Showing papers on "Nuclear matter published in 2004"
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 analysed as a function of beam energy and centrality.
Abstract: We review the new possibilities offered by the reaction dynamics of asymmetric heavy ion collisions, using stable and unstable beams. We show that it represents a rather unique tool to probe regions of highly Asymmetric Nuclear Matter ($ANM$) in compressed as well as dilute phases, and to test the in-medium isovector interaction for high momentum nucleons. The focus is on a detailed study of the symmetry term of the nuclear Equation of State ($EOS$) in regions far away from saturation conditions but always under laboratory controlled conditions.
Thermodynamic properties of $ANM$ are surveyed starting from nonrelativistic and relativistic effective interactions. In the relativistic case the role of the isovector scalar $\delta$-meson is stressed. The qualitative new features of the liquid-gas phase transition, "diffusive" instability and isospin distillation, are discussed. The results of ab-initio simulations of n-rich, n-poor, heavy ion collisions, using stochastic isospin dependent transport equations, are analysed as a function of beam energy and centrality. The isospin dynamics plays an important role in all steps of the reaction, from prompt nucleon emissions to the final fragments. The isospin diffusion is also of large interest, due to the interplay of asymmetry and density gradients. In relativistic collisions, the possibility of a direct study of the covariant structure of the effective nucleon interaction is shown. Results are discussed for particle production, collective flows and iso-transparency.
Perspectives of further developments of the field, in theory as well as in experiment, are presented.
454 citations
TL;DR: In this paper, the authors apply the self-consistent Green's functions to nuclei and nuclear matter to determine one and two-nucleon removal probabilities in nuclei since the corresponding amplitudes are directly related to the imaginary parts of the single particle and twoparticle propagators.
409 citations
TL;DR: In this paper, the Lagrangian density in the relativistic mean field (RMF) theory has been modeled in a microscopic way, which is essential to unify the description of nuclei from light to heavy regions with one effective interaction.
Abstract: New parameter sets for the Lagrangian density in the relativistic mean field (RMF) theory, PK1 with nonlinear sigma- and omega-meson self-coupling, PK1R with nonlinear sigma-, omega-, and rho-meson self-coupling, and PKDD with the density-dependent meson-nucleon coupling are proposed. They are able to provide an excellent description not only for the properties of nuclear matter but also for the nuclei in and far from the valley of beta stability. For the first time in the parametrization of the RMF Lagrangian density, the center-of-mass correction is treated by a microscopic way, which is essential to unify the description of nuclei from light to heavy regions with one effective interaction.
313 citations
TL;DR: The medium size dependence of heavy-quark energy loss is found to change from a linear to a quadratic form when the initial energy and momentum scale are increased relative to the quark mass.
Abstract: Multiple scattering, modified fragmentation functions and radiative energy loss of a heavy quark propagating in a nuclear medium are investigated in perturbative QCD Because of the quark mass dependence of the gluon formation time, the medium size dependence of heavy quark energy loss is found to change from a linear to a quadratic form when the initial energy and momentum scale are increased relative to the quark mass The radiative energy loss is also significantly suppressed relative to a light quark due to the suppression of collinear gluon emission by a heavy quark
238 citations
TL;DR: The polarization contributions to second order in the low-momentum interaction V(low k) are computed and it is found that the medium-induced spin-orbit interaction leads to a reduction of the 3P2 pairing gap for neutrons in the interior of neutron stars.
Abstract: We calculate the modification of the effective interaction of particles on the Fermi surface due to polarization contributions, with particular attention to spin-dependent forces. In addition to the standard spin-spin, tensor, and spin-orbit forces, spin nonconserving effective interactions are induced by screening in the particle-hole channels. Furthermore, a novel long-wavelength tensor force is generated. We compute the polarization contributions to second order in the low-momentum interaction V l o w k and find that the medium-induced spin-orbit interaction leads to a reduction of the 3 P 2 pairing gap for neutrons in the interior of neutron stars.
130 citations
TL;DR: In this article, the properties of asymmetric nuclear matter have been investigated in a relativistic Dirac-Brueckner-Hartree-Fock framework using the Bonn A potential.
123 citations
TL;DR: In this paper, the authors calculate the nucleonic equation of state within the Brueckner-Bethe-Goldstone formalism using the Argonne ${\ensuremath{\upsilon}}_{18}$ two-body interaction and a threebody interaction.
Abstract: We calculate the nucleonic equation of state within the Brueckner-Bethe-Goldstone formalism using the Argonne ${\ensuremath{\upsilon}}_{18}$ two-body interaction and a three-body interaction We adopt two different three-body forces: the phenomenological Urbana IX model and a microscopic meson-exchange force including nucleon virtual excitations and nucleon-antinucleon excitations We compare their respective predictions regarding the structure of neutron stars, in particular the mass-radius relation
114 citations
TL;DR: In this paper, the static structure factor is calculated from molecular dynamics simulations involving 40, 000 to 100, 000 nucleons, and the neutrino opacities are then calculated within a single heavy nucleus approximation.
Abstract: Nonuniform neutron-rich matter present in both core-collapse supernovae and neutron-star crusts is described in terms of a semiclassical model that reproduces nuclear-matter properties and includes long-range Coulomb interactions. The neutron-neutron correlation function and the corresponding static structure factor are calculated from molecular dynamics simulations involving 40 000 to 100 000 nucleons. The static structure factor describes coherent neutrino scattering which is expected to dominate the neutrino opacity. At low momentum transfers the static structure factor is found to be small because of ion screening. In contrast, at intermediate momentum transfers the static structure factor displays a large peak due to coherent scattering from all the neutrons in a cluster. This peak moves to higher momentum transfers and decreases in amplitude as the density increases. A large static structure factor at zero momentum transfer, indicative of large density fluctuations during a first-order phase transition, may increase the neutrino opacity. However, no evidence of such an increase has been found. Therefore, it is unlikely that the system undergoes a simple first-order phase transition. Further, to compare our results to more conventional approaches, a cluster algorithm is introduced to determine the composition of the clusters in our simulations. Neutrino opacities are then calculated within a single heavy nucleus approximation as is done in most current supernova simulations. It is found that corrections to the single heavy nucleus approximation first appear at a density of the order of ${10}^{13}\phantom{\rule{0.3em}{0ex}}\mathrm{g}∕{\mathrm{cm}}^{3}$ and increase rapidly with increasing density. Thus neutrino opacities are overestimated in the single heavy nucleus approximation relative to the complete molecular dynamics simulations.
100 citations
TL;DR: In this article, the antisymmetrized molecular dynamics (AMD) approach is used to calculate nuclear collisions as dynamics of quantum many-nucleon systems, and the quantum branching into many reaction channels has been taken into account by the stochasticity of dynamics.
94 citations
TL;DR: In this article, the in-medium properties of mesons ( π, η, ρ ) and baryon resonances in cold nuclear matter within a coupled-channel analysis were studied.
93 citations
TL;DR: In this paper, the authors show that most nuclear phenomena can be reproduced by theories using either density-independent, or density-dependent masses, a grand conspiracy of nature that is an aspect that could be tied to the Cheshire Cat phenomenon in hadron physics.
TL;DR: In this article, 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_solar for reasonable values of the bag model parameters. For nuclear matter, we use the equation of state calculated by Akmal, Pandharipande, and Ravenhall using many-body techniques. Both mixed and homogeneous phases of nuclear and quark matter are considered.
TL;DR: By fixing the three parameters of the model to reproduce the binding and symmetry energy of nuclear matter, it is found that it allows a very satisfactory interpretation of the Skyrme force.
Abstract: We formulate the quark meson coupling model as a many-body effective Hamiltonian. This leads naturally to the appearance of many-body forces. We investigate the zero range limit of the model and compare its Hartree-Fock Hamiltonian to that corresponding to the Skyrme effective force. By fixing the three parameters of the model to reproduce the binding and symmetry energy of nuclear matter, we find that it allows a very satisfactory interpretation of the Skyrme force.
TL;DR: In this article, an energy functional is constructed on the basis of the microscopic bulk EoS and applied to a selection of nuclei throughout the mass table, providing a microscopic basis for a link between nuclear surface behaviour and neutron EoS previously observed with phenomenological effective forces.
TL;DR: In this paper, the spectral density of the $D$ meson in the nuclear environment is studied within a selfconsistent coupled-channel approach assuming a separable potential for the bare meson-baryon interaction.
Abstract: The spectral density of the $D$ meson in the nuclear environment is studied within a self-consistent coupled-channel approach assuming a separable potential for the bare meson-baryon interaction. The $DN$ interaction, described through a $G$ matrix, generates dynamically the ${\ensuremath{\Lambda}}_{c}(2593)$ resonance. This resonance is the charm counterpart of the $\ensuremath{\Lambda}(1405)$ resonance generated from the $s$-wave $\overline{K}N$ interaction in the $I=0$ channel. The medium modification of the $D$-meson spectral density due to the Pauli blocking of intermediate states as well as due to the dressing of the $D$ mesons, nucleons, and pions is investigated. We observe that the inclusion of coupled-channel effects and the self-consistent dressing of the $D$ meson results in an overall reduction of the in-medium $D$-meson changes compared to previous work which neglected those effects.
TL;DR: In this paper, the authors study the hadron-quark phase transition in the interior of neutron stars and find that the maximum masses are never larger than 1.6 solar masses, no matter the model chosen for describing the pure quark phase.
Abstract: We study the hadron-quark phase transition in the interior of neutron stars (NS). For the hadronic sector, we use a microscopic equation of state (EOS) involving nucleons and hyperons derived within the Brueckner-Bethe-Goldstone many-body theory, with realistic two-body and three-body forces. For the description of quark matter, we employ both the MIT bag model with a density dependent bag constant, and the color dielectric model. We calculate the structure of NS interiors with the EOS comprising both phases, and we find that the NS maximum masses are never larger than 1.6 solar masses, no matter the model chosen for describing the pure quark phase.
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.
Abstract: The roles of isospin asymmetry in nuclei and neutron stars are investigated using a range of potential and field-theoretical models of nucleonic matter. The parameters of these models are fixed by fitting the properties of homogeneous bulk matter and closed-shell nuclei. We discuss and unravel the causes of correlations among the neutron skin thickness in heavy nuclei, the pressure of beta-equilibrated matter at a density of 0.1 fm$^{-3}$, the derivative of the nuclear symmetry energy at the same density and the radii of moderate mass neutron stars. Constraints on the symmetry properties of nuclear matter from the binding energies of nuclei are examined. The extent to which forthcoming neutron skin measurements will further delimit the symmetry properties is investigated. The impact of symmetry energy constraints for the mass and moment of inertia contained within neutron star crusts and the threshold density for the nucleon direct Urca process, all of which are potentially measurable, is explored. We also comment on the minimum neutron star radius, assuming that only nucleonic matter exists within the star.
01 May 2004
TL;DR: In this paper, the effects of color superconductivity on the mass-radius relationship of compact stars have been discussed, showing that one would have to fix the bag constant by other measurements in order to see the effects.
Abstract: According to quantum chromodynamics (QCD), matter at ultra-high densities will take the form of a color-superconducting quark liquid, in which there is a condensate of Cooper pairs of quarks near the Fermi surface. I present a review of the physics of color superconductivity. I give particular attention to the recently proposed gapless CFL (gCFL) phase, which has unusual properties such as quasiquarks with a near-quadratic dispersion relation, and which may well be the favored phase of quark matter in the density range relevant to compact stars. I also discuss the effects of color superconductivity on the mass-radius relationship of compact stars, showing that one would have to fix the bag constant by other measurements in order to see the effects of color superconductivity. An additional parameter in the quark matter equation of state connected with perturbative corrections allows quark matter to imitate nuclear matter over the relevant density range so that hybrid stars can show a mass-radius relationship very similar to that of nuclear matter, and their masses can reach 1.9 M O ..
TL;DR: In this paper, the authors compare results for a representative sample of viable nuclear equations of state (EOSs) that span three qualitatively different classes of models for the description of nuclear matter.
Abstract: We construct numerical models of the newly discovered binary pulsar J0737-3039A, both with a fully relativistic, uniformly rotating equilibrium code that handles arbitrary spins and in the relativistic slow-rotation approximation. We compare results for a representative sample of viable nuclear equations of state (EOSs) that span three qualitatively different classes of models for the description of nuclear matter. A future dynamical measurement of the neutron star's moment of inertia from pulsar timing data will impose significant constraints on the nuclear EOS. Even a moderately accurate measurement ( 10%) may be able to rule out some of these competing classes. Using the measured mass, spin, and moment of inertia to identify the optimal model computed from different EOSs, one can determine the pulsar's radius.
TL;DR: In this article, the low-energy interactions of these particles are governed by chiral effective theory, and operator coefficients are determined by fitting to zero temperature few-body scattering data.
Abstract: We study nuclear and neutron matter by combining chiral effective field theory with nonperturbative lattice methods. In our approach, nucleons and pions are treated as point particles on a lattice. This allows us to probe larger volumes, lower temperatures, and greater nuclear densities than in lattice QCD. The low-energy interactions of these particles are governed by chiral effective theory, and operator coefficients are determined by fitting to zero temperature few-body scattering data. The leading dependence on the lattice spacing can be understood from the renormalization group and absorbed by renormalizing operator coefficients. In this way, we have a realistic simulation of many-body nuclear phenomena with no free parameters, a systematic expansion, and a clear theoretical connection to QCD. We present results for hot neutron matter at temperatures 20-40 MeV and densities below twice the nuclear matter density.
TL;DR: In this article, the influence of potential quark matter existing at high densities in neutron star interiors on gravitational waves (GW) emitted in a binary neutron star merger event is considered.
Abstract: We consider the influence of potential quark matter existing at high densities in neutron star interiors on gravitational waves (GW) emitted in a binary neutron star merger event. Two types of equations of state (EoS) at zero temperatures are used, one describing pure nuclear matter, the other nuclear matter with a phase transition to quark matter at very high densities. Binary equilibrium sequences close to the innermost stable circular orbit (ISCO) are calculated to determine the GW frequencies just before merger. It is found that EoS effects begin to play a role for gravitational masses larger than M∞ ≃ 1.5M⊙. The difference in the gravitational wave frequency at the ISCO grows to up to ≃ 10% for the maximal allowed mass given by the EoSs used. Then, we perform 3D hydrodynamic simulations for each EoS varying the initial mass and determine the characteristic GW frequencies of the merger remnants. The implications of quark matter show up mainly in a different collapse behaviour of the merger remnant. If the collapse does not take place immediately after merger, we find a phase difference between two EoS’s in the post-merger GW signal. We also compare the GW frequencies emitted by the merger remnant to values from simulations using a polytropic EoS and find an imprint of the non-constant adiabatic index of our EoSs. All calculations are based on the conformally flat (CF) approximation to general relativity and the GW signal from the merger simulation is extracted up to quadrupole order.
TL;DR: In this article, a point-coupling model of nuclear many-body dynamics constrained by in-medium QCD sum rules and chiral symmetry is derived, which is tested in the analysis of the equations of state for symmetric and asymmetric nuclear matter, and of bulk and single-nucleon properties of finite nuclei.
TL;DR: In this article, the stability boundary of the colloidal cluster phase is computed by invoking counter-ion condensation, and it is shown that a condensation catastrophe leading to an infinite cluster sets in if the level of charge on the colloid is too low.
Abstract: The combination of short-range attractions and long-range repulsions can lead to interesting clustering phenomena. In particular there are strong indications that the colloidal cluster phase is in fact a manifestation of such a competition. Here we compute the stability boundary of the cluster phase by invoking counter-ion condensation. It is found that a condensation catastrophe leading to an infinite cluster sets in if the level of charge on the colloid is too low. The same ingredients leading to the cluster phase are found in nuclear physics: strong short-range attractions due to nuclear force and weak long-range Coulomb repulsions. We will show explicitly here the equivalence of a semi-empirical mass formula for the binding energy of the nucleus and the free energy of a cluster in a colloidal cluster phase. This identification enables an exploitation of theoretical results from nuclear physics to the colloidal domain and, perhaps, the construction of a colloidal system mimicking various aspects of nuclear matter.
TL;DR: In this article, a self-consistent Hartree-Fock-Bogoliubov approach was used to analyze the superfluid properties of the inner crust matter of neutron stars, formed by nuclear clusters immersed in a dilute neutron gas.
Abstract: Superfluid properties of the inner crust matter of neutron stars, formed by nuclear clusters immersed in a dilute neutron gas, are analyzed in a self-consistent Hartree-Fock-Bogoliubov approach. The calculations are performed with two pairing forces, fixed so as to obtain in infinite nuclear matter the pairing gaps provided by the Gogny force or by induced interactions. It is shown that the nuclear clusters can either suppress or enhance the pairing correlations inside the inner crust matter, depending on the density of the surrounding neutrons. The profile of the pairing field in the inner crust is rather similar for both pairing forces, but the values of the pairing gaps are drastically reduced for the force which simulates the polarization effects in infinite neutron matter.
TL;DR: In this paper, the phase transition to deconfined phase is studied and the consequences in the formation of neutron stars are investigated using the quark-meson coupling model for the hadron matter and the MIT bag model for quark matter in order to build the appropriate equations of state for hybrid stars.
Abstract: The phase transition to a deconfined phase is studied and the consequences in the formation of neutron stars are investigated. We use the quark-meson coupling model for the hadron matter and the MIT bag model for the quark matter in order to build the appropriate equations of state for the hybrid stars. The properties of the stars are then calculated. The differences between unpaired and color-flavor locked quark matter are discussed.
01 Jan 2004
TL;DR: In this article, a review of finite opacity approaches (GLV, WW, WOGZ) to the computation of the induced gluon radiative energy loss and their application to the tomographic studies of the density evolution in ultrarelativistic nuclear collisions is presented.
Abstract: We review recent finite opacity approaches (GLV, WW, WOGZ) to the computation of the induced gluon radiative energy loss and their application to the tomographic studies of the density evolution in ultra-relativistic nuclear collisions.
01 Jan 2004
TL;DR: Next Generation Relativistic Models: Covariant effective field theory for nuclear Structure and Nuclear Currents as discussed by the authors explores the Nucleus in the context of low-energy QCD.
Abstract: Next Generation Relativistic Models- Covariant Effective Field Theory for Nuclear Structure and Nuclear Currents- Exploring The Nucleus in the Context of Low-Energy QCD- The Relativistic Dirac-Brueckner Approach to Nuclear Matter- Density Dependent Relativistic Field Theory - Covariant Density Functional Theory and Applications to Finite Nuclei- Symmetry in the Relativistic Mean Field Approximation- Vacuum, Matter, and Antimatter- Mean Field: Relativistic Versus Non-Relativistic- Angular Momentum Projection and Quadrupole Correlations Effects in Atomic Nuclei- Pairing and Continuum Effects in Exotic Nuclei
TL;DR: In this paper, the effect of the baryon Dirac sea on the in-medium hadronic properties is investigated using a chiral SU(3) model in the nonlinear realization.
Abstract: The effect of vacuum fluctuations on the in-medium hadronic properties is investigated using a chiral SU(3) model in the nonlinear realization. The effect of the baryon Dirac sea is seen to modify hadronic properties and in contrast to a calculation in mean-field approximation it is seen to give rise to a significant drop of the vector meson masses in hot and dense matter. This effect is taken into account through the summation of baryonic tadpole diagrams in the relativistic Hartree approximation, where the baryon self-energy is modified due to interactions with both the nonstrange $(\ensuremath{\sigma})$ and the strange $(\ensuremath{\zeta})$ scalar fields.