State Of Asymmetric Nuclear Matter Research Articles

Decomposition of the equation of state of asymmetric nuclear matter into different spin-isospin channels

We investigate the equation of state of asymmetric nuclear matter and its isospin dependence in various spin-isospin ST channels within the framework of the Brueckner–Hartree–Fock approach extended to include a microscopic three-body force (TBF). It is shown that the potential energy per nucleon in the isospin-singlet T = 0 channel is mainly determined by the contribution from the tensor SD coupled channel. At high densities, the TBF effect on the isospin-triplet T = 1 channel contribution turns out to be much larger than that on the T = 0 channel contribution. At low densities around and below the normal nuclear matter density, the isospin dependence is found to come essentially from the isospin-singlet SD channel and the isospin-triplet T = 1 component is almost independent of isospin asymmetry. As the density increases, the T = 1 channel contribution becomes sensitive to the isospin asymmetry and at high enough densities its isospin dependence may even become more pronounced than that of the T = 0 contribution. The present results may provide some microscopic constraints for improving effective nucleon-nucleon interactions in a nuclear medium and for constructing new functionals of effective nucleon-nucleon interaction based on microscopic many-body theories.

Nuclear matter at a HIRFL-CSR energy regime

We report some recent progress in constraining the symmetry energy Esym(ρ) at high densities using high-energy heavy-ion collisions. Circumstantial evidence of a soft Esym(ρ) at supra-saturation density is obtained by comparing the pion ratio π−/π+ measured recently with FOPI at GSI and the IBUU04 model calculations. Detailed studies indicate that the power of determining the Esym(ρ) from π−/π+ is enhanced with decreasing the beam energy to near the pion production threshold, showing a correlation to the increasing nuclear stopping. Among several heavy-ion reaction facilities in the world, the cooling storage ring (HIRFL-CSR), newly commissioned at Lanzhou, delivering heavy-ion beams up to 1 A GeV, to be coupled with advanced detectors will contribute significantly to further studies of the equation of state of asymmetric nuclear matter.

Locating the inner edge of the neutron star crust using terrestrial nuclear laboratory data

Within both dynamical and thermodynamical approaches using the equation of state for neutron-rich nuclear matter constrained by the recent isospin diffusion data from heavy-ion reactions in the same subsaturation density range as the neutron star crust, the density and pressure at the inner edge separating the liquid core from the solid crust of neutron stars are determined to be $0.040 {\mathrm{fm}}^{\ensuremath{-}3}\ensuremath{\leqslant}{\ensuremath{\rho}}_{t}\ensuremath{\leqslant}0.065 {\mathrm{fm}}^{\ensuremath{-}3}$ and 0.01 MeV/${\mathrm{fm}}^{3}\ensuremath{\leqslant}{P}_{t}\ensuremath{\leqslant}0.26$ MeV/${\mathrm{fm}}^{3}$, respectively. These together with the observed minimum crustal fraction of the total moment of inertia allow us to set a new limit for the radius of the Vela pulsar significantly different from the previous estimate. It is further shown that the widely used parabolic approximation to the equation of state of asymmetric nuclear matter leads systematically to significantly higher core-crust transition densities and pressures, especially with stiffer symmetry energy functionals.

Hot Nuclear Matter Equation of State and Finite Temperature Kaon Condensation

We perform a systematic calculation of the equation of state of asymmetric nuclear matter at finite temperature within the framework of the Brueckner–Hartree–Fock approach with a microscopic three-body force. When applying it to the study of hot kaon condensed matter, we find that the thermal effect is more profound in comparison with normal matter, in particular around the threshold density. Also, the increase of temperature makes the equation of state slightly stiffer through suppression of kaon condensation.

Symmetry Energy and Isovector Giant Dipole Resonance in Finite Nuclei

We study the relationship between the properties of the isovector giant dipole resonance of finite nuclei and the symmetry energy in the framework of the relativistic mean field theory with six different parameter sets of nonlinear effective Lagrangian. A strong linear correlation of excited energies of the dipole resonance in finite nuclei and symmetry energy at and below the saturation density is found. This linear correlation leads to the symmetry energy at the saturation density at the interval 33.0MeV ⩽ S(ρo) ⩽37.0MeV. The comparison to the present experimental data in the soft dipole mode of 132Sn constrains approximately the symmetry energy at p = 0.1 fm−3 at the interval 21.2 MeV ∼ 22.5 MeV. It is proposed that a precise measurement of the soft dipole mode in neutron rich nuclei could set up an important constraint on the equation of state for asymmetric nuclear matter.

Validating relativistic models of nuclear structure against theoretical, experimental, and observational constraints

Relativistic mean-field models of nuclear structure have been enormously successful at reproducing ground-state properties of finite nuclei throughout the periodic table using a handful of accurately calibrated parameters. In this contribution, we use powerful theoretical, experimental, and observational constraints on the equation of state of asymmetric nuclear matter--not employed in the calibration procedure--to validate two such models: NL3 and FSUGold. It is observed that FSUGold is consistent with all these constraints, except perhaps for a high-density equation of state that appears mildly softer than required by astronomical observations. It is argued that incorporating such constraints goes a long way in removing much of the ambiguity left over from the standard calibrating procedure.

Isotope analysis in central heavy ion collisions at intermediate energies

Symmetry energy is a key quantity in the study of the equation of state of asymmetric nuclear matter. Heavy ion collisions at low and intermediate energies, performed at Laboratori Nazionali di Legnaro and Laboratori Nazionali del Sud, can be used to extract information on the symmetry energy coefficient Csym, which is currently poorly known but relevant both for astrophysics and for structure of exotic nuclei.

Nuclear mean field and equation of state of asymmetric nuclear matter

Neutron and proton mean field properties and equation of state of highly isospin asymmetric dense nuclear matter are studied using simple finite range effective interactions. The density dependence of nuclear symmetry energy is constrained on the basis of an approximate universal high density behaviour of asymmetric contribution to the nucleonic part of energy density of infinite n + p + e + μ matter in beta-equilibrium. Recently discovered astrophysical bounds from neutron star mass measurements and cooling phenomenology as well as informations coming from optical model analysis of nucleon–nucleus scattering data at intermediate energies, transport model analysis of flow data in heavy ion collisions and monopole mode of vibrations in finite nuclei have also been used to constrain the interaction parameters involved.

Constraining the density dependence of the symmetry energy in the nuclear equation of state using heavy ion beams

The density dependence of the symmetry energy in the equation of state of asymmetric nuclear matter (N/Z>1) is important for understanding the structure of systems as diverse as the atomic nuclei and neutron stars. Due to a lack of understanding of the basic nucleon–nucleon interaction for matter that is highly asymmetric and at non-normal nuclear density, this very important quantity has remained largely unconstrained. Recent studies using beams from the Cyclotron Institute of Texas A&M University constrain the density dependence of the symmetry energy. A dependence of the form Esym(ρ)=C(ρ/ρo)γ, where C=31.6MeV and γ=0.69, is obtained. Their implications to both astrophysical and nuclear physics studies are discussed.

Evidence for Strong Dominance of Proton-Neutron Correlations in Nuclei

We analyze recent data from high-momentum-transfer (p, pp) and (p, ppn) reactions on carbon. For this analysis, the two-nucleon short-range correlation (NN-SRC) model for backward nucleon emission is extended to include the motion of the NN pair in the mean field. The model is found to describe major characteristics of the data. Our analysis demonstrates that the removal of a proton from the nucleus with initial momentum 275-550 MeV/c is 92(+8/-18) % of the time accompanied by the emission of a correlated neutron that carries momentum roughly equal and opposite to the initial proton momentum. This indicates that the probabilities of pp or nn SRCs in the nucleus are at least a factor of 6 smaller than that of pn SRCs. Our result is the first estimate of the isospin structure of NN-SRCs in nuclei, and may have important implication for modeling the equation of state of asymmetric nuclear matter.

Asymmetrical nuclear matter calculations with the new charge-dependent Reid potential

We calculate the equation of state for asymmetric nuclear matter with the new charge-dependent Reid potential (Reid93) within the lowest order constrained variational method (LOCV) for the wide range of densities and proton to neutron ratio ( R ). Like our previous work on the symmetrical nuclear matter, it is found that the Reid93 potential over binds the asymmetrical nuclear matter with respect to other potentials at same density and R ratio. The symmetry energy of about 50 MeV is obtained at the saturation density. Various properties of the asymmetrical nuclear matter such as the symmetry energy, validity of α 2 law, etc., are examined and the results are compared with the others many-body calculations.

Momentum and density dependence of the isospin part of nuclear mean field and equation of state of asymmetric nuclear matter

Momentum and density dependence of the isospin part of nuclear mean field u τ ( k , ρ ) which is still, in part, the open problem of the old Lane potential is analysed using density dependent finite range effective interactions. The behaviour of u τ ( k = k f , ρ ) around the Fermi momentum k f is found to be related to the density dependence of nuclear symmetry energy J τ ( ρ ) and nucleon effective mass M ∗ ( k = k f , ρ ) / M in symmetric nuclear matter. The momentum dependence of u τ ( k , ρ ) is separated out in terms of a simple functional u τ e x ( k , ρ ) which vanishes at k = k f and involves only the finite range parts of the exchange interactions between pairs of like and unlike nucleons. Depending on the choice of the parameters of these exchange interactions two conflicting trends of momentum dependence are noticed which lead to two opposite types of splitting of neutron and proton effective masses. The equation of state of asymmetric nuclear matter and the high density behaviour of nuclear symmetry energy J τ ( ρ ) are studied by constraining the additional parameters involved on the basis that pure neutron matter should not be predicted to be bound by any reasonable nuclear interaction. Emphasis is also given on the need of experimental data sensitive to the differences between neutron and proton transport properties in highly asymmetric dense nuclear matter and its analysis to constrain the high density behaviour of nuclear symmetry energy as well as to resolve the controversy on the two opposite types of splitting of neutron and proton effective masses.

Neutron star properties from an NJL model modified to simulate confinement

The NJL model has recently been extended with a method to simulate confinement. This leads in mean field approximation to a natural mechanism for the saturation of nuclear matter. We use the model to investigate the equation of state of asymmetric nuclear matter and then use it to compute the properties of neutron stars.

Equation of state in asymmetric nuclear matter(Poster presentation,YITP Workshop on New Developments in Nuclear Self-Consistent Mean-Field Theories (MF05))

Equation of state in asymmetric nuclear matter(Poster presentation,YITP Workshop on New Developments in Nuclear Self-Consistent Mean-Field Theories (MF05))

Neutron skin thickness and equation of state in asymmetric nuclear matter

The neutron skin thickness of stable and unstable nuclei is studied in Skyrme Hartree-Fock (SHF) and relativistic mean field (RMF) models to investigate the relation between the pressure and the equation of state in neutron matter. We found a clear linear correlation between the neutron skin thickness in heavy nuclei $^{132}\mathrm{Sn}$ and $^{208}\mathrm{Pb}$ and the pressure of neutron matter in both SHF and RMF models, while the correlation is weak in the unstable nuclei $^{32}\mathrm{Mg}$ and $^{44}\mathrm{Ar}$. Relations between the neutron skin thickness and other nuclear matter properties such as the symmetry energy coefficients and the nuclear incompressibility are discussed.

Variational Calculations for the Equation of State of Asymmetric Nuclear Matter

Two variational methods are used to calculate energies per nucleon of asymmetric nuclear matter. One is the explicit energy functional method, in which approximate energy expressions are proposed as explicit functionals of the variational functions. The other is the two-body cluster variational method. The numerical results show that, in both cases, the saturation densities decrease markedly as the proton fraction decreases.

Neutron densities and the equation of state for neutron-rich matter

We present predictions for energies, proton and neutron rms radii, and neutron skins of some closed-shell nuclei based upon a microscopic model of the equation of state for asymmetric nuclear matter which is used as input for a mass formula. We employ realistic two-body forces and the Dirac-Brueckner-Hartree-Fock approach to nuclear matter. We compare with experimental information, when available, and point out the need for accurate determinations of neutron densities and skins.

Warm asymmetric matter in the quark-meson coupling model

In this work we study the warm equation of state of asymmetric nuclear matter in the quark-meson coupling model which incorporates explicitly quark degrees of freedom, with quarks coupled to scalar, vector, and isovector mesons. Mechanical and chemical instabilities are discussed as a function of density and isospin asymmetry. The binodal section, essential in the study of the liquid-gas phase transition is also constructed and discussed. The main results for the equation of state are compared with two common parametrizations used in the nonlinear Walecka model and the differences are outlined.

Microscopic calculations in asymmetric nuclear matter

A microscopic calculation of the equation of state for asymmetric nuclear matter is presented. We employ realistic nucleon-nucleon forces and operate within the Dirac-Brueckner-Hartree-Fock approach to nuclear matter. The focal point of this paper is a (momentum-space) G-matrix which properly accounts for the asymmetry between protons and neutrons. This will merge naturally into the development of an effective interaction suitable for applications to asymmetric nuclei, which will be the object of extensive study in the future.

Effective Dirac Brueckner-Hartree-Fock method for asymmetric nuclear matter and finite nuclei

A new decomposition of the Dirac structure of nucleon self-energies in the Dirac Brueckner-Hartree-Fock (DBHF) approach is adopted to investigate the equation of state for asymmetric nuclear matter. The effective coupling constants of $\sigma $, $\omega $, $\delta $ and $\rho $ mesons with a density dependence in the relativistic mean field approach are deduced by reproducing the nucleon self-energy resulting from the DBHF at each density for symmetric and asymmetric nuclear matter. With these couplings the properties of finite nuclei are investigated. The agreement of charge radii and binding energies of finite nuclei with the experimental data are improved simultaneously in comparison with the projection method. It seems that the properties of finite nuclei are sensitive to the scheme used for the DBHF self-energy extraction. We may conclude that the properties of the asymmetric nuclear matter and finite nuclei could be well described by the new decomposition approach of the G matrix.