Equation of state of neutron star matter, and the nuclear symmetry energy

Abstract

The nuclear mean-field potentials obtained in the Hartree-Fock method with different choices of the in-medium nucleon-nucleon (NN) interaction have been used to study the equation of state (EOS) of the neutron star (NS) matter. The EOS of the uniform NS core has been calculated for the npeµ composition in the β-equilibrium at zero temperature, using version Sly4 of the Skyrme interaction as well as two density-dependent versions of the finite-range M3Y interaction (CDM3Yn and M3Y-Pn), and versions D1S and D1N of the Gogny interaction. Although the considered effective NN interactions were proven to be quite realistic in numerous nuclear structure and/or reaction studies, they give quite different behaviors of the symmetry energy of nuclear matter at supranuclear densities that lead to the soft and stiff scenarios discussed recently in the literature. Different EOS's of the NS core and the EOS of the NS crust given by the compressible liquid drop model have been used as input of the Tolman-Oppenheimer-Volkov equations to study how the nuclear symmetry energy affects the model prediction of different NS properties, like the cooling process as well as the gravitational mass, radius, and moment of inertia.

Extended Hartree-Fock study of the single-particle potential: The nuclear symmetry energy, nucleon effective mass, and folding model of the nucleon optical potential

“…The behavior of the EOS of the asymmetric NM with the increasing n/p asymmetries shown in Fig. 1 is typical and similar to those observed earlier in the HF calculations of the NM using the different types of the in-medium (density dependent) NN interaction [15][16][17].…”

“…These medium effects are usually considered as the main physics origin of an explicit density dependence embedded in the different versions of the effective NN interaction, being used currently in the HF calculations of the nuclear structure or nuclear reaction studies. Among them, quite popular are the density dependent versions of the M3Y interaction (originally constructed to reproduce the G-matrix elements of the Reid [11] and Paris [12] NN potentials in an oscillator basis), which have been successfully used in the HF studies of the NM [13][14][15][16][17] as well as in the folding model studies of the nucleon-nucleus and nucleus-nucleus scattering [18][19][20][21][22][23].…”

Influence of the single-particle structure on the nuclear surface and the neutron skin

“…This quantity is strongly correlated, within the realm of nuclear mean-field theories [18,[31][32][33][34][35][36][37][38], with the slope of the nuclear symmetry energy at saturation density, and therefore may be used to constrain the equation of state of neutron-rich matter. Thus, the results of the investigation of the distribution of neutrons in atomic nuclei affect studies of such distant areas of physics as heavy-ion collisions [39][40][41][42], scattering of polarized electrons on nuclei [15,36,[43][44][45][46][47], precision tests of the standard model by atomic parity violation [48,49], and nuclear astrophysics [50][51][52][53][54]. Theoretical predictions of neutron density distributions can be verified, in principle, by the comparison of the calculated values of the neutron rms radii and of the NST with the available experimental data.…”

Density dependence of the symmetry energy from neutron skin thickness in finite nuclei

“…The symmetry energy is also relevant for some aspects of fundamental physics because it has implications for atomic parity non-conserving observables involved in low-energy tests of the Standard Model and new physics [22,23]. In astrophysics the symmetry energy is very important for understanding different properties of neutron stars, supernova explosions, and stellar nucleosynthesis [1,[24][25][26].…”