Low-energy interactions of Nambu-Goldstone bosons with DD mesons in covariant chiral perturbation theory

We calculate the scattering lengths of Nambu-Goldstone bosons interacting with $D$ mesons in a covariant formulation of chiral perturbation theory, which satisfies heavy-quark spin symmetry and analytical properties of loop amplitudes. We compare our results with previous studies performed using heavy meson chiral perturbation theory and show that recoil corrections are sizable in most cases.Comment: 3 figures and 4 table

On the role of the magnetic field on jet emission in X-ray binaries

Radio and X-ray fluxes of accreting black holes in their hard state are known to correlate over several orders of magnitude. This correlation however shows a large scatter: black hole candidates with very similar X-ray luminosity, spectral energy distribution and variability, show rather different radio luminosities. This challenges theoretical models that aim at describing both the radio and the X-ray fluxes in terms of radiative emission from a relativistic jet. More generally, it opens important questions on how similar accretion flows can produce substantially different outflows. Here we present a possible explanation for this phenomenon, based on the strong dependency of the jet spectral energy distribution on the magnetic field strength, and on the idea that the strength of the jet magnetic field varies from source to source. Because of the effect of radiative losses, sources with stronger jet magnetic field values would have lower radio emission. We discuss the implications of this scenario, the main one being that the radio flux does not necessarily provide a direct measure of the jet power. We further discuss how a variable jet magnetic field, reaching a critical value, can qualitatively explain the observed spectral transition out of the hard state.Comment: 4 pages, 2 figures. Accepted for publication on ApJ Letter

Non perturbative chiral approach to s-wave \bar{K}N interactions

The s-wave meson-nucleon interaction in the $S = -1$ sector is studied by means of coupled-channel Lippmann Schwinger equations, using the lowest order chiral Lagrangian and a cut off to regularize the loop integrals. The method reproduces succesfully the $\Lambda (1405)$ resonance and the $K^- p \to K^- p, \bar{K}^0 n, \pi^0 \Lambda, \pi^0 \Sigma, \pi^+ \Sigma^-, \pi^- \Sigma^+$ cross sections at low energies. The inclusion of the $\eta \Lambda, \eta \Sigma^0$ channels in the coupled system is found very important and allows a solution in terms of only the lowest order Lagrangian.Comment: 34 pages, 11 figures, uses epsf.sty, submitted to Nucl.Phys.

Chiral dynamics of kaon-nucleon interactions, revisited

The anti-kaon nucleon system close to threshold is analyzed in view of the new accurate DEAR kaonic hydrogen data. The calculations are performed using chiral SU(3) effective field theory in combination with non-perturbative schemes based on coupled channels. Several variants of such approaches are compared with experimental data and the differences in the results are discussed. Coulomb and isospin breaking effects turn out to be important and are both taken into account. The pole structure of the Lambda(1405) resonance close to the anti-kaon nucleon threshold is critically examined.Comment: 30 pages, 14 figures, 11 table

The Role of Lambda(1405) in Kaon-Proton Interactions

S-wave $K^-p$ scattering into various channels near threshold are analyzed in heavy-baryon chiral perturbation theory with $\Lambda (1405)$ introduced as an independent field. This is the approach that predicted the critical density $2<=\rho_c/\rho_0 <=3$ for negatively charged kaon condensation. We show that chiral perturbation expansion treating the $\Lambda (1405)$ as elementary is consistent with {\it all} threshold data including a double-charge-exchange process suppressed at leading order of chiral expansion in the absence of the $\Lambda (1405)$. We also discuss S-wave $K^+ p$ scattering phase shifts at low energy.Comment: 12 pages, epsfig.sty, 1 figure (uuencoded

New insights into antikaon-nucleon scattering and the structure of the Lambda(1405)

We perform a combined analysis of antikaon-nucleon scattering cross sections and the recent SIDDHARTA kaonic hydrogen data in the framework of a coupled-channel Bethe-Salpeter approach at next-to-leading order in the chiral expansion of the effective potential. We find a precise description of the antikaon-proton scattering amplitudes and are able to extract accurate values of the scattering lengths, a0=-1.81^+0.30_-0.28 + i 0.92^+0.29_-0.23 fm, a1=+0.48^+0.12_-0.11 + i 0.87^+0.26_-0.20 fm. We also discuss the two-pole structure of the Lambda(1405).Comment: 7 pages, 4 figure

Гидроимпульсный силовой механизм сваебойной машины в условиях обустройства месторождений

AbstractObjectivesThis study sought to evaluate whether objective assessment of the myocardial functional reserve, using strain rate imaging (SRI), allows accurate detection of viable myocardium.BackgroundStrain rate imaging is a new echocardiographic modality that allows quantitative assessment of segmental myocardial contractility.MethodsIn 37 patients (age 58 ± 9 years) with ischemic left ventricular dysfunction, myocardial viability was assessed using low-dose (10 μg/kg body weight per min) two-dimensional dobutamine stress echocardiography (DSE), tissue Doppler imaging, SRI and 18F-fluorodeoxyglucose (18FDG) positron emission tomography (PET). The peak systolic tissue Doppler velocity and peak systolic myocardial strain rate were determined at baseline and during low-dose dobutamine stress from the apical views.ResultsA total of 192 segments with dyssynergy at rest were classified by 18FDG PET as viable in 94 and nonviable in 98. An increase of peak systolic strain rate from rest to dobutamine stimulation by more than −0.23 1/s allowed accurate discrimination of viable from nonviable myocardium, as determined by 18FDG PET with a sensitivity of 83% and a specificity of 84%. Receiver operating characteristic (ROC) curve analysis showed an area under the curve for prediction of nonviable myocardium, as determined by 18FDG PET using SRI, of 0.89 (95% confidence interval [CI] 0.88 to 0.90), whereas the area under the ROC curve using tissue Doppler imaging was 0.63 (95% CI 0.61 to 0.65).ConclusionsThe increase in the peak systolic strain rate during low-dose dobutamine stimulation allows accurate discrimination between different myocardial viability states. Strain rate imaging is superior to two-dimensional DSE and tissue Doppler imaging for the assessment of myocardial viability

Chiral Dynamics of Low-Energy Kaon-Baryon Interactions with Explicit Resonance

The processes involving low energy $\bar{K}N$ and $Y\pi$ interactions (where $Y= \Sigma$ or $\Lambda$) are studied in the framework of heavy baryon chiral perturbation theory with the $\Lambda$(1405) resonance appearing as an independent field. The leading and next-to-leading terms in the chiral expansion are taken into account. We show that an approach which explicitly includes the $\Lambda$(1405) resonance as an elementary quantum field gives reasonable descriptions of both the threshold branching ratios and the energy dependence of total cross sections.Comment: 16 pages, 6 figure

Chiral Dynamics and the Low Energy Kaon-Nucleon Interaction

We examine the meson-baryon interaction in the strangeness S=-1 sector using an effective chiral Lagrangian. Potentials are derived from this Lagrangian and used in a coupled-channel calculation of the low energy observables. The potentials are constructed such that in the Born approximation the s-wave scattering amplitude is the same as that given by the effective chiral Lagrangian, up to order $q^2$. Comparison is made with the available low energy hadronic data of the coupled $K^-p, \Sigma \pi, \Lambda \pi$ system, which includes the $\Lambda (1405)$ resonance, $K^-p$ elastic and inelastic scattering, and the threshold branching ratios of the $K^-p$ decay. Good fits to the experimental data and estimates of previously unknown Lagrangian parameters are obtained.Comment: 20 pages, 10 postscript figures, uses revtex, e-mail addresses: [email protected], [email protected], [email protected]