Proton fraction in the inner neutron-star crust

Abstract

Monte Carlo simulations of neutron-rich matter of relevance to the inner neutron-star crust are performed for a system of A = 5, 000 nucleons. To determine the proton fraction in the inner crust, numerical simulations are carried out for a variety of densities and proton fractions. We concludeas others have before us using different techniques-that the proton fraction in the inner stellar crust is very small. Given that the purported "nuclear pasta" phase in stellar crusts develops as a consequence of the long-range Coulomb interaction among protons, we question whether pasta formation is possible in such proton-poor environments. To answer this question, we search for physical observables sensitive to the transition between spherical nuclei and exotic pasta structures. Of particular relevance is the static structure factor S(k)-an observable sensitive to density fluctuations. However, no dramatic behavior was observed in S(k). We regard the identification of physical observables sensitive to the existence-or lack-thereof-of a pasta phase in proton-poor environments as an open problem of critical importance.

Neutron skin thickness from the measured electric dipole polarizability inNi68,Sn120, andRoca-Maza1, Viñas2, Centelles3 et al. 2015Phys. Rev. CSelf Cite233322563View full textAdd to dashboardCite

“…Although a robust correlation between the electric dipole polarizability and the neutron skin thickness was found [19], based on the droplet model it was shown that the correlation becomes significantly stronger for the product of the electric dipole polarizability and the nuclear symmetry energy coefficient J [20]. The correlation was indeed found to be very strong, but current uncertainties in the determination of J hinder the determination of the neutron skin thickness of 208 Pb.…”

“…Following the high-resolution measurement carried out at RCNP [12], two systematic studies of the electric dipole polarizability of 208 Pb were performed using a large set of nuclear EDFs [19,20]. Although a robust correlation between the electric dipole polarizability and the neutron skin thickness was found [19], based on the droplet model it was shown that the correlation becomes significantly stronger for the product of the electric dipole polarizability and the nuclear symmetry energy coefficient J [20].…”

“…For our systematic analysis of the electric dipole polarizability we employ a set of non-relativistic Skyrme interactions extensively used in the literature [46] [19,44]. Values of r = 0.65 and r = 0.94 for the respective correlation coefficients are also displayed.…”

“…In particular, the experimental determination of α D ( 208 Pb), combined with a covariance analysis performed with an optimized Skyrme functional ("SV-min"), predicted a neutron skin thickness in 208 Pb ∆r np = 0.156 +0.025 −0.021 fm [12]. In a subsequent systematic study performed with a large ensemble of both nonrelativistic and relativistic EDFs, a neutron skin thickness ∆r np = 0.168±0.022 fm was estimated [19]. By using relations deduced from the Droplet Model (DM), it was noted that the neutron skin thickness is correlated more strongly with the product of the electric dipole polarizability and the symmetry energy coefficient at saturation density (J), than to the dipole polarizability alone [20].…”

Recent progress in EDF-based methods applied to nuclear properties

“…Recently is has been shown that the dipole polarisability (how the energy of the nucleus changes in an external field) is correlated to the dipole response, the neutron skin and the slope of the EoS symmetry energy [43,44]. Several recent works also relate the neutron skin and the density dependence of the symmetry energy [45,46].…”