49 research outputs found
Relativistic model for nuclear matter and atomic nuclei with momentum-dependent self-energies
The Lagrangian density of standard relativistic mean-field (RMF) models with
density-dependent meson-nucleon coupling vertices is modified by introducing
couplings of the meson fields to derivative nucleon densities. As a
consequence, the nucleon self energies, that describe the effective in-medium
interaction, become momentum dependent. In this approach it is possible to
increase the effective (Landau) mass of the nucleons, that is related to the
density of states at the Fermi energy, as compared to conventional relativistic
models. At the same time the relativistic effective (Dirac) mass is kept small
in order to obtain a realistic strength of the spin-orbit interaction.
Additionally, the empirical Schroedinger-equivalent central optical potential
from Dirac phenomenology is reasonably well described. A parametrization of the
model is obtained by a fit to properties of doubly magic atomic nuclei. Results
for symmetric nuclear matter, neutron matter and finite nuclei are discussed.Comment: 14 pages, 7 figures, 5 tables, extended introduction and conclusions,
additional references, minor corrections, accepted for publication in Phys.
Rev.
Hyperons in a relativistic mean-field approach to asymmetric nuclear matter
Relativistic mean-field theory with meson, nonlinear isoscalar
self-interactions and isoscalar-isovector cross interaction terms with
parametrizations obtained to reproduce Dirac-Brueckner-Hartree-Fock
calculations for nuclear matter is used to study asymmetric nuclear matter
properties in -equilibrium, including hyperon degrees of freedom and
(hidden) strange mesons. Influence of cross interaction on composition of
hyperon matter and electron chemical potential is examined. Softening of
nuclear equation of state by the cross interactions results in lowering of
hyperonization, although simultaneously enhancing a hyperon-induced decrease of
the electron chemical potential, thus indicating further shift of a kaon
condensate occurence to higher densities.Comment: 11 pages, 7 figures, 3 tables, published in Phys. Rev.
Theoretical Aspects of Science with Radioactive Nuclear Beams
Physics of radioactive nuclear beams is one of the main frontiers of nuclear
science today. Experimentally, thanks to technological developments, we are on
the verge of invading the territory of extreme N/Z ratios in an unprecedented
way. Theoretically, nuclear exotica represent a formidable challenge for the
nuclear many-body theories and their power to predict nuclear properties in
nuclear terra incognita. It is important to remember that the lesson learned by
going to the limits of the nuclear binding is also important for normal nuclei
from the neighborhood of the beta stability valley. And, of course, radioactive
nuclei are crucial astrophysically; they pave the highway along which the
nuclear material is transported up in the proton and neutron numbers during the
complicated synthesis process in stars.Comment: 26 ReVTeX pages, 11 Postscript figures, uses epsf.sty, to be
published in: Theme Issue on Science with Beams of Radioactive Nuclei,
Philosophical Transactions, ed. by W. Gelletl
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
Derivative-Coupling Models and the Nuclear-Matter Equation of State
The equation of state of saturated nuclear matter is derived using two
different derivative-coupling Lagrangians. We show that both descriptions are
equivalent and can be obtained from the sigma-omega model through an
appropriate rescaling of the coupling constants. We introduce generalized forms
of this rescaling to study the correlations amongst observables in infinite
nuclear matter, in particular, the compressibility and the effective nucleon
mass.Comment: 16 pages, 6 figures, 36 kbytes. To appear in Zeit. f. Phys. A
(Hadrons and Nuclei
Momentum-Dependent Mean Field Based Upon the Dirac-Brueckner Approach for Nuclear Matter
A momentum-dependent mean field potential, suitable for application in the
transport-model description of nucleus-nucleus collisions, is derived in a
microscopic way. The derivation is based upon the Bonn meson-exchange model for
the nucleon-nucleon interaction and the Dirac-Brueckner approach for nuclear
matter. The properties of the microscopic mean field are examined and compared
with phenomenological parametrizations which are commonly used in
transport-model calculations.Comment: 15 pages text (RevTex) and 4 figures (postscript in a separate
uuencoded file), UI-NTH-930
Self-Consistent Relativistic Calculation of Nucleon Mean Free Path
We present a fully self-consistent and relativistic calculation of the
nucleon mean free path in nuclear matter and finite nuclei. Starting from the
Bonn potential, the Dirac-Brueckner-Hartree-Fock results for nuclear matter are
parametrized in terms of an effective - Lagrangian suitable for
the relativistic density-dependent Hartree-Fock (RDHF) approximation. The
nucleon mean free path in nuclear matter is derived from this effective
Lagrangian taking diagrams up to fourth-order into account. For the nucleon
mean free path in finite nuclei, we make use of the density determined by the
RDHF calculation in the local density approximation. Our microscopic results
are in good agreement with the empirical data and predictions by Dirac
phenomenology.Comment: 16 pages RevTex and 6 figures (paper, available upon request from
[email protected]) UI-NTH-931
Isospin Dependence of Nucleon-Nucleon Elastic Cross Section
The in-medium neutron-proton, proton-proton(neutron-neutron) scattering cross
sections(, ) are studied based on QHD-II
type Lagrangian within the framework of the microscopic transport theory. The
results demonstrate that, for free nucleon-nucleon scattering cross sections,
the isospin dependence is dominantly caused by meson field. The medium
correction of nucleon-nucleon scattering cross sections is also isospin
dependent, depends on the baryon density weakly and
depends on the baryon density significantly, which is due
to the different effects of the medium correction of nucleon mass and
meson mass on and , respectivelyComment: PDF fil
Phase Transitions in Warm, Asymmetric Nuclear Matter
A relativistic mean-field model of nuclear matter with arbitrary proton
fraction is studied at finite temperature. An analysis is performed of the
liquid-gas phase transition in a system with two conserved charges (baryon
number and isospin) using the stability conditions on the free energy, the
conservation laws, and Gibbs' criteria for phase equilibrium. For a binary
system with two phases, the coexistence surface (binodal) is two-dimensional.
The Maxwell construction through the phase-separation region is discussed, and
it is shown that the stable configuration can be determined uniquely at every
density. Moreover, because of the greater dimensionality of the binodal
surface, the liquid-gas phase transition is continuous (second order by
Ehrenfest's definition), rather than discontinuous (first order), as in
familiar one-component systems. Using a mean-field equation of state calibrated
to the properties of nuclear matter and finite nuclei, various phase-separation
scenarios are considered. The model is then applied to the liquid-gas phase
transition that may occur in the warm, dilute matter produced in energetic
heavy-ion collisions. In asymmetric matter, instabilities that produce a
liquid-gas phase separation arise from fluctuations in the proton concentration
(chemical instability), rather than from fluctuations in the baryon density
(mechanical instability).Comment: Postscript file, 50 pages including 23 figure
The nucleon and mesons effective masses in the Relativistic Mean-Field Theory
Nucleon and meson effective masses in the nonlinear Relativistic Mean - Field
Theory (RMF) introducing a nonlinear omega - rho and sigma coupling motivated
by the Quark Meson Coupling model (QMC) is explored. It is shown that, in
contrast to the usual Walecka model, not only the effective nucleon mass
m_{eff,N} but also the effective sigma, rho meson masses (m_{eff, sigma},
m_{eff, rho}) and the effective omega meson mass m_{eff, omega} are nucleon
density dependent.Comment: 11 pages, iop latex2e, 7 colour figures, revised version of
nucl-th/0011084, accepted to Journal of Physics G: Nuclear and Particle,
presented on "Mesons & Light Nuclei '01", Prague, June 200