A Fluid Generalization of Membranes

In a certain sense a perfect fluid is a generalization of a point particle. This leads to the question as to what is the corresponding generalization for extended objects. The lagrangian formulation of a perfect fluid is much generalized and this has as a particular example a fluid which is a classical generalization of a membrane, however there is as yet no indication of any relationship between their quantum theories.Comment: To appear in CEJP, updated to coincide with published versio

Sleep problems are associated with chronic pain over and above mutual associations with depression and catastrophizing

INTRODUCTION Pain, mood problems and sleeping difficulties are often comorbid and contribute to reduced physical function and quality of life for those suffering from chronic pain. However, the way in which these factors interact is unclear. Until recently it was thought that the effect of sleep on pain and physical function was simply a result of its common association with mood problems. However, a growing body of research suggests that sleep may have a unique contribution. OBJECTIVES The aim of this study was to determine whether sleep disturbances were associated with pain and poor physical function independent of psychological distress in patients attending a tertiary pain medicine unit. METHOD 101 patients with chronic pain completed a set of questionnaires measuring pain, sleep and mood, and also completed a selection of physical assessments conducted by a physiotherapist. RESULTS 75.2% of participants had insomnia and 84.3% reported the presence of at least one sleep problem. Significant positive correlations with pain were detected for depression, catastrophizing, insomnia, short sleep duration and poor sleep quality. Sleep duration had a significant independent association with pain after accounting for depression and catastrophizing. Sleep duration also had an independent association with physical function after accounting for pain and catastrophizing. CONCLUSIONS Given that sleep has an important and unique contribution to pain and physical function, it is important that sleep disturbances are addressed both in the assessment and treatment of chronic pain

K -> pi pi and a light scalar meson

We explore the Delta-I= 1/2 rule and epsilon'/epsilon in K -> pi pi transitions using a Dyson-Schwinger equation model. Exploiting the feature that QCD penguin operators direct K^0_S transitions through 0^{++} intermediate states, we find an explanation of the enhancement of I=0 K -> pi pi transitions in the contribution of a light sigma-meson. This mechanism also affects epsilon'/epsilon.Comment: 7 pages, REVTE

Health Utilities Associated with Hemoglobin Levels and Blood Loss in Postmenopausal Women: The Women's Health Initiative

AbstractObjectivesThe purpose of our study was to use health-related quality of life data from the Women's Health Initiative to calculate health-related utility weights and examine differences in these health utility weights across different hemoglobin (Hgb) levels. These utility weights could then be used in future cost-effectiveness studies.MethodsHealth utility weights were measured by the Short Form-6D (SF-6D), a health utility index derived from the Short Form Medical Outcomes questionnaire. Adjusted least square means were calculated for each level of Hgb at baseline and in longitudinal regression analysis the relationship between change in Hgb and change in the SF-6D was examined. Both baseline and longitudinal analyses were performed for all postmenopausal women and separately for those with self-reported heart failure, cancer, and osteoarthritis.ResultsWomen with Hgb in the anemic range had lower health utility weights than those with higher Hgb levels. Longitudinally, a loss of of 2 g/dl Hgb or more was associated with a statistically significant and clinically meaningfully decline in SF-6D in all participants and also in the group of participants with cancer and osteoarthritis, but not in those with heart failure.ConclusionsLower levels of Hgb and a loss of Hgb are associated with a statistically significant and clinically meaningful decrement in health utility in all postmenopausal women we studied and also in those with chronic conditions

Non-perturbative gluons in diffractive photo-production of J/Psi

The modifications induced in the calculation of the cross section of the diffractive process gamma gamma -> J/Psi J/Psi when the gluon propagator is changed are analyzed. Instead of the usual perturbative gluon propagator, alternative forms obtained using non-perturbative methods like Dyson-Schwinger equations are used to consider in a more consistent way the contributions of the infrared region. The result shows a reduction in the differential cross-section for low momentum transfer once compared with the perturbative result, to be confirmed with future experimental results from TESLA.Comment: 17 pages, 5 figures, RevTex, Accepted for publication in Phys. Lett.

Survey of nucleon electromagnetic form factors

A dressed-quark core contribution to nucleon electromagnetic form factors is calculated. It is defined by the solution of a Poincare' covariant Faddeev equation in which dressed-quarks provide the elementary degree of freedom and correlations between them are expressed via diquarks. The nucleon-photon vertex involves a single parameter; i.e., a diquark charge radius. It is argued to be commensurate with the pion's charge radius. A comprehensive analysis and explanation of the form factors is built upon this foundation. A particular feature of the study is a separation of form factor contributions into those from different diagram types and correlation sectors, and subsequently a flavour separation for each of these. Amongst the extensive body of results that one could highlight are: r_1^{n,u}>r_1^{n,d}, owing to the presence of axial-vector quark-quark correlations; and for both the neutron and proton the ratio of Sachs electric and magnetic form factors possesses a zero.Comment: 43 pages, 17 figures, 12 tables, 5 appendice

Masses of ground and excited-state hadrons

We present the first Dyson-Schwinger equation calculation of the light hadron spectrum that simultaneously correlates the masses of meson and baryon ground- and excited-states within a single framework. At the core of our analysis is a symmetry-preserving treatment of a vector-vector contact interaction. In comparison with relevant quantities the root-mean-square-relative-error/degree-of freedom is 13%. Notable amongst our results is agreement between the computed baryon masses and the bare masses employed in modern dynamical coupled-channels models of pion-nucleon reactions. Our analysis provides insight into numerous aspects of baryon structure; e.g., relationships between the nucleon and Delta masses and those of the dressed-quark and diquark correlations they contain.Comment: 25 pages, 7 figures, 4 table

Mesons as qbar-q Bound States from Euclidean 2-Point Correlators in the Bethe-Salpeter Approach

We investigate the 2-point correlation function for the vector current. The gluons provide dressings for both the quark self energy as well as the vector vertex function, which are described consistently by the rainbow Dyson-Schwinger equation and the inhomogeneous ladder Bethe-Salpeter equation. The form of the gluon propagator at low momenta is modeled by a 2-parameter ansatz fitting the weak pion decay constant. The quarks are confined in the sense that the quark propagator does not have a pole at timelike momenta. We determine the ground state mass in the vector channel from the Euclidean time Fourier transform of the correlator, which has an exponential falloff at large times. The ground state mass lies around 590 MeV and is almost independent of the model form for the gluon propagator. This method allows us to stay in Euclidean space and to avoid analytic continuation of the quark or gluon propagators into the timelike region.Comment: 21 pages (REVTEX), 8 Postscript figure

Critical scaling of the a.c. conductivity for a superconductor above Tc

We consider the effects of critical superconducting fluctuations on the scaling of the linear a.c. conductivity, \sigma(\omega), of a bulk superconductor slightly above Tc in zero applied magnetic field. The dynamic renormalization- group method is applied to the relaxational time-dependent Ginzburg-Landau model of superconductivity, with \sigma(\omega) calculated via the Kubo formula to O(\epsilon^{2}) in the \epsilon = 4 - d expansion. The critical dynamics are governed by the relaxational XY-model renormalization-group fixed point. The scaling hypothesis \sigma(\omega) \sim \xi^{2-d+z} S(\omega \xi^{z}) proposed by Fisher, Fisher and Huse is explicitly verified, with the dynamic exponent z \approx 2.015, the value expected for the d=3 relaxational XY-model. The universal scaling function S(y) is computed and shown to deviate only slightly from its Gaussian form, calculated earlier. The present theory is compared with experimental measurements of the a.c. conductivity of YBCO near Tc, and the implications of this theory for such experiments is discussed.Comment: 16 pages, submitted to Phys. Rev.