Hyperon Nonleptonic Decays in Chiral Perturbation Theory Reexamined

We recalculate the leading nonanalytic contributions to the amplitudes for hyperon nonleptonic decays in chiral perturbation theory. Our results partially disagree with those calculated before, and include new terms previously omitted in the P-wave amplitudes. Although these modifications are numerically significant, they do not change the well-known fact that good agreement with experiment cannot be simultaneously achieved using one-loop S- and P-wave amplitudes.Comment: 14 pages, latex, 3 figures, uses axodraw.sty, minor additions, to appear in Phys. Rev.

Socioeconomic deprivation and age are barriers to the online collection of patient reported outcome measures in orthopaedic patients

Introduction: Questionnaires are used commonly to assess functional outcome and satisfaction in surgical patients. Although these have in the past been administered through written forms, there is increasing interest in the use of new technology to improve the efficiency of collection. The aim of this study was to assess the availability of internet access for a group of orthopaedic patients and the acceptability of online survey completion. Methods: A total of 497 patients attending orthopaedic outpatient clinics were surveyed to assess access to the internet and their preferred means for completing follow-up questionnaires. Results: Overall, 358 patients (72%) reported having internet access. Lack of access was associated with socioeconomic deprivation and older age. Multivariable regression confirmed increased age and greater deprivation to be independently associated with lack of internet access. Out of the total group, 198 (40%) indicated a preference for assessment of outcomes via email and the internet. Conclusions: Internet access was not universal among the patients in our orthopaedic clinic. Reliance on internet collection of PROMs may introduce bias by not including results from patients in older age groups and those from the more deprived socioeconomic groups

Hyperons in Two Flavor Chiral Perturbation Theory

We use two-flavor chiral perturbation theory to describe hyperons. We focus on the strangeness conserving sector, and, as an example, calculate hyperon masses. Convergence of this two-flavor chiral expansion for observables is improved over the three-flavor theory. The cost, however, is a larger number of low-energy constants that must be ultimately determined from lattice QCD data. A formula for the mass of the omega baryon is derived to sixth order in this expansion, and will aid lattice practitioners in scale setting or tuning the strange quark mass.Comment: 14 pages, 3 figs, version published in PL

Chronic hypoxia down-regulates tight junction protein ZO-2 expression in children with cyanotic congenital heart defect

AIMS: Tight junction protein zonula occludens protein 2 (ZO-2) is a member of the membrane-associated guanylate kinases protein family known to be expressed at tight junctions of epithelial and endothelial cells and at adherens junctions (AJs) in cardiomyocytes. Little is known about ZO-2 expression and function in the human heart. Here, we examined the hypothesis that chronic hypoxia down-regulates ZO-2 expression in human myocardium and cultured rat cardiomyocytes. METHODS AND RESULTS: Patients with a diagnosis of cyanotic (n = 10) or acyanotic (n = 10) Tetralogy of Fallot undergoing surgical repair were used to examine ZO-2 messenger RNA and protein expression by real time-PCR, immunohistochemistry, and western blotting. A model of cultured rat cardiomyocytes was used to measure ZO-2 and AJ proteins levels in response to hypoxia and to investigate ZO-2 cellular localization. We showed that ZO-2 is expressed in myocardial tissue in acyanotic and cyanotic children with congenital heart defects. ZO-2 was specifically down-regulated in cyanotic myocardium at both the messenger RNA and protein levels when compared with acyanotic patients. This specific down-regulation can be mimicked in cultured rat cardiomyocytes by treating them with hypoxic conditions confirming that ZO-2 gene down-regulation is specifically due to cyanosis. Furthermore, in addition to its cytoplasmic expression, ZO-2 showed nuclear expression in cultured rat cardiomyocytes suggesting potential role in transcription regulation. CONCLUSIONS: Hypoxia down-regulates ZO-2 expression in both cyanotic patient's myocardium and cultured rat cardiomyocytes. This down-regulation suggest an involvement of ZO-2 in cardiac remodelling of AJs in cyanotic children and may explain the greater susceptibility of cyanotic patients to corrective heart surgery

Chiral Perturbation Theory for |Delta I|=3/2 Hyperon Decays

We study the |Delta I|=3/2 amplitudes of hyperon non-leptonic decays of the form B->B'+pi in the context of chiral perturbation theory. The lowest-order predictions are determined in terms of only one unknown parameter and are consistent within errors with current data. We investigate the theoretical uncertainty of these predictions by calculating the leading non-analytic corrections. We also present an estimate for the size of the S-wave Lambda and Cascade decays which vanish at leading order. We find that the corrections to the lowest-order predictions are within the expectations of naive power counting and, therefore, that this picture can be tested more accurately with improved measurements.Comment: 22 pages, latex, 4 figures, uses axodraw.sty, few typos correcte

Delta Baryon Magnetic Moments From Lattice QCD

Theoretical predictions for the magnetic moments of the physical Delta baryons are extracted from lattice QCD calculations. We utilize finite-range regulated effective field theory that is constructed to have the correct Dirac moment mass dependence in the region where the up and down quark masses are heavy. Of particular interest is the chiral nonanalytic behaviour encountered as the nucleon-pion decay channel opens. We find a Delta^++ magnetic moment (at the Delta pole) of 4.99 \pm 0.56 \mu_N. This result is within the Particle Data Group range of 3.7-7.5 \mu_N and compares well with the experimental result of Bosshard et al. of 4.52 \pm 0.51 \pm 0.45 \mu_N. The interplay between the different pion-loop contributions to the Delta^+ magnetic moment leads to the surprising result that the proton moment may exceed that of the Delta^+, contrary to conventional expectations.Comment: 7 pages, 7 figures, RevTex 4; Updated to include a recent experimental resul

Quenched Chiral Perturbation Theory for Vector Mesons

We develop quenched chiral perturbation theory for vector mesons made of light quarks, in the limit where the vector meson masses are much larger than the pion mass. We use this theory to extract the leading nonanalytic dependence of the vector meson masses on the masses of the light quarks. By comparing with analogous quantities computed in ordinary chiral perturbation theory, we estimate the size of quenching effects, observing that in general they can be quite large. This estimate is relevant to lattice simulations, where the $\rho$ mass is often used to set the lattice spacing.Comment: 18 pages, 8 figures, uses REVTeX and epsf.st

CP Violation in Hyperon Nonleptonic Decays within the Standard Model

We calculate the CP-violating asymmetries A(Lambda_-^0) and A(Xi_-^-) in nonleptonic hyperon decay within the Standard Model using the framework of heavy-baryon chiral perturbation theory (chiPT). We identify those terms that correspond to previous calculations and discover several errors in the existing literature. We present a new result for the lowest-order (in chiPT) contribution of the penguin operator to these asymmetries, as well as an estimate for the uncertainty of our result that is based on the calculation of the leading nonanalytic corrections.Comment: 21 pages, 2 figures; discussion clarified, results & conclusions unchanged, to appear in Phys. Rev.

Electromagnetic and weak hyperon properties in the Skyrme model

We report on the result of some investigations concerning the radiative decays of decuplet baryons and the non-leptonic weak decays of the octet baryons in the context of topological chiral soliton models. Our results are compared with those of alternative baryon models. For the radiative decays we find that the predictions are similar to those of quark models. In the case of the non-leptonic weak decays, we find that although the predicted S-wave amplitudes are in rather good agreement with the observed values, the model is not able to reproduce the empirical P-wave amplitudes. Thus, in contrast to previous expectations, the Skyrme model does not seem to provide a solution to the long-standing 'S-wave/P-wave puzzle'.Comment: 7 pages, 1 fig. Cont. to the Proc. of the "School on Electromagnetic probes and the structure of hadrons and nuclei". Erice, Italy. September 17- 24, 1999 to be published in Progress in Particle and Nuclear Physic

Weak decays of the B_c meson to B_s and B mesons in the relativistic quark model

Semileptonic and nonleptonic decays of the B_c meson to B_s and B mesons, caused by the c\to s,d quark transitions, are studied in the framework of the relativistic quark model. The heavy quark expansion in inverse powers of the active c and spectator \bar b quark is used to simplify calculations while the final s and d quarks in the B_s and B mesons are treated relativistically. The decay form factors are explicitly expressed through the overlap integrals of the meson wave functions in the whole accessible kinematical range. The obtained results are compared with the predictions of other approaches.Comment: 24 pages, 12 figures, version to appear in Eur. Phys. J.