Showing papers on "Nuclear matter published in 1991"
TL;DR: In this paper, an equation of state for hot, dense matter is presented in a form that is sufficiently rapid to use directly in hydrodynamical simulations, for example, in stellar collapse calculations.
1,188 citations
TL;DR: In this article, a detailed derivation of the quantum molecular dynamics equation, discussed the various approximations necessary to derive this equation and to make actual calculations feasible, is presented, and the calculations presented aim at the solution of two of the most interesting questions of contemporary heavy ion physics: What causes a nucleus to fragment into many heavy pieces, and can we determine the nuclear equation of state from heavy ion reactions?
930 citations
TL;DR: It is shown that the direct URCA process can occur in neutron stars if the proton concentration exceeds some critical value in the range 11--15%.
Abstract: We show that the direct URCA process can occur in neutron stars if the proton concentration exceeds some critical value in the range 11--15%. The proton concentration, which is determined by the poorly known symmetry energy of matter above nuclear density, exceeds the critical value in many current calculations. If it occurs, the direct URCA process enhances neutrino emission and neutron star cooling rates by a large factor compared to any process considered previously.
645 citations
TL;DR: In this paper, a new parametrization of the nucleon-nucleus optical-model potential based on data for A = 40 to 209, protons energies of 16 to 65 MeV and neutron energies of 10 to 26 MeV, including extensive polarized-beam data.
351 citations
TL;DR: The present calculations of the incompressibility predict a strong softening of the equation of state going from symmetric to asymmetric nuclear matter.
Abstract: Systematic calculations of asymmetric nuclear matter have been performed in the framework of the Brueckner-Bethe-Goldstone approach in a wide range of both density and asymmetry parameter. The empirical parabolic law fulfilled by the binding energy per nucleon is confirmed by the present results in all the range of the asymmetry parameter values. The predominant role of the $^{3}$${\mathit{S}}_{1\mathrm{\ensuremath{-}}}^{3}$${\mathit{D}}_{1}$ component of the NN interaction is elucidated. A linear variation of the proton and neutron single-particle potentials is found as increasing the neutron excess; a deviation from the phenomenological potentials occurs for highly asymmetric matter as an effect of the self-consistency. The present calculations of the incompressibility predict a strong softening of the equation of state going from symmetric to asymmetric nuclear matter. The proton fraction in equilibrium with neutron matter has been determined from the beta-stability condition and its relevance to the superfluidity of neutron stars has been investigated.
296 citations
TL;DR: Coupled cluster (CC) techniques have been developed to calculate excited states, energies of open-shell systems, density matrices and hence other properties, sum rules, and sub-sum-rules that follow from imbedding linear response theory within the NCCM.
Abstract: What has since become known as the normal coupled cluster method (NCCM) was invented about thirty years ago to calculate ground-state energies of closed-shell atomic nuclei. Coupled cluster (CC) techniques have since been developed to calculate excited states, energies of open-shell systems, density matrices and hence other properties, sum rules, and the sub-sum-rules that follow from imbedding linear response theory within the NCCM. Further extensions deal both with systems at nonzero temperature and with general dynamical behaviour. More recently, a new version of CC theory, the so-called extended coupled cluster method (ECCM) has been introduced. It has the potential to describe such global phenomena as phase transitions, spontaneous symmetry breaking, states of topological excitation, and nonequilibrium behaviour. CC techniques are now widely recognized as providing one of the most universally applicable, most powerful, and most accurate of all microscopicab initio methods in quantum many-body theory. The number of successful applications within physics is now impressively large. In most such cases the numerical results are either the best or among the best available. A typical case is the electron gas, where the CC results for the correlation energy agree over the entire metallic density range to within less than 1 millihartree (or <1%) with the essentially exact Green's function Monte Carlo results. The role of CC theory within modern quantum many-body theory is first surveyed, by a comparison with other techniques. Its full range of applications in physics is then reviewed. These include problems in nuclear physics, both for finite nuclei and infinite nuclear matter; the electron gas; various integrable and nonintegrable models; various relativistic quantum field theories; and quantum spin chain and lattice models. Particular applications of the ECCM include the quantum hydrodynamics of a zero-temperature, strongly-interacting condensed Bose fluid; a charged impurity in a polarizable medium (e.g., positron annihilation in metals); and various anharmonic oscillator and spin systems.
268 citations
TL;DR: The thermodynamically consistent procedure to introduce the excluded volume effect into the equation of state of nuclear matter has been presented in this article, in the framework of a mean-field model for hadrons with eigenvolume.
Abstract: We present the thermodynamically consistent procedure to introduce the excluded volume effect into the equation of state of nuclear matter. Implications are discussed in the framework of a mean-field model for hadrons with eigenvolume.
256 citations
TL;DR: In this paper, a relativistic theory of pairing correlations in nuclei is presented based on an extended mean field approximation, which contains apart from the kinetic term of Dirac and the self-consistent mesonic fields, known from relativist mean field theory, a Fock term and a pairing potential.
Abstract: Starting from a Lagrangian with nucleonic and mesonic degrees of freedom, a relativistic theory of pairing correlations in nuclei is presented. Based on an extended mean field approximationDirac-Hartree-Fock-Bogoliubov equations are derived, which contain apart from the kinetic term of Dirac and the self-consistent mesonic fields, known from relativistic mean field theory, a Fock term and a pairing potential. This theory is applied to a relativistic description of pairing correlations in symmetric nuclear matter. Several phenomenological models are investigated.
156 citations
TL;DR: In this paper, the authors considered mostly nuclear matter, and in particular the equation of state (EOS) at T = 0.6 independent of the VSI, and consistent with that obtained from the spin-orbit splitting.
119 citations
TL;DR: In this paper, an attempt was made to obtain the main properties of nuclear matter by QCD sum rules technique, which does not use the concept of N - N interaction. But this approach did not use any free parameters in the model, and the expectation values of certain quark and gluon field operators averaged over vacuum were involved.
115 citations
TL;DR: Nucleon self-energies in nuclear matter are studied by analyzing the correlator of nucleon interpolating fields using QCD sum-rule methods, and are comparable to the optical potentials of Dirac phenomenology.
Abstract: Nucleon self-energies in nuclear matter are studied by analyzing the correlator of nucleon interpolating fields using QCD sum-rule methods. Large Lorentz scalar and vector self-energies arise naturally, and are comparable to the optical potentials of Dirac phenomenology. The key phenomenological inputs are the baryon density and the value of the nucleon {sigma} term.
TL;DR: In the hydrochemical model for heavy-ion collisions, it is demonstrated that the observed enhancement of kaon yield in high-energy heavy-ions collisions can be explained if the medium effect is included.
Abstract: In heavy-ion collisions, kaons can be produced from baryon-baryon, meson-baryon, and meson-meson interactions. Simple meson-exchange models are introduced to study kaon production from these processes in the free space. These models are then extended to determine kaon production in hot, dense nuclear matter by taking into account the decreasing hadron masses as a result of the restoration of chiral symmetry and the condensation of kaons. We find that the cross sections for kaon production from all three processes are enhanced. In particular, the effect of decreasing hadron masses on kaon production from the meson-meson annihilation is most significant. In the hydrochemical model for heavy-ion collisions, we demonstrate that the observed enhancement of kaon yield in high-energy heavy-ion collisions can be explained if the medium effect is included.
TL;DR: It is shown that, unlike what is commonly stated, the nucleon momentum distribution is not simply defined in terms of the deriva- tive of the asymptotic scaling function, but as a sum of such a derivative plus the derivative of a quantity, the binding correction, generated by the removal energy distribution of nucleons embed- ded in the nuclear medium.
Abstract: The approach to y scaling previously adopted to obtain the nucleon momentum distribution in the two- and three-nucleon systems is extended to the case of complex nuclei and nuclear matter. The basic elements of this approach, which takes properly into account nucleon binding and momentum, are reviewed. A new method of analysis, which allows one to obtain the experimental asymptotic scaling function from inclusive cross sections even if these data are affected by final-state interactions, is proposed and illustrated. By such a method, the asymptotic scaling functions of $^{3}\mathrm{He}$, $^{4}\mathrm{He}$, $^{12}\mathrm{C}$, $^{56}\mathrm{Fe}$, and nuclear matter are obtained from recent experimental data and it is demonstrated that, particularly at high negative values of the scaling variable, the available data points at the highest value of the momentum transfer are affected by final-state interaction and cannot therefore be considered to represent the asymptotic scaling function. It is shown that, unlike what is commonly stated, the nucleon momentum distribution is not simply defined in terms of the derivative of the asymptotic scaling function, but as a sum of such a derivative plus the derivative of a quantity, the binding correction, generated by the removal energy distribution of nucleons embedded in the nuclear medium.The binding correction and its derivative are evaluated with various types of spectral functions, and the nucleon momentum distributions in $^{3}\mathrm{He}$, $^{4}\mathrm{He}$, $^{12}\mathrm{C}$, $^{56}\mathrm{Fe}$, and nuclear matter are obtained up to nucleon momenta k\ensuremath{\approxeq}500 MeV/c. For few-body systems the obtained momentum distributions satisfactorily agree with the ones extracted from (e,e'p) reactions and with theoretical calculations performed within Faddeev or variational approaches, whereas for complex nuclei they qualitatively agree with predictions of theoretical many-body approaches which take nucleon-nucleon correlations into account and, at the same time, at k\ensuremath{\ge}350 MeV/c they are larger by orders of magnitude than the ones predicted by mean field approaches. Such a result does represent unambiguous evidence of correlation effects in nuclei.
CERN1
TL;DR: In this article, the authors show that uncertainties in the strength of interactions of hyperons among themselves and with nucleons lead to a large uncertainty in the maximum allowed neutron star mass, even if the properties of nuclear and neutron matter are known with infinite precision around normal nuclear matter density and below.
TL;DR: Using the leading operators in the chiral lagrangian for meson-baryon interactions (at low momentum) and treating the meson fields classically, Kaplan and Nelson have observed, using numerical methods, that a charged kaon condensate forms at several times nuclear density.
TL;DR: The cross section for inclusive electron scattering by nuclear matter is calculated at high momentum transfers using a microscopic spectral function, and compared with that extrapolated from data on laboratory nuclei, found that the cross section obtained with the plane-wave impulse approximation is close to the observed data at large values of the energy loss, but too small at low values.
Abstract: The cross section for inclusive electron scattering by nuclear matter is calculated at high momentum transfers using a microscopic spectral function, and compared with that extrapolated from data on laboratory nuclei. It is found that the cross section obtained with the plane-wave impulse approximation is close to the observed data at large values of the energy loss, but too small at low values. In this regime final-state interactions are important; after including their effects theory and data are in fair agreement. It is necessary to treat nucleon-nucleon correlations consistently in estimating the final-state interactions. The effects of possible time dependence of the nucleon-nucleon cross section, giving rise to nuclear transparency, are also investigated. The y scaling of the response function is discussed to further elucidate the role of final-state interactions.
TL;DR: In this paper, a full spectral analysis for the production of c-bar c and b-bar b resonances is presented, which can be used to explore the primordial state of matter produced in high energy heavy ion collisions.
Abstract: The intensity of spectral lines in the light emitted by stars gives information about the thermodynamic state of stellar matter. Similarly, the intensity of charmonium and bottonium lines in the spectrum of dileptons emitted in nuclear collisions can provide information about the early thermodynamic state of any strongly interacting matter created in such collisions. TheJ/ϕ suppression found in centralO-U andS-U collisions is a first instance of a change in spectral intensity. We develop a full spectral analysis for the production of\(c\bar c\) and\(b\bar b\) resonances and discuss how it can be used to explore the primordial state of matter produced in high energy heavy ion collisions.
01 Jan 1991
TL;DR: In this paper, the authors calculated the cross section for inclusive electron scattering by nuclear matter at high momentum transfers using a microscopic spectral function, and compared with that extrapolated from data on laboratory nuclei.
Abstract: The cross section for inclusive electron scattering by nuclear matter is calculated at high momentum transfers using a microscopic spectral function, and compared with that extrapolated from data on laboratory nuclei. It is found that the cross section obtained with the plane-wave impulse approximation is close to the observed data at large values of the energy loss, but too small at low values. In this regime final-state interactions are important; after including their effects theory and data are in fair agreement. It is necessary to treat nucleon-nucleon correlations consistently in estimating the final-state interactions. The effects of possible time dependence of the nucleon-nucleon cross section, giving rise to nuclear transparency, are also investigated. The {ital y} scaling of the response function is discussed to further elucidate the role of final-state interactions.
TL;DR: Starting from a relativistic Lagrangian, a conserving approximation for the description of nuclear matter is derived and it is shown to be a nontrivial extension over the relativist Dirac-Brueckner scheme.
Abstract: Starting from a relativistic Lagrangian we derive a conserving'' approximation for the description of nuclear matter. We show this to be a nontrivial extension over the relativistic Dirac-Brueckner scheme. The saturation point of the equation of state calculated agrees very well with the empirical saturation point. The conserving character of the approach is tested by means of the Hugenholtz--van Hove theorem. We find the theorem fulfilled very well around saturation. A new value for compression modulus is derived, {ital K}=310 MeV. Also we calculate the occupation probabilities at normal nuclear matter densities by means of the spectral function. The average depletion {kappa} of the Fermi sea is found to be {kappa}{similar to}0.11.
TL;DR: Modeling fluctuations by a distribution of cross sections, their effect on multiplicity and transverse energy production in central high-energy nuclear collisions is calculated and it is found that they can account for the large fluctuations found experimentally.
Abstract: Fluctuations in the wave functions of hadrons in inelastic interactions with nuclei are important for nuclear collisions at high energy, where the internal hadronic configurations can be considered frozen. Modeling fluctuations by a distribution of cross sections, we calculate their effect on multiplicity and transverse energy production in central high-energy nuclear collisions, and find that they can account for the large fluctuations found experimentally.
TL;DR: In this article, an extended Skyrme-Landau interaction (SL1) with velocity-dependent three-body forces and a tensor force is developed. But the interaction parameters are determined by the better known Landau-Migdal parameters in nuclear matter and other physical quantities like the surface energy and the dipole sum rule.
TL;DR: In this paper, a quasi-classical many-body model was used to simulate nuclear matter at finite temperatures and it was shown that considerable clustering develops at subsaturation densities.
TL;DR: In this paper, it was shown that the pion mass can change much more rapidly with density than with temperature, at least for moderate changes in each, and that the decreasing pion masses, while not effective in pion nuclear processes at zero temperature, should play an important role in heavy-ion collisions.
TL;DR: In this article, a survey of simple pairing properties for the Reid potential is made and it is suggested that the actual ground state of nuclear matter around the empirical saturation density corresponds to a superfluid with pairing occurring with deuteron quantum numbers.
TL;DR: In this paper, the neutrino scattering from a dense degenerate gas of electrons, protons and neutrons is investigated, where correlations induced by the Coulomb interactions of the electrons and protons are considered.
TL;DR: A model spectral function expressed through a convolution integral of the momentum distributions describing the relative and center-of-mass motion of a correlated pair is suggested and shown to satisfactorily reproduce the spectral function of the three-body system and nuclear matter calculated in terms of realistic nucleon-nucleon interactions in a wide range of nucleon momenta and removal energies.
Abstract: The basic two-nucleon configurations which generate the structure of the nucleon spectral function at high values of momenta and removal energies are analyzed. A model spectral function expressed through a convolution integral of the momentum distributions describing the relative and center-of-mass motion of a correlated pair is suggested and shown to satisfactorily reproduce the spectral function of the three-body system and nuclear matter calculated in terms of realistic nucleon-nucleon interactions in a wide range of nucleon momenta and removal energies.
TL;DR: The saturation curve of symmetric nuclear matter is calculated at the Brueckner-Hartree-Fock level of approximation within the continuous choice for the single-particle potential and the binding energies per nucleon around saturation agree closely with previous results obtained with separable versions of the same potential.
Abstract: The saturation curve of symmetric nuclear matter is calculated at the Brueckner-Hartree-Fock level of approximation within the continuous choice for the single-particle potential. The realistic local Argonne ${\mathit{v}}_{14}$ potential is used and the results are compared with similar calculations presented in the literature. The binding energies per nucleon around saturation agree closely with previous results obtained with separable versions of the same potential as well as of the Paris potential.
TL;DR: Coulomb instability in hot nuclei is discussed, using the Skyrme effective nucleon-nucleon interactions and a mean-field approach based on a finite-temperature real-time Green's-function method.
Abstract: Coulomb instability in hot nuclei is discussed, using the Skyrme effective nucleon-nucleon interactions and a mean-field approach based on a finite-temperature real-time Green's-function method. In the calculation, full degeneracy and symmetry corrections are included. It is found that the above precise treatment of degeneracy and symmetry corrections is necessary in the lower-temperature and higher-density region or for larger asymmetry. The calculated limiting temperatures are quite different for different sets of Skyrme effective interactions, which may be used as a sensitive test of the various Skyrme interactions to see which one can best describe the finite-temperature properties of nuclear matter. It is also found that the limiting temperature ${\mathit{T}}_{\mathrm{lim}}$ is approximately proportional to the critical temperature ${\mathit{T}}_{\mathit{C}}$, when the results for various Skyrme interactions are compared.
TL;DR: A Comment on the Letter by S. J. Brodsky is posted on the website of the American Physical Society.
Abstract: A Comment on the Letter by S J Brodsky {ital et} {ital al}, Phys Rev Lett 64, 1011 (1990)
TL;DR: The role of the rho-meson field, which provides the isovector interaction among nucleons, in determining nuclear properties far from the stability line was studied in this paper.