group-based self-management education for individuals with Type 2 diabetes:A systematic review with meta-analyses and meta-regression
Aims:
Patient education for the management of Type 2 diabetes can be delivered in various forms, with the goal of promoting and supporting positive self-management behaviours. This systematic review aimed to determine the effectiveness of group-based interventions compared with individual interventions or usual care for improving clinical, lifestyle and psychosocial outcomes in people with Type 2 diabetes.
Methods:
Six electronic databases were searched. Group-based education programmes for adults with Type 2 diabetes that measured glycated haemoglobin (HbA1c) and followed participants for ≥ 6 months were included. The primary outcome was HbA1c, and secondary outcomes included fasting blood glucose, weight, body mass index, waist circumference, blood pressure, blood lipid profiles, diabetes knowledge and self-efficacy.
Results:
Fifty-three publications describing 47 studies were included (n = 8533 participants). Greater reductions in HbA1c occurred in group-based education compared with controls at 6–10 months [n = 30 studies; mean difference (MD) = 3 mmol/mol (0.3%); 95% confidence interval (CI): −0.48, −0.15; P = 0.0002], 12–14 months [n = 27 studies; MD = 4 mmol/mol (0.3%); 95% CI: −0.49, −0.17; P < 0.0001], 18 months [n = 3 studies; MD = 8 mmol/mol (0.7%); 95% CI: −1.26, −0.18; P = 0.009] and 36–48 months [n = 5 studies; MD = 10 mmol/mol (0.9%); 95% CI: −1.52, −0.34; P = 0.002], but not at 24 months. Outcomes also favoured group-based education for fasting blood glucose, body weight, waist circumference, triglyceride levels and diabetes knowledge, but not at all time points. Interventions facilitated by a single discipline, multidisciplinary teams or health professionals with peer supporters resulted in improved outcomes in HbA1c when compared with peer-led interventions.
Conclusions:
Group-based education interventions are more effective than usual care, waiting list control and individual education at improving clinical, lifestyle and psychosocial outcomes in people with Type 2 diabetes.No Full Tex
Fitting Parton Distribution Data with Multiplicative Normalization Uncertainties
We consider the generic problem of performing a global fit to many
independent data sets each with a different overall multiplicative
normalization uncertainty. We show that the methods in common use to treat
multiplicative uncertainties lead to systematic biases. We develop a method
which is unbiased, based on a self--consistent iterative procedure. We
demonstrate the use of this method by applying it to the determination of
parton distribution functions with the NNPDF methodology, which uses a Monte
Carlo method for uncertainty estimation.Comment: 33 pages, 5 figures: published versio
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