Showing papers on "Nuclear matter published in 2005"
TL;DR: A review of recent applications of self-consistent relativistic mean field models to exotic nuclear structure can be found in this article, where the authors provide a rich theoretical framework for studies of nuclei along the valley of β-stability, exotic nuclei with extreme groundstate isospin values and close to the particle drip lines.
782 citations
TL;DR: In this article, the authors give an overview of all these striking physical possibilities, with an emphasis on the astrophysical phenomenology of strange quark matter, and discuss possible observational signatures associated with the theoretically proposed states of matter inside compact stars, and provide most valuable information about the phase diagram of superdense nuclear matter at high baryon number density but low temperature.
674 citations
TL;DR: The monopole effect of the tensor force is presented, exhibiting how spherical single-particle energies are shifted as protons or neutrons occupy certain orbits.
Abstract: The monopole effect of the tensor force is presented, exhibiting how spherical single-particle energies are shifted as protons or neutrons occupy certain orbits. An analytic relation for such shifts is shown, and their general features are explained intuitively. Single-particle levels are shown to change in a systematic and robust way, by using the $\ensuremath{\pi}+\ensuremath{\rho}$ meson exchange tensor potential, consistently with the chiral perturbation idea. Several examples are compared with experiments.
596 citations
TL;DR: In this paper, it was shown that a hybrid (nuclear+quark matter) star can have a mass-radius relationship very similar to that predicted for a star made of purely nucleonic matter.
Abstract: We show that a hybrid (nuclear+quark matter) star can have a mass-radius relationship very similar to that predicted for a star made of purely nucleonic matter. We show this for a generic parameterization of the quark matter equation of state and also for an MIT bag model, each including a phenomenological correction based on gluonic corrections to the equation of state. We obtain hybrid stars as heavy as 2 M☉ for reasonable values of the bag model parameters. For nuclear matter, we use the equation of state calculated by Akmal and coworkers using many-body techniques. Both mixed and homogeneous phases of nuclear and quark matter are considered.
571 citations
TL;DR: In this article, the roles of isospin asymmetry in nuclei and neutron stars are investigated using a range of potential and field-theoretical models of nucleonic matter.
566 citations
TL;DR: In this paper, the results of ab initio simulations of n -rich, n -poor, heavy-ion collisions, using stochastic isospin-dependent transport equations, are analyzed as a function of beam energy and centrality.
534 citations
TL;DR: In this paper, a new improved relativistic mean-field effective interaction with explicit density dependence of the meson-nucleon couplings was proposed. But it was only applied to the analysis of very recent data on superheavy nuclei.
Abstract: We adjust a new improved relativistic mean-field effective interaction with explicit density dependence of the meson-nucleon couplings. The effective interaction DD-ME2 is tested in relativistic Hartree-Bogoliubov and quasiparticle random-phase approximation (QRPA) calculations of nuclear ground states and properties of excited states, in calculation of masses, and it is applied to the analysis of very recent data on superheavy nuclei.
526 citations
TL;DR: An accurately calibrated relativistic parametrization is introduced to compute the ground state properties of finite nuclei, their linear response, and the structure of neutron stars, and it produces an equation of state that is considerably softer--both for symmetric nuclear matter and for the symmetry energy.
Abstract: An accurately calibrated relativistic parametrization is introduced to compute the ground state properties of finite nuclei, their linear response, and the structure of neutron stars. While similar in spirit to the successful NL3 parameter set, it produces an equation of state that is considerably softer--both for symmetric nuclear matter and for the symmetry energy. This softening appears to be required for an accurate description of several collective modes having different neutron-to-proton ratios. Among the predictions of this model are a symmetric nuclear-matter incompressibility of K=230 MeV and a neutron skin thickness in 208 Pb of Rn-Rp=0.21 fm. The impact of such a softening on various neutron-star properties is also examined.
464 citations
TL;DR: Using a momentum dependence derived from the Gogny effective interaction, recent experimental data from NSCL-MSU on isospin diffusion are shown to be consistent with a nuclear symmetry energy given by E(sym)(rho) approximately 31.6(rho/rho(0))(1.05) at subnormal densities.
Abstract: With an isospin- and momentum-dependent transport model, we find that the degree of isospin diffusion in heavy-ion collisions at intermediate energies is affected by both the stiffness of the nuclear symmetry energy and the momentum dependence of the nucleon potential. Using a momentum dependence derived from the Gogny effective interaction, recent experimental data from NSCL-MSU on isospin diffusion are shown to be consistent with a nuclear symmetry energy given by E(sym)(rho) approximately 31.6(rho/rho(0))(1.05) at subnormal densities. This leads to a significantly constrained value of about -550 MeV for the isospin-dependent part of the isobaric incompressibility of isospin asymmetric nuclear matter.
350 citations
TL;DR: In this article, the authors review the physics of nuclear matter at high energy density and the experimental search for the Quark-Gluon Plasma at the Relativistic Heavy Ion Collider (RHIC) and provide several lines of evidence that a novel state of matter has been created in the most violent head-on collisions of Au nuclei at √ s = 200 GeV.
223 citations
TL;DR: The phase structure of a dilute two-component Fermi system with attractive interactions as a function of the coupling and a finite number asymmetry or polarization is studied and a picture of weakly interacting quasiparticles emerges for modest polarizations.
Abstract: We study the phase structure of a dilute two-component Fermi system with attractive interactions as a function of the coupling and a finite number asymmetry or polarization. In weak coupling, a number asymmetry results in phase separation. A mixed phase containing symmetric superfluid matter and an asymmetric normal phase is favored. For strong coupling we show that the stress on the superfluid phase to accommodate a number asymmetry increases. Near the infinite-scattering length, we calculate the single-particle excitation spectrum and the ground-state energy. A picture of weakly interacting quasiparticles emerges for modest polarizations. In this regime a homogeneous phase with a finite population of quasiparticle states characterized by a gapless spectrum is favored over the phase separated state. These states may be realized in cold atom experiments.
TL;DR: In this paper, the authors explored the nonperturbation nature of inter-nucleon interactions by varying the momentum cutoff of a two nucleon potential and found that the softened potential combined with Pauli blocking leads to corrections in nuclear matter in the particle-particle channel that are well converged at second order in the potential, suggesting that perturbation theory can be used in place of Brueckner resummations.
TL;DR: In this paper, the Lagrangian density of standard relativistic mean field models with density-dependent meson-nucleon coupling vertices is modified by introducing couplings of the meson fields to derivative nucleon densities.
Abstract: The Lagrangian density of standard relativistic mean-field 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 to obtain a realistic strength of the spin-orbit interaction. Additionally, the empirical Schr\"odinger-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.
TL;DR: In this paper, the excitation function of elliptic flow at midrapidity in Au+Au collisions at beam energies from 0.09 to 1.49 GeV per nucleon is presented.
TL;DR: In this article, the effect of hadron structure changes in a nuclear medium using the quark-meson coupling (QMC) model is reviewed, which is based on a mean field description of non-overlapping nucleon (or baryon) bags bound by the self-consistent exchange of scalar and vector mesons.
Abstract: We review the effect of hadron structure changes in a nuclear medium using the quark-meson coupling (QMC) model, which is based on a mean field description of non-overlapping nucleon (or baryon) bags bound by the self-consistent exchange of scalar and vector mesons. This approach leads to simple scaling relations for the changes of hadron masses in a nuclear medium. It can also be extended to describe finite nuclei, as well as the properties of hypernuclei and meson-nucleus deeply bound states. It is of great interest that the model predicts a variation of the nucleon form factors in nuclear matter. We also study the empirically observed, Bloom-Gilman (quark-hadron) duality.
Other applications of the model include subthreshold kaon production in heavy ion collisions, D and D-bar meson production in antiproton-nucleus collisions, and J/Psi suppression. In particular, the modification of the D and D-bar meson properties in nuclear medium can lead to a large J/Psi absorption cross section, which explains the observed J/Psi suppression in relativistic heavy ion collisions.
TL;DR: In this paper, the density functional theory with relativistic mean fields coupled with the electric field was used to study the nonuniform structures of the nucleon matter at subnuclear densities.
Abstract: Nonuniform structures of the nucleon matter at subnuclear densities are numerically studied by means of the density functional theory with relativistic mean fields coupled with the electric field. A particular role of the charge screening effects is demonstrated.
TL;DR: It is demonstrated that the largest measured mass of a neutron star establishes an upper bound to the energy density of observable cold baryonic matter.
Abstract: We demonstrate that the largest measured mass of a neutron star establishes an upper bound to the energy density of observable cold baryonic matter. An equation of state-independent expression satisfied by both normal neutron stars and self-bound quark matter stars is derived for the largest energy density of matter inside stars as a function of their masses. The largest observed mass sets the lowest upper limit to the density. Implications from existing and future neutron star mass measurements are discussed.
TL;DR: In this article, the excitation spectrum of the nuclear pasta was computed via a molecular-dynamics simulation involving up to 100,000 nucleons and the dynamic response of the pasta displays a classical plasma oscillation in the 1-to 2-MeV region.
Abstract: The nuclear pasta---a novel state of matter having nucleons arranged in a variety of complex shapes---is expected to be found in the crust of neutron stars and in core-collapse supernovae at subnuclear densities of about ${10}^{14}$ g/cm${}^{3}$. Owing to frustration, a phenomenon that emerges from the competition between short-range nuclear attraction and long-range Coulomb repulsion, the nuclear pasta displays a preponderance of unique low-energy excitations. These excitations could have a strong impact on many transport properties, such as neutrino propagation through stellar environments. The excitation spectrum of the nuclear pasta is computed via a molecular-dynamics simulation involving up to 100,000 nucleons. The dynamic response of the pasta displays a classical plasma oscillation in the 1- to 2-MeV region. In addition, substantial strength is found at low energies. Yet this low-energy strength is missing from a simple ion model containing a single-representative heavy nucleus. The low-energy strength observed in the dynamic response of the pasta is likely to be a density wave involving the internal degrees of freedom of the clusters.
TL;DR: In this paper, the single-particle spectral functions in asymmetric nuclear matter were computed using the ladder approximation within the theory of finite temperature Green's functions, and the internal energy and the momentum distributions of protons and neutrons were studied as a function of the density and the asymmetry of the system.
Abstract: The single-particle spectral functions in asymmetric nuclear matter are computed using the ladder approximation within the theory of finite temperature Green's functions. The internal energy and the momentum distributions of protons and neutrons are studied as a function of the density and the asymmetry of the system. The proton states are more strongly depleted when the asymmetry increases whereas the occupation of the neutron states is enhanced compared to the symmetric case. The self-consistent Green's function approach leads to slightly smaller energies compared to the Brueckner-Hartree-Fock approach. This effect increases with density and thereby modifies the saturation density and leads to smaller symmetry energies.
TL;DR: In this paper, the effects from two-pion exchange with single and double virtual Δ (1232 ) -isobar excitation were investigated. And the effects of 2π-exchange with virtual Δ-excitation on the nuclear energy density functional were also investigated.
TL;DR: In this paper, the authors derived the isospin splitting of the nucleon mean field from the Brueckner theory extended to asymmetric nuclear matter, and compared the theoretical predictions with the empirical parametrizations of neutron and proton optical model potentials based on the experimental nucleon-nucleus scattering and the phenomenological ones adopted in transport model simulations of heavy-ion collisions.
Abstract: The isospin splitting of the nucleon mean field is derived from the Brueckner theory extended to asymmetric nuclear matter. The Argonne ${V}_{18}$ has been adopted as bare interaction in combination with a microscopic three-body force. The isospin splitting of the effective mass is determined from the Brueckner-Hartree-Fock self-energy: It is linear according to the Lane ansatz, such that ${m}_{n}^{*}g{m}_{p}^{*}$ for neutron-rich matter. The symmetry potential is also determined, and a comparison is made with the predictions of the Dirac-Brueckner approach and the phenomenological interactions. The theoretical predictions are also compared with the empirical parametrizations of neutron and proton optical model potentials based on the experimental nucleon-nucleus scattering and the phenomenological ones adopted in transport model simulations of heavy-ion collisions. The direct contribution of the rearrangement term due to three-body forces to the single-particle potential and symmetry potential is discussed.
TL;DR: In this paper, the authors modified their best previous HFB mass model, HFB-8, to conform to the Friedman-Pandharipande calculation of neutron matter, achieving this simply by requiring that it be consistent with a nuclear-matter symmetry coefficient of J = 30 MeV.
TL;DR: In this article, it was shown that in the limit of large jet energy loss gluon radiation determines the yield and angular distribution of | Δ φ | ⩾ π 2 dihadrons to high transverse momenta p T 2 of the associated particles.
TL;DR: In this paper, the moment of inertia of the pulsar A in the binary J0737−3039 was measured through detailed measurements of the periastron advance and the implications of such measurement for constraining the equation of state.
Abstract: The moment of inertia of the pulsar A in the neutron star binary J0737−3039 will soon be measurable through detailed measurements of the periastron advance. We present the calculation of the moment of inertia of neutron stars with the masses of the components of the binary J0737−3039 for a broad range of equations of state of dense matter, and we discuss the implications of such measurement for constraining the equation of state. An observational determination of the moment of inertia of the pulsar A in J0737−3039 with the accuracy of 10 per cent will narrow down considerably the range of viable equations of state. We also show that limits on the maximal mass of a neutron star provide a complementary set of constraints on the properties of dense nuclear matter.
TL;DR: In this article, the relativistic mean field models with hadron masses and coupling constants depending self-consistently on a scalar meson field were studied, and it was shown that by choosing properly the latter scaling functions one can stiffen or soften the equation of state at high densities and simultaneously increase the threshold density for the direct Urca process without any change of the description of nuclear matter close to the saturation density.
TL;DR: An excellent description of both spin-independent and spin-dependent quark distributions and structure functions has been obtained with a modified Nambu--Jona-Lasinio model, and it is found that the ratio g1p(A)/g1p differs significantly from unity, with the quenching caused by the nuclear medium being about twice that of the spin- independent case.
Abstract: An excellent description of both spin-independent and spin-dependent quark distributions and structure functions has been obtained with a modified Nambu-Jona-Lasinio model, which is free of unphysical thresholds for nucleon decay into quarks--hence incorporating an important aspect of confinement. We utilize this model to investigate nuclear medium modifications to structure functions and find that we are readily able to reproduce both nuclear matter saturation and the experimental F{sub 2N}{sup A}/F{sub 2N} ratio, that is, the European Muon Collaboration (EMC) effect. Applying this framework to determine g{sub 1p}{sup A}, we find that the ratio g{sub 1p}{sup A}/g{sub 1p} differs significantly from unity, with the quenching caused by the nuclear medium being about twice that of the spin-independent case. This represents an exciting result, which, if confirmed experimentally, will reveal much about the quark structure of nuclear matter.
TL;DR: In this paper, the production/absorption rate of particles in compressed and heated asymmetric matter is studied using a Relativistic Mean Field (RMF) transport model with an isospin-dependent collision term.
TL;DR: In this paper, the half-lives of spherical nuclei away from the proton drip line by proton emissions are estimated theoretically, and the quantum mechanical tunneling probability is calculated within the WKB approximation.
Abstract: Half-lives of the decays of spherical nuclei away from the proton drip line by proton emissions are estimated theoretically. The quantum mechanical tunneling probability is calculated within the WKB approximation. Microscopic proton-nucleus interaction potentials are obtained by single folding the densities of the daughter nuclei with M3Y effective interaction supplemented by a zero-range pseudopotential for exchange along with the density dependence. Parameters of the density dependence are obtained from the nuclear matter calculations. Spherical charge distributions are used for Coulomb interaction potentials. These calculations provide reasonable estimates for the observed proton-radioactivity lifetimes of proton-rich nuclei for proton emissions from 26 ground and isomeric states of spherical proton emitters.
TL;DR: In this article, the effects of the density-dependent symmetry potential for baryons and of the Coulomb potential for produced mesons are investigated for neutron-rich heavy ion collisions at intermediate energies.
Abstract: Based on the ultrarelativistic quantum molecular dynamics model, the effects of the density-dependent symmetry potential for baryons and of the Coulomb potential for produced mesons are investigated for neutron-rich heavy ion collisions at intermediate energies. The calculated results of the Δ−/Δ++ and π−/π+ production ratios show a clear beam-energy dependence on the density-dependent symmetry potential, which is stronger for the π−/π+ ratio close to the pion production threshold. The Coulomb potential of the mesons changes the transverse momentum distribution of the π−/π+ ratio significantly, though it alters only slightly the π− and π+ total yields. The π− yields, especially at midrapidity or at low transverse momenta and the π−/π+ ratios at low transverse momenta are shown to be sensitive probes of the density-dependent symmetry potential in dense nuclear matter. The effect of the density-dependent symmetry potential on the production of both K0 and K+ mesons is also investigated.