Neutron star cooling: A challenge to the nuclear mean field

Abstract

The two recent density-dependent versions of the finite-range M3Y interaction (CDM3Yn and M3Y-Pn) have been probed against the bulk properties of asymmetric nuclear matter (NM) in the nonrelativistic Hartree Fock (HF) formalism. The same HF study has also been done with the famous Skyrme (SLy4) and Gogny (D1S and D1N) interactions which were well tested in the nuclear structure calculations. Our HF results are compared with those given by other many-body calculations like the Dirac-Brueckner Hartree-Fock approach or ab-initio variational calculation using free nucleon-nucleon interaction, and by both the nonrelativistic and relativistic mean-field studies using different model parameters. Although the two considered density-dependent versions of the M3Y interaction were proven to be quite realistic in the nuclear structure or reaction studies, they give two distinct behaviors of the NM symmetry energy at high densities, like the Asy-soft and Asy-stiff scenarios found earlier with other mean-field interactions. As a consequence, we obtain two different behaviors of the proton fraction in the β-equilibrium which in turn can imply two drastically different mechanisms for the neutron star cooling. While some preference of the Asy-stiff scenario was found based on predictions of the latest microscopic many-body calculations or empirical NM pressure and isospin diffusion data deduced from heavy-ion collisions, a consistent mean-field description of nuclear structure database is more often given by some Asy-soft type interaction like the Gogny or M3Y-Pn ones. Such a dilemma poses an interesting challenge to the modern mean-field approaches.

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].…”

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

“…Based on the physics constraints implied by such studies, extrapolation is often made to draw conclusion on the low-and high-density behavior of S(n b ). However, such conclusions still remain quite divergent in some cases [23]. One of the most intriguing issues discussed recently in the literature is whether the "soft" or "stiff" density dependence of the NM symmetry energy is more realistic.…”

“…[23], the behavior of the density dependence of the proton fraction x p (n b ) plays a very important role in the determination of the NS cooling rate.…”

Origin of the neutron skin thickness ofPb208in nuclear mean-field models

“…By reason of its close connections with the nuclear symmetry energy, knowing accurately r np of 208 Pb can have important implications in diverse problems of nuclear structure and of heavy-ion reactions, in studies of atomic parity violation, as well as in the description of neutron stars and in other areas of nuclear astrophysics (see, e.g., Refs. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]). Since the charge radius of 208 Pb has been measured with extreme accuracy (r ch = 5.5013(7) fm [1]), the neutron rms radius of 208 Pb is the principal unknown piece of the puzzle.…”