368 research outputs found
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
Cold uniform matter and neutron stars in the quark-mesons-coupling model
A new density dependent effective baryon-baryon interaction has been recently
derived from the quark-meson-coupling (QMC) model, offering impressive results
in application to finite nuclei and dense baryon matter. This self-consistent,
relativistic quark-level approach is used to construct the Equation of State
(EoS) and to calculate key properties of high density matter and cold, slowly
rotating neutron stars. The results include predictions for the maximum mass of
neutron star models, together with the corresponding radius and central
density, as well the properties of neutron stars with mass of order 1.4
. The cooling mechanism allowed by the QMC EoS is explored and the
parameters relevant to slow rotation, namely the moment of inertia and the
period of rotation investigated. The results of the calculation, which are
found to be in good agreement with available observational data, are compared
with the predictions of more traditional EoS. The QMC EoS provides cold neutron
star models with maximum mass 1.9--2.1 M, with central density less
than 6 times nuclear saturation density () and
offers a consistent description of the stellar mass up to this density limit.
In contrast with other models, QMC predicts no hyperon contribution at
densities lower than , for matter in -equilibrium. At higher
densities, and hyperons are present
Nucleon form factors and moments of parton distributions in twisted mass lattice QCD
We present results on the electroweak form factors and on the lower moments
of parton distributions of the nucleon, within lattice QCD using two dynamical
flavors of degenerate twisted mass fermions. Results are obtained on lattices
with three different values of the lattice spacings, namely a=0.089 fm, a=0.070
fm and a=0.056 fm, allowing the investigation of cut-off effects. The volume
dependence is examined by comparing results on two lattices of spatial length
L=2.1 fm and L=2.8 fm. The simulations span pion masses in the range of 260-470
MeV. Our results are renormalized non-perturbatively and the values are given
in the MS-scheme at a scale mu=2 GeV.Comment: Talk presented in the XXIst International Europhysics Conference on
High Energy Physics, 21-27 July 2011, Grenoble, Rhones Alpes Franc
Hartree-Fock Formulation of the QMC Model at Finite Temperature
We present, for the first time, a detailed theory of high density matter
including the entire baryon octet at finite temperature, based on a fully
relativistic mean field model with a consistent treatment of exchange (Fock)
terms, using the quark-meson-coupling model (QMC). It has been already
demonstrated that the QMC equation of state is applicable in thermodynamic
scenarios in stationary and rotating isentropic proto-neutron stars, producing
results in agreement with recent observation. It is also suitable for the
simulation of the behavior following a binary neutron star merger [1];
https://compose.obspm.fr/eos/205. We develop a comprehensive demonstration of
the impact of the Fock terms in the QMC energy density functional on properties
of neutrinoless proto-neutron stars with cores containing the full hyperon
octet with constant entropy, S/A=2kB. Given the interest in the properties of
the proto-neutron star remaining after either a supernova explosion or the
merger of two neutron stars, it is vital to develop modern equations of state
at finite temperature. While much attention has been paid to relativistic
mean-field calculations at finite temperature, it is crucial to explore the
consequences of a consistent treatment of the Fock terms
The extended, relativistic hyperon star model
In this paper an equation of state of neutron star matter which includes
strange baryons in the framework of Zimanyi and Moszkowski (ZM) model has been
obtained. We concentrate on the effects of the isospin dependence of the
equation of state constructing for the appropriate choices of parameters the
hyperons star model. Numerous neutron star models show that the appearance of
hyperons is connected with the increasing density in neutron star interiors.
Various studies have indicated that the inclusion of delta meson mainly affects
the symmetry energy and through this the chemical composition of a neutron
star. As the effective nucleon mass contributes to hadron chemical potentials
it alters the chemical composition of the star. In the result the obtained
model of the star not only excludes large population of hadrons but also does
not reduce significantly lepton contents in the star interior.Comment: 22 pages, revtex4, 13 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
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
Dispersion relation formalism for virtual Compton scattering and the generalized polarizabilities of the nucleon
A dispersion relation formalism for the virtual Compton scattering (VCS)
reaction on the proton is presented, which for the first time allows a
dispersive evaluation of 4 generalized polarizabilities at a four-momentum
transfer 0.5 GeV. The dispersive integrals are calculated using
a state-of-the-art pion photo- and electroproduction analysis. The dispersion
formalism provides a new tool to analyze VCS experiments above pion threshold,
thus increasing the sensitivity to the generalized polarizabilities of the
nucleon.Comment: 4 pages, 2 figure
Quark mean field model with density dependent couplings for finite nuclei
The quark mean field model, which describes the nucleon using the constituent
quark model, is applied to investigate the properties of finite nuclei. The
couplings of the scalar and vector mesons with quarks are made density
dependent through direct coupling to the scalar field so as to reproduce the
relativistic Brueckner-Hartree-Fock results of nuclear matter. The present
model provides satisfactory results on the properties of spherical nuclei, and
predicts an increasing size of the nucleon as well as a reduction of the
nucleon mass in the nuclear environmentComment: 8 pages, REVTeX, 8 ps figures, accepted for publication in Phys. Rev.
- …