849 research outputs found
The generalized parton distributions of the nucleon in the NJL model based on the Faddeev approach
We study the generalized parton distributions, including the helicity-flip
ones, using Nambu-Jona-Lasinio model based on a relativistic Faddeev approach
with `static approximation'. Sum rules relating the generalized parton
distributions to nucleon electromagnetic form factors are satisfied. Moreover,
quark-antiquark contributions in the region are non-vanishing. Our
results are qualitatively similar to those calculated with Radyushkin's double
distribution ansatz using forward parton distribution functions calculated in
the NJL model as inputs.Comment: 35 pages, 15 figure
A Faddeev Calculation for Pentaquark in Diquark Picture with Nambu-Jona-Lasinio Type Interaction
A Bethe-Salpeter-Faddeev (BSF) calculation is performed for the pentaquark
in the diquark picture of Jaffe and Wilczek in which is a
diquark-diquark- three-body system.
Nambu-Jona-Lasinio (NJL) model is used to calculate the lowest order diagrams
in the two-body scatterings of and . With the use of coupling
constants determined from the meson sector, we find that
interaction is attractive while interaction is repulsive, and there is no
bound pentaquark state. A bound pentaquark can only be
obtained with unphysically strong vector mesonic coupling constants.Comment: 4 pages, 4 figure
Faddeev calculation of pentaquark in the Nambu-Jona-Lasinio model-based diquark picture
A Bethe-Salpeter-Faddeev (BSF) calculation is performed for the pentaquark
in the diquark picture of Jaffe and Wilczek in which is a
diquark-diquark- three-body system. Nambu-Jona-Lasinio (NJL) model is
used to calculate the lowest order diagrams in the two-body scatterings of
and . With the use of coupling constants determined from the
meson sector, we find that interaction is attractive in s-wave
while interaction is repulsive in p-wave. With only the lowest three-body
channel considered, we do not find a bound pentaquark state.
Instead, a bound pentaquark with is obtained with a
unphysically strong vector mesonic coupling constants.Comment: 22 pages, 11 figures, accepted version in Phys. Rev. C. Summary of
main changes/corrections: 1. "which only holds at tree level" below the eq.
(23) is added. 2. In the last paragraph of p.23 we added a remark that the
coupling constant obtained from Lambda mass is different from the estimate as
obtained from the meson spectru
A BeppoSAX observation of the super-soft source CAL87
We report on a BeppoSAX Concentrator Spectrometer observation of the
super-soft source (SSS) CAL87. The X-ray emission in SSS is believed to arise
from nuclear burning of accreted material on the surface of a white dwarf (WD).
An absorbed blackbody spectral model gives a chi^2_v of 1.18 and a temperature
of 42 +/- ^13 _11 eV. However, the derived luminosity and radius are greater
than the Eddington limit and radius of a WD. Including an O viii edge at 0.871
keV gives a significantly better fit (at > 95% confidence) and results in more
realistic values of the source luminosity and radius. We also fit WD atmosphere
models to the CAL87 spectrum. These also give reasonable bolometric
luminosities and radii in the ranges 2.7-4.8 10^{36} erg/s and 8-20 10^7 cm,
respectively. These results support the view that the X-ray emission from CAL87
results from nuclear burning in the atmosphere of a WD.Comment: 4 pages. Accepted for publication in A&A (Letters
Baryon structure in a quark-confining non-local NJL model
We study the nucleon and diquarks in a non-local Nambu-Jona-Lasinio model.
For certain parameters the model exhibits quark confinement, in the form of a
propagator without real poles. After truncation of the two-body channels to the
scalar and axial-vector diquarks, a relativistic Faddeev equation for nucleon
bound states is solved in the covariant diquark-quark picture. The dependence
of the nucleon mass on diquark masses is studied in detail. We find parameters
that lead to a simultaneous reasonable description of pions and nucleons. Both
the diquarks contribute attractively to the nucleon mass. Axial-vector diquark
correlations are seen to be important, especially in the confining phase of the
model. We study the possible implications of quark confinement for the
description of the diquarks and the nucleon. In particular, we find that it
leads to a more compact nucleon.Comment: 21 pages (RevTeX), 18 figures (eps
Liquid-gas phase transition in nuclear matter including strangeness
We apply the chiral SU(3) quark mean field model to study the properties of
strange hadronic matter at finite temperature. The liquid-gas phase transition
is studied as a function of the strangeness fraction. The pressure of the
system cannot remain constant during the phase transition, since there are two
independent conserved charges (baryon and strangeness number). In a range of
temperatures around 15 MeV (precise values depending on the model used) the
equation of state exhibits multiple bifurcates. The difference in the
strangeness fraction between the liquid and gas phases is small when they
coexist. The critical temperature of strange matter turns out to be a
non-trivial function of the strangeness fraction.Comment: 15 pages, 7 figure
Luminosity Function of High-Mass X-ray Binaries and Anisotropy in the Distribution of Active Galactic Nuclei toward the Large Magellanic Cloud
In 2003-2012, the INTEGRAL observatory has performed long-term observations
of the Large Magellanic Cloud (LMC). At present, this is one of the deepest
hard X-ray (20-60 keV) surveys of extragalactic fields in which more than 20
sources of different natures have been detected. We present the results of a
statistical analysis of the population of high-mass X-ray binaries in the LMC
and active galactic nuclei (AGNs) observed in its direction. The hard X-ray
luminosity function of high-mass X-ray binaries is shown to be described by a
power law with a slope alpha~1.8, that in agreement with the luminosity
function measurements both in the LMC itself, but made in the soft X-ray energy
band, and in other galaxies. At the same time, the number of detected AGNs
toward the LMC turns out to be considerably smaller than the number of AGNs
registered in other directions, in particular, toward the source 3C 273. The
latter confirms the previously made assumption that the distribution of matter
in the local Universe is nonuniform.Comment: 5 pages, 5 figures, will be published in Astronomy Letters, 2012,
Vol. 38, No. 8, p. 492--49
Detection of Toxoplasma gondii soluble antigen, SAG-1 (p30), antibody and immune complex in the cerebrospinal fluid of HIV positive or negative individuals
Active infection by T. gondii was evaluated by immunoassay for soluble SAG-1 (p30), the major surface antigen from T. gondii, specific antibodies and immune complexes in human cerebrospinal fluid (CSF) samples. A total of 263 samples of CSF were collected from hospitalized patients presenting neurological disorders and analyzed for antibodies to HIV. Patients were divided into two groups: HIV positive (n = 96) or HIV negative (n = 167). The results of the assays showed that 45% of all samples were positive for soluble SAG-1. Toxoplasma Ag/Ab immune complexes were detected in 19% of the CSF samples and 62% were positive for T. gondii- specific IgG. A combination of these assays in the presence of clinical findings consistent with active Toxoplasma infection may predict the presence of toxoplasmic encephalitis. Moreover, detection of soluble SAG-1 in the CSF of these individuals appears consistent with active infection
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