Finite temperature effects in antiferromagnetism of nuclear matter

The influence of the finite temperature on the antiferromagnetic (AFM) spin ordering in symmetric nuclear matter with the effective Gogny interaction is studied within the framework of a Fermi liquid formalism. It is shown that the AFM spin polarization parameter of partially polarized nuclear matter for low enough temperatures increases with temperature. The entropy of the AFM spin state for some temperature range is larger than the entropy of the normal state. Nerveless, the free energy of the AFM spin state is always less than the free energy of the normal state and, hence, the AFM spin polarized state is preferable for all temperatures below the critical temperature.Comment: To appear in PRC; some references and comments adde

Antiferromagnetic spin phase transition in nuclear matter with effective Gogny interaction

The possibility of ferromagnetic and antiferromagnetic phase transitions in symmetric nuclear matter is analyzed within the framework of a Fermi liquid theory with the effective Gogny interaction. It is shown that at some critical density nuclear matter with D1S effective force undergoes a phase transition to the antiferromagnetic spin state (the opposite direction of neutron and proton spins). The self--consistent equations of spin polarized nuclear matter with D1S force have no solutions, corresponding to the ferromagnetic spin ordering (the same direction of neutron and proton spins) and, hence, the ferromagnetic transition does not appear. The dependence of antiferromagnetic spin polarization parameter as a function of density is found at zero temperature.Comment: Report at the workshop "Hot points in astrophysics and cosmology", Dubna, August, 2-13, 2004. REVTeX4, 9 pages, 3 figure

Unusual temperature behavior of entropy of antiferromagnetic spin state in nuclear matter with effective finite range interaction

The unusual temperature behavior of the entropy of the antiferromagnetic (AFM) spin state in symmetric nuclear matter with the Gogny D1S interaction, being larger at low temperatures than the entropy of nonpolarized matter, is related to the dependence of the entropy on the effective masses of nucleons in a spin polarized state. The corresponding conditions for comparing the entropies of the AFM and nonpolarized states in terms of the effective masses are formulated, including low and high temperature limits. It is shown that the unexpected temperature behavior of the entropy of the AFM spin state at low temperatures is caused by the violation of the corresponding low temperature criterium.Comment: version accepted for publication in PR

Spin polarized states in neutron matter at a strong magnetic field

Spin polarized states in neutron matter at a strong magnetic field are considered in the model with the Skyrme effective interaction (SLy4, SLy7 parametrizations). Analyzing the self-consistent equations at zero temperature, it is shown that a thermodynamically stable branch of solutions for the spin polarization parameter as a function of density corresponds to the negative spin polarization when the majority of neutron spins are oriented oppositely to the direction of the magnetic field. Besides, beginning from some threshold density being dependent on the magnetic field strength the self-consistent equations have also two other branches (upper and lower) of solutions for the spin polarization parameter with the positive spin polarization. The free energy corresponding to the upper branch turns out to be very close to the free energy corresponding to the thermodynamically preferable branch with the negative spin polarization. As a consequence, at a strong magnetic field, the state with the positive spin polarization can be realized as a metastable state at the high density region in neutron matter which under decreasing density at some threshold density changes into a thermodynamically stable state with the negative spin polarization. The calculations of the neutron spin polarization parameter and energy per neutron as functions of the magnetic field strength show that the influence of the magnetic field remains small at the field strengths up to $10^{17}$ G.Comment: Prepared with RevTeX4, 8pp., 5 figs; v.2: matches published versio

Spin polarized states in strongly asymmetric nuclear matter

In the framework of a Fermi liquid theory it is considered the possibility of appearance of spin polarized states in strongly asymmetric nuclear matter with Skyrme effective interaction. The zero temperature dependence of neutron and proton spin polarization parameters as functions of density is found for SLy4, SLy5 effective forces. It is shown that at some critical density it will be formed the state with the oppositely directed spins of neutrons and protons, while the state with the same direction of spins does not appear. In comparison with neutron matter, even small admixture of protons strongly decreases the threshold density of spin instability. It is clarified that protons become totally polarized within very narrow density domain while in the density profile of neutron spin polarization parameter their appear long tails near the transition density.Comment: Prepared with RevTeX4, 8p., 3 figures; to appear in PR

Skyrme Interaction and Nuclear Matter Constraints

This paper presents a detailed assessment of the ability of the 240 Skyrme interaction parameter sets in the literature to satisfy a series of criteria derived from macroscopic properties of nuclear matter in the vicinity of nuclear saturation density at zero temperature and their density dependence, derived by the liquid drop model, experiments with giant resonances and heavy-ion collisions. The objective is to identify those parameterizations which best satisfy the current understanding of the physics of nuclear matter over a wide range of applications. Out of the 240 models, only 16 are shown to satisfy all these constraints. Additional, more microscopic, constraints on density dependence of the neutron and proton effective mass beta-equilibrium matter, Landau parameters of symmetric and pure neutron nuclear matter, and observational data on high- and low-mass cold neutron stars further reduce this number to 5, a very small group of recommended Skyrme parameterizations to be used in future applications of the Skyrme interaction of nuclear matter related observables. Full information on partial fulfillment of individual constraints by all Skyrme models considered is given. The results are discussed in terms of the physical interpretation of the Skyrme interaction and the validity of its use in mean-field models. Future work on application of the Skyrme forces, selected on the basis of variables of nuclear matter, in Hartree-Fock calculation of properties of finite nuclei, is outlined.Comment: 86 pages, 14 figure

Competition of ferromagnetic and antiferromagnetic spin ordering in nuclear matter

In the framework of a Fermi liquid theory it is considered the possibility of ferromagnetic and antiferromagnetic phase transitions in symmetric nuclear matter with Skyrme effective interaction. The zero temperature dependence of ferromagnetic and antiferromagnetic spin polarization parameters as functions of density is found for SkM$^*$, SGII effective forces. It is shown that in the density domain, where both type of solutions of self--consistent equations exist, ferromagnetic spin state is more preferable than antiferromagnetic one.Comment: 9p., 3 figure

Phase transition to the state with nonzero average helicity in dense neutron matter

The possibility of the appearance of the states with a nonzero average helicity in neutron matter is studied in the model with the Skyrme effective interaction. By providing the analysis of the self-consistent equations at zero temperature, it is shown that neutron matter with the Skyrme BSk18 effective force undergoes at high densities a phase transition to the state in which the degeneracy with respect to helicity of neutrons is spontaneously removed.Comment: 4 pages, 3 figures; v2: journal versio