Spin polarized neutron matter within the Dirac-Brueckner-Hartree-Fock approach

Abstract

The relation between energy and density (known as the nuclear equation of state) plays a major role in a variety of nuclear and astrophysical systems. Spin and isospin asymmetries can have a dramatic impact on the equation of state and possibly alter its stability conditions. An example is the possible manifestation of ferromagnetic instabilities, which would indicate the existence, at a certain density, of a spin-polarized state with lower energy than the unpolarized one. This issue is being discussed extensively in the literature and the conclusions are presently very model dependent. We will report and discuss our recent progress in the study of spin-polarized neutron matter. The approach we take is microscopic and relativistic. The calculated neutron matter properties are derived from realistic nucleon-nucleon interactions. This makes it possible to understand the properties of the equation of state in terms of specific features of the nuclear force model.

Finite temperature effects on anisotropic pressure and equation of state of dense neutron matter in an ultrastrong magnetic field

“…Such an attempt was made in the recent article [59] by attracting the ideas from the nuclear energy density functional theory. However, the constraints obtained in this study on the Skyrme force parameters lead to the unrealistic consequence that the effective masses of nucleons with spin up and spin down in a polarized state should be equal, contrary to the results of calculations with realistic NN interaction [29,31]. On the other hand, the observational data still do not rule out the existence of a ferromagnetic hadronic core inside a neutron star caused by spontaneous ordering of hadron spins (in this respect, see, e.g., Refs.…”

“…It was shown that the behavior of spin polarization of neutron matter in the high density region in a strong magnetic field crucially depends on whether neutron matter develops a spontaneous spin polarization (in the absence of a magnetic field) at several times nuclear matter saturation density, or the appearance of a spontaneous polarization is not allowed at the relevant densities (or delayed to much higher densities). The first case is usual for the Skyrme forces [13][14][15][16][17][18][19][20][21][22][23], while the second one is characteristic for the realistic nucleon-nucleon (NN) interaction [24][25][26][27][28][29][30][31][32]. In the former case, a ferromagnetic transition to a totally spin polarized state occurs while in the latter case a ferromagnetic transition is excluded at all relevant densities and the spin polarization remains quite low even in the high density region.…”

Properties of nuclear matter and finite nuclei with finite range simple effective interaction

“…From a fit to the DBHF predictions on effective mass splitting between spin-up and spin-down neutrons in spin polarized neutron matter [28], it is found that the SEI predictions agrees well with the DBHF ones for ε l,l ex = ε l ex /3, as shown in Ref. [17].…”

Spin- and isospin-polarized states of nuclear matter in the Dirac-Brueckner-Hartree-Fock model

“…The need to separate the interaction by spin components brings along angular dependence, with the result that the single-particle potential depends also on the direction of the momentum, although such dependence was found to be weak [33]. The G-matrix equation is solved using partial wave decomposition and the matrix elements are then summed as in Eq.…”