Anisotropic pressure in dense neutron matter under the presence of a strong magnetic field

Dense neutron matter with recently developed BSk19 and BSk21 Skyrme effective forces is considered in magnetic fields up to $10^{20}$ G at zero temperature. The breaking of the rotational symmetry by the magnetic field leads to the differentiation between the pressures along and perpendicular to the field direction which becomes significant in the fields $H>H_{th}\sim10^{18}$ G. The longitudinal pressure vanishes in the critical field $10^{18}<H_c\lesssim10^{19}$ G, resulting in the longitudinal instability of neutron matter. For the Skyrme force fitted to the stiffer underlying equation of state (BSk21 vs. BSk19) the threshold $H_{th}$ and critical $H_c$ magnetic fields become larger. The longitudinal and transverse pressures as well as the anisotropic equation of state of neutron matter are determined under the conditions relevant for the cores of magnetars.Comment: 7 pages, 3 figures; published online 7 December 201

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

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