Landau-Ginzburg treatment of nuclear matter at finite temperature

Based on recent studies of the temperature dependence of the energy and specific heat of liquid nuclear matter, a phase transition is suggested at a temperature ∼ 0.85 MeV. We apply the Landau-Ginzburg theory to this transition and determine the behaviour of the energy and specific heat close to the critical temperature in the condensed phase. Received: 29 July 2000 / Accepted: 20 October 2000     

Lattice density waves in nuclear matter at finite temperature

Symmetric nuclear matter at finite temperature is studied, within the Thermal Hartree Fock framework, employing lattice density waves and density dependent forces of the Skyrme type. The disappearance of clusters at finite temperature is described and its characteristics are quantiatively determined.     

The properties of nuclear matter at zero and finite temperatures

The properties of nuclear matter are studied in the frame of the Brueckner theory. The Brueckner-Hartree-Fock approximation plus two-body density-dependent Skyrme potential which is equivalent to three-body interaction are used. Various modern nucleon-nucleon potentials are used in the framework of the Brueckner-Hartree-Fock approximation, e.g.: CD-Bonn potential, Nijm1 potential, and Reid 93 potential. These modern nucleon-nucleon potentials fit the deuteron properties and are phase shifts equivalent. The equation of state at T = 0, pressure at T = 0, 8, and 12 MeV, free energy at T = 8 and 12 MeV, nuclear matter incompressibility, and the symmetry energy calculation are presented. The hot properties of nuclear matter are calculated using T ²-approximation method at low temperatures. Good agreement is obtained in comparison with previous theoretical estimates and experimental data, especially at low densities.     

Light clusters in nuclear matter of finite temperature

We investigate properties and the distribution of light nuclei ( ) in symmetric nuclear matter of finite temperature within a microscopic framework. For this purpose we have solved few-body Alt-Grassberger-Sandhas-type equations for quasi-nucleons that include self-energy corrections and Pauli blocking in a systematic way. In a statistical model we find a significant influence in the composition of nuclear matter if medium effects are included in the microscopic calculation of nuclei. If multiplicities are frozen out at a certain time (or volume), we expect significant consequences for the formation of light fragments in a heavy ion collision. As a consequence of the systematic inclusion of medium effects, the ordering of multiplicities becomes opposite to the law-of-mass action of ideal components. This is necessary to explain the large abundance of -particles in a heavy ion collision that are otherwise largely suppressed in an ideal equilibrium scenario.PACS: 25.70.-z Low and intermediate energy heavy-ion reactions - 25.70.Pq Multifragment emission and correlations - 21.65. + f Nuclear matter - 21.45. + v Few-body systems     

Pairing correlations in finite nuclear systems

We discuss an approach for the treatment of correlations in finite nuclear systems. The approach is based on a boson formalism, the basic boson operators representing elementary particle-hole excitations. We show an application of the method within an exactly solvable multilevel pairing model. We calculate the correlation energy of the system and compare it with the exact results as well as with results obtained within other approaches.     

Damping of nuclear excitations at finite temperature

We calculate the damping of single-particle motion and of vibrational motion to lowest order in the coupling between the particles and the vibrations, using the finite temperature Matsubara formalism. The derived formulas have a complicated structure which however can be mostly understood in physical terms. We apply the theory to single-particle states in heavy nuclei, to the giant dipole vibration in ⁹⁰Zr, and to the giant quadrupole vibration in ²⁰⁸Pb. Even at temperatures of the order of 3 MeV the main peak of the giant vibrations remains essentially unaffected although it acquires a long tail at the low-energy end.     

Relativistic nuclear and neutron matter at finite temperatures

Nuclear matter as well as neutron matter is studied in the framework of a relativistic nuclear field theory at finite temperature. A spectral representation for the two-point Green's function at finite temperature and finite density is constructed. The bulk properties of the interacting system are calculated in the Hartree and Hartree-Fock approach. In additionσ ³- andσ ⁴-self-interactions have been taken into account. We present and discuss the results of hot and dense matter for temperaturesT≦ 50 MeV and densitiesθ≦6θ ₀ (ρ ₀≈0.17 fm^?3) using six different model parameter sets.     

Pairing effects at finite temperature and finite rotational frequencies: An exactly soluble model

We propose a new type of experiment to look for parity violation due to neutral current interactions in deuterium. This involves measuring a certain angular momentum transfer from an atomic beam of polarized 2S _1/2 deuterium to a capacitor producing a constant electric field. The torque exerted on the capacitor which is to be measured turns out to be of order 10⁷ ?/s in a realistic situation.     

Thermophysical properties of iridium at finite temperature

The bulk properties of materials in an extreme environment such as high temperature and high pressure can be understood by studying anharmonic effects due to the vibration of lattice ions and thermally excited electrons.In this spirit,in the present paper,anharmonic effects are studied by using the recently proposed mean-field potential(MFP) approach and Mermin functional which arise due to the vibration of lattice ions and thermally excited electrons,respectively.The MFP experienced by a wanderer atom in the presence of surrounding atoms is constructed in terms of cold energy using the local form of the pseudopotential.We have calculated the temperature variation of several thermophysical properties in an extreme environment up to melting temperature.The results of our calculations are in excellent agreement with the experimental findings as well as the theoretical results obtained by using first principle methods.We conclude that presently used conjunction scheme(MFP+pseudo potential) is simple computationally,transparent physically,and accurate in the sense that the results generated are comparable and sometimes better than the results obtained by first principle methods.Local pseudopotential used is transferable to extreme environment without adjusting its parameters.     

Microscopic calculations of spin polarized neutron matter at finite temperature

The properties of spin polarized neutron matter are studied both at zero and finite temperature within the framework of the Brueckner–Hartree–Fock formalism, using the Argonne v18 nucleon–nucleon interaction. The free energy, energy and entropy per particle are calculated for several values of the spin polarization, densities and temperatures together with the magnetic susceptibility of the system. The results show no indication of a ferromagnetic transition at any density and temperature.     

Equation of state for pion-condensed neutron matter at finite temperature

The equation of state for neutron matter in the presence of a pion condensate is investigated at finite, but small temperature within the σ model. It is found that a transition of van der Waals type takes place at low temperature for sufficiently strong effective p-wave interaction, which disappears however beyond a critical temperature T_c. Within a wide variety of model assumptions, an upper limit of about 50 MeV is found for T_c.     

The collision integral in nuclear matter at zero temperature

The collision rate in an infinite Fermi system having a deformed Fermi surface is computed in the limit of small deformation. For a given amount of internal energy, the damping rate is nearly independent of temperature. The calculation is applied to thermalization in heavy ion collisions. We find that the collisional damping time is comparable to the duration of the collision for medium-weight nuclei. Thus the predictions of mean field theory, such as the presence of a fusion window at small impact parameters, will only have validity for lighter ions.     

Isotope shifts in finite nuclei and the pairing properties of nuclear matter

A uniform nuclear matter with s-wave pairing is studied within the local energy-density functional approach, incorporating a few parameter sets extracted from the analysis of isotope shifts in finite nuclei. The dilute limit, in which the regime changes from weak to strong pairing, is considered in detail, and, for strong coupling, the ground state properties of that system are found to be completely determined in leading order by the singlet scattering length a _nn . The combination of a density-dependent contact pairing interaction and an energy cutoff adjusted to produce a realistic value of a _nn is shown to be the preferred choice among the deduced parameter sets. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 4, 235–241 (25 August 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Particle clustering and Mott transitions in nuclear matter at finite temperature: (I). Method and general aspects

The thermodynamic state of nuclear matter as regards dependence on density and temperature is considered. Expressions for the association degree are derived describing the ratio of nuclear matter which is clustered to bound states. The problem of two nucleons imbedded in the surrounding nuclear matter is considered with the help of the Bethe-Goldstone equation for thermodynamic Green functions. The two-particle energy shift due to the effective nuclear matter hamiltonian is considered in a Hartree-Fock approximation, and a Mott density is obtained so that for densities of nuclear matter higher than the Mott density bound states cannot exist. With a simplified effective two-nucleon interaction the association degree is calculated as a function of the nucleon density and the temperature.     

有限温度下一维Gaudin-Yang模型的热力学性质

本文通过数值求解有限温度下一维均匀费米Gaudin-Yang模型的热力学Bethe-ansatz方程, 研究了此模型的基本性质,得到了在给定的温度或给定的相互作用下, 化学势、相互作用、粒子密度和熵的相互变化图像. 对结果分析发现, 在给定温度和相互作用下, 熵随着化学势的变化有一个量子临界区域.     

Instabilities in nuclear matter and finite nuclei

Spinodal instability in nuclear matter and finite nuclei is investigated. This instability occurs in the low-density region of the phase diagram. The thermodynamical and dynamical analysis is based on Landau theory of Fermi liquids. It is shown that asymmetric nuclear matter can be characterized by a unique spinodal region, defined by the instability against isoscalar-like fluctuation, as in symmetric nuclear matter. Everywhere in this density region the system is stable against isovector-like fluctuations related to the species separation tendency. Nevertheless, this instability in asymmetric nuclear matter induces isospin distillation leading to a more symmetric liquid phase and a more neutron-rich gas phase.     

Quark matter and meson properties in a Nonlocal SU(3) chiral quark model at finite temperature

We study the finite temperature behavior of light scalar and pseudoscalar meson properties in the context of a three-flavor nonlocal chiral quark model. The model includes mixing with active strangeness degrees of freedom, and takes care of the effect of gauge interactions by coupling the quarks with a background color field. We analyze the chiral restoration and deconfinement transitions, as well as the temperature dependence of meson masses, mixing angles, and decay constants.