353 research outputs found
Constraints on the Leading-Twist Pion Distribution Amplitude from A QCD Light-Cone Sum Rule with Chiral Current
We present an improved analysis of the constraints on the first two
Gegenbauer moments, and , of the pion's leading-twist
distribution amplitude from a QCD light-cone sum rule analysis of
weak transition form factor . Proper chiral current is adopted in
QCD light-cone sum rule so as to eliminate the most uncertain twist-3
contributions to , and then we concentrate our attention on the
properties of the leading-twist pion DA. A nearly model-independent
as shown in Ref.\cite{pball0} that is based on the spectrum of
decays from BaBar, together with their uncertainties, are adopted as the
standard shape for to do our discussion. From a minimum -fit
and by taking the theoretical uncertainties into account, we obtain
and
at the confidence level for .Comment: 10 pages, 4 figures. References added. To be published in EPJ
Explicit results for all orders of the epsilon-expansion of certain massive and massless diagrams
An arbitrary term of the epsilon-expansion of dimensionally regulated
off-shell massless one-loop three-point Feynman diagram is expressed in terms
of log-sine integrals related to the polylogarithms. Using magic connection
between these diagrams and two-loop massive vacuum diagrams, the
epsilon-expansion of the latter is also obtained, for arbitrary values of the
masses. The problem of analytic continuation is also discussed.Comment: 8 pages, late
Form Factors from QCD Light-Cone Sum Rules
We derive new QCD sum rules for and form factors. The
underlying correlation functions are expanded near the light-cone in terms of
-meson distribution amplitudes defined in HQET, whereas the -quark mass
is kept finite. The leading-order contributions of two- and three-particle
distribution amplitudes are taken into account. From the resulting light-cone
sum rules we calculate all B\to \Dst form factors in the region of small
momentum transfer (maximal recoil). In the infinite heavy-quark mass limit the
sum rules reduce to a single expression for the Isgur-Wise function. We compare
our predictions with the form factors extracted from experimental B\to \Dst l
\nu_l decay rates fitted to dispersive parameterizations.Comment: 20 pages, 6 figures; one reference, one figure and several comments
added; version to appear in European Physical Journal
Unitarity Constraints on the B and B^* Form Factors from QCD Analyticity and Heavy Meson Spin Symmetry
A method of deriving bounds on the weak meson form factors, based on
perturbative QCD, analyticity and unitarity, is generalized in order to fully
exploit heavy quark spin symmetry in the ground state doublet of
pseudoscalar and vector mesons. All the relevant form factors of
these mesons are taken into account in the unitarity sum. They are treated as
independent functions along the timelike axis, being related by spin symmetry
only near the zero recoil point. Heavy quark vacuum polarisation up to three
loops in perturbative QCD and the experimental cross sections are used as input. We obtain bounds on the charge radius
of the elastic form factor of the meson, which considerably improve
previous results derived in the same framework.Comment: 13 pages LaTex, 1 figure as a separate ps fil
Analysis of the vector form factors and with light-cone QCD sum rules
In this article, we calculate the vector form factors and
within the framework of the light-cone QCD sum rules
approach. The numerical values of the are compatible with the
existing theoretical calculations, the central value of the ,
, is in excellent agreement with the values from the chiral
perturbation theory and lattice QCD. The values of the are
very large comparing with the theoretical calculations and experimental data,
and can not give any reliable predictions. At large momentum transfers with
, the form factors and can
either take up the asymptotic behavior of or decrease more
quickly than , more experimental data are needed to select the
ideal sum rules.Comment: 22 pages, 16 figures, revised version, to appear in Eur. Phys. J.
Implications of the Top Quark Mass Measurement for the CKM Parameters, and CP Asymmetries
Motivated by the recent determination of the top quark mass by the CDF
collaboration, \mt =174 \pm 10 ^{+13}_{-12} GeV, we review and update the
constraints on the parameters of the quark flavour mixing matrix in
the standard model. In performing our fits, we use inputs from the measurements
of the following quantities: (i) \abseps, the CP-violating parameter in
decays, (ii) \delmd, the mass difference due to the \bdbdbar\ mixing, (iii)
the matrix elements \absvcb and \absvub, and (iv) -hadron lifetimes. We
find that the allowed region of the unitarity triangle is very large, mostly
due to theoretical uncertainties. (This emphasizes the importance of
measurements of CP-violating rate asymmetries in the system.) Nevertheless,
the present data do somewhat restrict the allowed values of the coupling
constant product and the renormalization-scale
invariant bag constant . With the updated CKM matrix we present the
currently-allowed range of the ratio , as well as
the standard model predictions for the \bsbsbar\ mixing parameter \xs and the
quantities , and , which characterize
the CP-asymmetries in -decays. The ALEPH collaboration has recently reported
a significant improvement on the lower limit on the \bs-\bsb mass
difference, (95\% C.L.). This has interesting
consequences for the CKM parameters which are also worked out.
NOTE: this is a revised and updated version of our previous paper.Comment: LaTeX, 27 pages, 16 uuencoded figures (enclosed), CERN-TH.7398/94,
UdeM-GPP-TH-94-0
2019 WSES guidelines for the management of severe acute pancreatitis
Although most patients with acute pancreatitis have the mild form of the disease, about 20-30% develops a severe form, often associated with single or multiple organ dysfunction requiring intensive care. Identifying the severe form early is one of the major challenges in managing severe acute pancreatitis. Infection of the pancreatic and peripancreatic necrosis occurs in about 20-40% of patients with severe acute pancreatitis, and is associated with worsening organ dysfunctions. While most patients with sterile necrosis can be managed nonoperatively, patients with infected necrosis usually require an intervention that can be percutaneous, endoscopic, or open surgical. These guidelines present evidence-based international consensus statements on the management of severe acute pancreatitis from collaboration of a panel of experts meeting during the World Congress of Emergency Surgery in June 27-30, 2018 in Bertinoro, Italy. The main topics of these guidelines fall under the following topics: Diagnosis, Antibiotic treatment, Management in the Intensive Care Unit, Surgical and operative management, and Open abdomen. © 2019 The Author(s).Peer reviewe
Low Energy Theory for 2 flavors at High Density QCD
We construct the effective Lagrangian describing the low energy excitations
for Quantum Chromodynamics with two flavors at high density. The non-linear
realization framework is employed to properly construct the low energy
effective theory. The light degrees of freedom, as required by 't Hooft anomaly
conditions, contain massless fermions which we properly include in the
effective Lagrangian. We also provide a discussion of the linearly realized
Lagrangian.Comment: 17 pages, RevTeX format, references added. To appear in Phys. Rev.
Conservative versus interventional treatment for spontaneous pneumothorax
BACKGROUND: Whether conservative management is an acceptable alternative to interventional management for uncomplicated, moderate-to-large primary spontaneous pneumothorax is unknown. METHODS: In this open-label, multicenter, noninferiority trial, we recruited patients 14 to 50 years of age with a first-known, unilateral, moderate-to-large primary spontaneous pneumothorax. Patients were randomly assigned to immediate interventional management of the pneumothorax (intervention group) or a conservative observational approach (conservative-management group) and were followed for 12 months. The primary outcome was lung reexpansion within 8 weeks. RESULTS: A total of 316 patients underwent randomization (154 patients to the intervention group and 162 to the conservative-management group). In the conservative-management group, 25 patients (15.4%) underwent interventions to manage the pneumothorax, for reasons prespecified in the protocol, and 137 (84.6%) did not undergo interventions. In a complete-case analysis in which data were not available for 23 patients in the intervention group and 37 in the conservative-management group, reexpansion within 8 weeks occurred in 129 of 131 patients (98.5%) with interventional management and in 118 of 125 (94.4%) with conservative management (risk difference, -4.1 percentage points; 95% confidence interval [CI], -8.6 to 0.5; P = 0.02 for noninferiority); the lower boundary of the 95% confidence interval was within the prespecified noninferiority margin of -9 percentage points. In a sensitivity analysis in which all missing data after 56 days were imputed as treatment failure (with reexpansion in 129 of 138 patients [93.5%] in the intervention group and in 118 of 143 [82.5%] in the conservative-management group), the risk difference of -11.0 percentage points (95% CI, -18.4 to -3.5) was outside the prespecified noninferiority margin. Conservative management resulted in a lower risk of serious adverse events or pneumothorax recurrence than interventional management. CONCLUSIONS: Although the primary outcome was not statistically robust to conservative assumptions about missing data, the trial provides modest evidence that conservative management of primary spontaneous pneumothorax was noninferior to interventional management, with a lower risk of serious adverse events. (Funded by the Emergency Medicine Foundation and others; PSP Australian New Zealand Clinical Trials Registry number, ACTRN12611000184976.)
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