Quantum nuclear pasta and nuclear symmetry energy

Abstract

Complex and exotic nuclear geometries are expected to appear naturally in dense nuclear matter found in the crust of neutron stars and supernovae environment collectively referred to as "nuclear pasta". The pasta geometries depend on the average baryon density, proton fraction and temperature and are critically important in the determination of many transport properties of matter in supernovae and the crust of neutron stars. Using a set of self-consistent microscopic nuclear energy density functionals we present the first results of large scale quantum simulations of pasta phases at baryon densities 0.03 ≤ ρ ≤ 0.10 fm −3 , proton fractions 0.05 ≤ Yp ≤ 0.40, and zero temperature. The full quantum simulations, in particular, allow us to thoroughly investigate the role and impact of the nuclear symmetry energy on pasta configurations. We use the Sky3D code that solves the Skyrme Hartree-Fock equations on a three-dimensional Cartesian grid. For the nuclear interaction we use the state of the art UNEDF1 parametrization, which was introduced to study largely deformed nuclei, hence is suitable for studies of the nuclear pasta. Density dependence of the nuclear symmetry energy is simulated by tuning two purely isovector observables that are insensitive to the current available experimental data. We find that a minimum total number of nucleons A = 2000 is necessary to prevent the results from containing spurious shell effects and to minimize finite size effects. We find that a variety of nuclear pasta geometries are present in the neutron star crust and the result strongly depends on the nuclear symmetry energy. The impact of the nuclear symmetry energy is less pronounced as the proton fractions increase. Quantum nuclear pasta calculations at T = 0 MeV are shown to get easily trapped in meta-stable states, and possible remedies to avoid meta-stable solutions are discussed.

Extension of the nuclear landscape to hyperheavy nuclei

“…Thus, they cannot be formed in laboratory conditions and the only possible environment in which they can be produced is the ejecta of the mergers of neutron stars [73]. In a similar fashion, the regions of neutron stars with nuclear pasta phases [74][75][76] may be a breading ground for the formation of toroidal nuclei in the ejecta of the merger of neutron stars. The two-proton drip line for toroidal nuclei is characterized by neutron to proton ratio of N/Z ∼ 1.25.…”

Symmetry energy constraints from GW170817 and laboratory experiments

“…The influence of the EoS of neutron stars on the gravitational wave signal during inspiral is contained in the dimensionless constant called the tidal deformability or tidal polarizability,  = , where G is the gravitational constant, M and R are the mass and radius of a neutron star and k2 is the dimensionless Love number [6,8], which is also sensitive to the compactness parameter (M/R). As the knowledge of the mass-radius relation determines with high certainties the neutron-star matter EoS [9][10][11][12], information about EoS can be obtained from . [6] at 50% and 90% confidence levels.…”

Entrainment in Superfluid Neutron-Star Crusts: Hydrodynamic Description and Microscopic Origin

“…A few three-dimensional HF(+BCS) calculations of the ground-state of cold dense matter have been carried out [65,66], but are still prone to spurious shell effects due to the use of a cubic box with strictly periodic boundary conditions (this limitation has been recently analysed in Ref. [67]). …”