Sensitivity of neutron drip lines and neutron star properties to the symmetry energy

Abstract

We investigate the influence of the nuclear symmetry energy and its density slope parameter on the neutron dripline and neutron star properties using a semi-classical liquid drop model (LDM) and energy density functionals constrained by chiral effective field theory. To analyze finite nuclei and mass tables, the nuclear symmetry energy at saturation density is fixed, and the surface tension is determined to minimize the root-mean-square deviation of the total binding energy for 2208 nuclei. Correlations between symmetry energy parameters and neutron driplines, crust-core transition densities, and the radii of $1.4\,\msun$ neutron stars are explored using the LDM framework. Additionally, we examine the relationship between macroscopic properties, such as neutron star radii ($R_{1.4}$), and microscopic properties, including the number of isotopes and the last bound nucleus for $Z=28$, within the LDM context.

Figures (14)

• Figure 1: Total binding energy difference between the LDM and experiment for given mass number (left) and isospin asymmetry (right).
• Figure 2: Neutron drip lines constructed from the incompressible LDM (pink squares) and the compressible liquid drop model (curves) up to $Z=120$ for fixed $L$ and varying $S_v$.
• Figure 3: Neutron drip lines constructed from the incompressible LDM (pink squares) and the compressible liquid drop model (curves) up to $Z=120$ for fixed $S_v$ and varying $L$.
• Figure 4: The symmetry energy parameters from various nuclear mass models. The ellipse constraints from the chiral effective calculations and astrophysical observations is added.
• Figure 5: One-neutron and two-neutron separation energies for nickel isotopes in the compressible liquid drop model, neglecting shell effects (top panel) and including shell effects (bottom panel). In each panel, the LDM models have varying $S_v$, with $L=50$ MeV held fixed.