644 research outputs found
Low-energy interactions of Nambu-Goldstone bosons with mesons in covariant chiral perturbation theory
We calculate the scattering lengths of Nambu-Goldstone bosons interacting
with 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 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 resonance and the cross
sections at low energies. The inclusion of the
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 scattering into various channels near threshold are analyzed in
heavy-baryon chiral perturbation theory with introduced as an
independent field. This is the approach that predicted the critical density
for negatively charged kaon condensation. We show that
chiral perturbation expansion treating the 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
. We also discuss S-wave 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 and interactions (where
or ) are studied in the framework of heavy baryon chiral
perturbation theory with the (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 (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 . Comparison is made with the available low energy
hadronic data of the coupled system, which
includes the resonance, elastic and inelastic
scattering, and the threshold branching ratios of the 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]
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