280 research outputs found
Constraints on nuclear matter properties from QCD susceptibilities
We establish the interrelation between the QCD scalar response of the nuclear
medium and its response to a scalar probe coupled to nucleons, such as the
scalar meson responsible for the nuclear binding. The relation that we derive
applies at the nucleonic as well as at the nuclear levels. Non trivial
consequences follow. In particular it opens the possibility of relating medium
effects in the scalar meson exchange or three-body forces of nuclear physics to
QCD lattice studies of the nucleon massComment: Submitted to EPJ
Virtual Compton Scattering from the Proton and the Properties of Nucleon Excited States
We calculate the contributions to the generalized polarizabilities of
the proton in virtual Compton scattering. The following nucleon excitations are
included: , , , , ,
and . The relationship between nucleon
structure parameters, properties and the generalized polarizabilities of
the proton is illustrated.Comment: 13 pages of text (Latex) plus 4 figures (as uuencoded Z-compressed
.tar file created by csh script uufiles
Finite Nuclei in the Quark-Meson Coupling (QMC) Model
We report the first use of the effective QMC energy density functional (EDF),
derived from a quark model of hadron structure, to study a broad range of
ground state properties of even-even nuclei across the periodic table in the
non-relativistic Hartree-Fock+BCS framework. The novelty of the QMC model is
that the nuclear medium effects are treated through modification of the
internal structure of the nucleon. The density dependence is microscopically
derived and the spin-orbit term arises naturally. The QMC EDF depends on a
single set of four adjustable parameters having clear physical basis. When
applied to diverse ground state data the QMC EDF already produces, in its
present simple form, overall agreement with experiment of a quality comparable
to a representative Skyrme EDF. There exist however multiple Skyrme paramater
sets, frequently tailored to describe selected nuclear phenomena. The QMC EDF
set of fewer parameters, as derived in this work, is not open to such
variation, chosen set being applied, without adjustment, to both the properties
of finite nuclei and nuclear matter.Comment: 9 pages, 1 table, 4 figures; in print in Phys. Rev. Letters. A minor
change in the abstract, a few typos corrected and some small technical
adjustments made to comply with the journal regulation
Fock terms in the quark-meson coupling model
The mean field description of nuclear matter in the quark-meson coupling
model is improved by the inclusion of exchange contributions (Fock terms). The
inclusion of Fock terms allows us to explore the momentum dependence of
meson-nucleon vertices and the role of pionic degrees of freedom in matter. It
is found that the Fock terms maintain the previous predictions of the model for
the in-medium properties of the nucleon and for the nuclear incompressibility.
The Fock terms significantly increase the absolute values of the
single-particle, four-component scalar and vector potentials, a feature that is
relevant for the spin-orbit splitting in finite nuclei.Comment: RevTex, 17 pages, 4 Postscript figures, version to appear in Nucl.
Phys.
In-medium Properties of as a KN structure in Relativistic Mean Field Theory
The properties of nuclear matter are discussed with the relativistic
mean-field theory (RMF).Then, we use two models in studying the in-medium
properties of : one is the point-like in the usual RMF and
the other is a KN structure for the pentaquark. It is found that the
in-medium properties of are dramatically modified by its internal
structure. The effective mass of in medium is, at normal nuclear
density, about 1030 MeV in the point-like model, while it is about 1120 MeV in
the model of KN pentaquark. The nuclear potential depth of in
the KN model is approximately -37.5 MeV, much shallower than -90 MeV in
the usual point-like RMF model.Comment: 8 pages, 5 figure
Scalar susceptibility and chiral symmetry restoration in nuclei
We study the nuclear modification of the scalar QCD susceptibility,
calculated as the derivative of the quark condensate with respect to the quark
mass. We show that it has two origins. One is the low lying nuclear
excitations. At normal nuclear density this part is constrained by the nuclear
incompressibility. The other part arises from the individual nucleon response
and it is dominated by the pion cloud contribution. Numerically the first
contribution dominates. The resulting increase in magnitude of the scalar
susceptibility at normal density is such that it becomes close to the
pseudoscalar susceptibility, while it is quite different in the vacuum. We
interpret it as a consequence of chiral symmetry restoration in nuclei.Comment: 17 pages, 5 figure
Chiral symmetry and quantum hadro-dynamics
Using the linear sigma model, we study the evolutions of the quark condensate
and of the nucleon mass in the nuclear medium. Our formulation of the model
allows the inclusion of both pion and scalar-isoscalar degrees of freedom. It
guarantees that the low energy theorems and the constrains of chiral
perturbation theory are respected. We show how this formalism incorporates
quantum hadro-dynamics improved by the pion loops effects.Comment: 24 pages, 2 figure
Effect of the bound nucleon form factors on charged-current neutrino-nucleus scattering
We study the effect of bound nucleon form factors on charged-current
neutrino-nucleus scattering. The bound nucleon form factors of the vector and
axial-vector currents are calculated in the quark-meson coupling model. We
compute the inclusive C() cross sections using a
relativistic Fermi gas model with the calculated bound nucleon form factors.
The effect of the bound nucleon form factors for this reaction is a reduction
of 8% for the total cross section, relative to that calculated with the
free nucleon form factors.Comment: Latex, 11 pages, 3 figures, version to appear in Phys. Rev. C (Brief
Report
Quark-meson coupling model with constituent quarks: Exchange and pionic effects
The binding energy of nuclear matter including exchange and pionic effects is
calculated in a quark-meson coupling model with massive constituent quarks. As
in the case with elementary nucleons in QHD, exchange effects are repulsive.
However, the coupling of the mesons directly to the quarks in the nucleons
introduces a new effect on the exchange energies that provides an extra
repulsive contribution to the binding energy. Pionic effects are not small.
Implications of such effects on observables are discussed.Comment: 12 pages, latex, 1 figure, to appear in Phys. Lett.
Droplet formation in cold asymmetric nuclear matter in the quark-meson-coupling model
The quark-meson-coupling model is used to study droplet formation from the
liquid-gas phase transition in cold asymmetric nuclear matter. The critical
density and proton fraction for the phase transition are determined in the mean
field approximation. Droplet properties are calculated in the Thomas-Fermi
approximation. The electromagnetic field is explicitly included and its effects
on droplet properties are studied. The results are compared with the ones
obtained with the NL1 parametrization of the non-linear Walecka model.Comment: 21 pages, RevTeX including 8 figures in .eps file
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