Saturation of nuclear matter and short-range correlations

A fully self-consistent treatment of short-range correlations in nuclear matter is presented. Different implementations of the determination of the nucleon spectral functions for different interactions are shown to be consistent with each other. The resulting saturation densities are closer to the empirical result when compared with (continuous choice) Brueckner-Hartree-Fock values. Arguments for the dominance of short-range correlations in determining the nuclear matter saturation density are presented. A further survey of the role of long-range correlations suggests that the inclusion of pionic contributions to ring diagrams in nuclear matter leads to higher saturation densities than empirically observed. A possible resolution of the nuclear matter saturation problem is suggested.     

The unitary-model-approach for tensor correlations in nuclear matter

The unitary-model-approach for nuclear matter is extended to the treatment of tensor forces. Suitable spin-dependent correlations are employed. The method is demonstrated at hand of the deuteron problem. For nuclear matter calculations and numerical results for the phenomenological soft-core potential of Eikemeier and Hackenbroich are presented. The increase of binding energy by the inclusion of unitary tensor correlations amounts up to 5 MeV per particle.     

Longitudinal spin-dependent correlations in nuclear matter

A Jastrow-type wave function, with the two-body correlation factor depending on the spin-isospin state of the particles, is used for variational calculations of the energy per particle of infinite Fermi systems. Results are presented for nuclear matter and neutron matter using two semi-realistic potentials.     

The role of the form factor and short-range correlation in the relativistic Hartree-Fock model for nuclear matter

The role of the form factor and short-range correlation in nuclear matter is studied within the relativistic Hartree-Fock approximation. We take, first, the mean-field approximation for meson fields and obtain the fluctuation terms of mesons to be used for the Fock energies. We introduce form factors in the meson-nucleon coupling vertices to take into account the finite-size effect of the nucleon. We use further the unitary correlation operator method for the treatment of the short-range correlation. The form factors of the size ( L \Lambda ∼ 1.0 -2.0GeV) of the nucleon-nucleon interaction cut down largely the contribution of the r \rho -meson in the Fock term. The short-range correlation effect is not large but has a significant effect on the pion and r \rho -meson energies in the relativistic Hartree-Fock approximation for nuclear matter.     

A simple semiempirical equation of state for cold nuclear matter

On the basis of gross properties of nuclei, a simple semiempirical equation of state is developed for cold hadronic matter composed of light quarks of two flavors. The source of binding energy in the model is the decreasing asymmetry between the number of up and down quarks in extended regions of overlapping nucleons. The resulting incompressibility of symmetric nuclear matter at equilibrium density is K=324 MeV. The incompressibility decreases rapidly with decreasing density but increases only slowly with increasing density until homogenous quark matter is reached at a density just above three times ordinary nuclear matter density.     

Alpha-particle model for nuclear matter

Infinite nuclear matter is assumed to be composed of an equal even number of protons and neutrons. The surface region of nuclear matter is replaced by an assembly of alpha-particles interacting through a potential composed of a strong short-range repulsion and a weak long-range attraction of the Gaussian form. The energy gap in nuclear matter and the effective mass of alpha particles have been calculated. The result shows that the energy gap is more than 2 MeV but 5 MeV. The ratio of the effective mass m* to the free particle mass m of alpha-particles is always greater than unity and its maximum value is a little over 5. For an assembly of alpha-particles to be stable, it must be a dilute weakly interacting assembly. The net interaction must be repulsive and the nuclear density should be less than the saturation limit. The results have been compared with previous calculations.The author is very grateful to Prof. B. R. Seth, Prof. A. M. Sessler and Prof. S. Duttamazumdar for encouragement and helpful discussions.     

A simple model for the nuclear curvature energy

Using the well-known analytically soluble model of semi-infinite nuclear matter of Wilets, we deduce a closed expression for the nuclear curvature energy as a function of the surface profile asymmetry; the values obtained for the curvature coefficient are in good agreement with those extracted from realistic calculations. A generalization of this procedure could be a way out of the difficulties arising in Hartree-Fock calculations of the curvature coefficient.     

Momentum distributions for model nuclear matter

The occupation probability for single-particle orbitals corresponding to a state-independent Jastrow-Slater wavefunction is evaluated for two semi-realistic models of nuclear matter within the framework of Fermi hypernetted-chain theory.     

Single-particle potential in a chiral approach to nuclear matter including short-range NN-terms

We extend a recent chiral approach to nuclear matter of Lutz et al.Phys. Lett. B 474, 7 (2000)) by calculating the underlying (complex-valued) single-particle potential U(p, k _f) + iW(p, k _f). The potential for a nucleon at the bottom of the Fermi sea, U(0, k _f0) = - 20.0 MeV, comes out as much too weakly attractive in this approach. Even more seriously, the total single-particle energy does not rise monotonically with the nucleon momentum p, implying a negative effective nucleon mass at the Fermi surface. Also, the imaginary single-particle potential, W(0, k _f0) = 51.1 MeV, is too large. More realistic single-particle properties together with a good nuclear-matter equation of state can be obtained if the short-range contributions of non-pionic origin are treated in mean-field approximation (i.e. if they are not further iterated with 1π-exchange). We also consider the equation of state of pure neutron matter ˉE_n(k _n) and the asymmetry energy A(k _f) in that approach. The downward bending of these quantities above nuclear-matter saturation density seems to be a generic feature of perturbative chiral pion-nucleon dynamics. Received: 19 December 2002 / Accepted: 11 February 2003 / Published online: 15 April 2003     

Soft-core correlations and three body forces in nuclear matter

We show that, when nucleon-nucleon correlations are taken into account using correlation functions derived. from the Reid soft core potential, the contribution of three body forces to the binding energy of nuclear matter is enhanced. The two pion exchange three body forces contributes 6 MeV attraction.     

Pseudorapidity dependence of short-range correlations from a multi-phase transport model

Using a multi-phase transport model(AMPT) that includes both initial partonic and hadronic interactions, we study neighboring bin multiplicity correlations as a function of pseudorapidity in Au+Au collisions at (sNN)~(1/2) = 7.7- 62.4 GeV.It is observed that for (sNN)~(1/2) 19.6 GeV Au+Au collisions, the short-range correlations of final particles have a trough at central pseudorapidity, while for (sNN)~(1/2) 19.6 GeV AuAu collisions,the short-range correlations of final particles have a peak at central pseudorapidity. Our findings indicate that the pseudorapidity dependence of short-range correlations should contain some new physical information, and are not a simple result of the pseudorapidity distribution of final particles. The AMPT results with and without hadronic scattering are compared. It is found that hadron scattering can only increase the short-range correlations to some level, but is not responsible for the different correlation shapes for different energies. Further study shows that the different pseudorapidity dependence of short-range correlations are mainly due to partonic evolution and the following hadronization scheme.     

A sigma-omega-quark model to saturate nuclear matter

A sigma-omega-quark model is investigated to explain the saturation properties of nuclear matter. The quark structure of the nucleon induces a mechanism for saturation by weakening the attraction due to the sigma meson at high density. The boost of the composite system and some center-of-mass corrections are new sources of repulsion and therefore strongly reduce the need for an omega meson.     

A simple model for nuclear forces which exhibits bound states

A repulsive core force is derived which, assuming mesons are the field particles, gives binding energies in good agreement with binding energies per nucleon of heavy nuclei. The physical model consists of a field of relatively short range, in which emission of a meson by a nucleon and subsequent absorption by a neighboring nucleon is equivalent to a potential well. The binding energy at the equilibrium spacing of the nucleons is the self-energy of the mesons, which is calculated by analogy with classical electric fields.     

A simple model calculation of pion condensation in neutron matter

The charged pion condensed state in pure neutron matter is described analytically in an approximate calculation based on the chirally invariant σ-model. The calculation includes s- and p-wave condensed pion-nucleon interactions, pi-pi interactions, the effect of the N¹ (1236) resonance, and the (Ericson-Ericson Lorentz-Lorentz) effect of nuclear correlations.     

A simple relation between bulk and surface properties of nuclear matter

Starting from a previously derived relation between the derivatives of the bulk nucleon energy e(n_c) and the surface tension σ(n_c) with respect to the central density n_c we obtain a simple model-independent relation between the values of n_c, σ(n_c), the surface parameter t and the bulk modulus K_∞ at saturation. This relation is checked for values obtained in ETF calculations. K_∞=230 MeV is calculated from the well-known experimental values of n₀, σ₀ and t₀.     

A simplified approach to three-body correlations in nuclear matter through a non-zero particle spectrum

Self-consistent nuclear-matter calculations are presented which take into account Dahlblom's results for the contribution to the binding energy due to three-body correlations. We propose a justified parametrization of the single-particle potential for particle states, the energy contribution of which cancels approximately the energy from certain three-body correlations. Indications are given of how to fix this particle-state potential for a given two-body interaction. Two nucleon-nucleon potentials are used: the Reid soft-core potential and a fully momentum-dependent one-boson-exchange potential similar to the form proposed by Ingber and Potenza. The mechanism of the increase in the total wound due to three-body correlations is investigated and reasons are given why this does not prevent the saturation densities from moving to higher values. Due to three-body correlations and with self-consistency on the hole spectrum, the increase in nuclear-matter binding energy is 0.60 MeV/A for the Reid soft-core interaction and 0.68 Mev/A for the OBEP. The saturation momentum is shifted from 1.42 fm^?1 to 1.44 fm^?1 for the Reid potential and from 1.58 fm^?1 to 1.62 fm^?1 for the OBEP.     

Long-range spatial correlations in a simple diffusion model

A simple anisotropic diffusion model, according to semiphenomenological arguments, exhibits long-ranged spatial correlations in uniform stationary states.