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 $\delta$ 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 $\beta$-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 $\sigma$-$\omega$ 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($\sigma_{np}^{*}$, $\sigma_{pp(nn)}^{*}$) 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 $\rho$ meson field. The medium correction of nucleon-nucleon scattering cross sections is also isospin dependent, $\sigma_{np}^{*}$ depends on the baryon density weakly and $\sigma_{pp(nn)}^{*}$ depends on the baryon density significantly, which is due to the different effects of the medium correction of nucleon mass and $\rho$ meson mass on $\sigma_{np}$ and $\sigma_{pp(nn)}$, 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