Properties of Neutron Star Crust with Improved Nuclear Physics: Impact of Chiral EFT Interactions and Experimental Nuclear Masses

Abstract

A compressible liquid-drop approach adjusted to uniform matter many-body calculations based on chiral EFT interactions and to the experimental nuclear masses is used to investigate the neutron star crust properties. Eight chiral EFT hamiltonians and a representative phenomenological force (SLy4) are confronted. We show that some properties of the crust, e.g. clusters mass, charge, and asymmetry, are mostly determined by symmetric matter properties close to saturation density and are therefore mainly constrained by experimental nuclear masses, while other properties, e.g., energy per particle, pressure, sound speed, are mostly influenced by low-density predictions in neutron matter, where chiral EFT and phenomenological forces substantially differ.

Confronting a set of Skyrme and $χ_{EFT}$ predictions for the crust of neutron stars

“…As already suggest in Ref. [18], these quantities are sensitive to the properties of low-density NM, as shown in Fig. 1.…”

“…[36], while the ones based on χEFT are very consistent among each other. In a previous analysis [18], we have compared in detail the χEFT predictions and the SLy4 Skyrme model, which is almost identical to the SLy5 presented here. By investi- gating other Skyrme models, which perform rather well for the ground state of finite nuclei, we now explore more widely the Skyrme's uncertainties in the predictions for the properties of low-density NM.…”

“…In the CLDM, the EoS used in the core is unified with the crust, through the bulk and neutron fluid contributions, see for instance the recent Refs. [17,18] and references therein. The effects of non-uniformities in the crust are implemented through finite-size (FS) terms.…”

“…A first comparison of the χEFT predictions against a representative phenomenological model, SLy4 [21], was performed in Ref. [18]. In this paper, we perform a more extensive comparison considering a set of seven Skyrme parametrisations which are used to determine the properties of finite nuclei, and perform pretty well.…”

Investigating Possible Existence of Hyper-Heavy Nuclei in Neutron Star Environment

“…They show that the total number of nucleons per unit cell (containing one nucleus), which is given by A cell = N + Z + N out (N out is the number of neutrons with single particle energy > 0), in the cell reaches in all the mentioned cases very high values (A cell >> 100). Moreover, in a recent study [10], the authors, using the more elaborated χ EFT Hamiltonian and the SLy4 phenomenological force, calculated the composition of the neutron star crust. In particular they predicted the cluster mass number A cl and proton number Z cl through the crust, which correspond to the masses and proton numbers associated to the nuclear cluster only (excluding the neutron fluid contribution).…”