Influence of Finite-Nuclei Constraints on High-Density Transitions and Neutron Star Properties

TL;DR

This study integrates finite nuclei constraints into neutron star equation of state models, significantly narrowing the low-density EoS parameter space and impacting neutron star property predictions, especially for low-mass stars.

Contribution

It introduces a comprehensive method to incorporate finite nuclei data into EoS modeling, improving the reliability of high-density matter inferences from astrophysical observations.

Findings

Finite nuclei constraints reduce the low-density EoS parameter space by nearly half.

Inclusion of explicit FN constraints alters neutron star property predictions, notably for low-mass stars.

Some tension observed between model predictions and specific pulsar measurements.

Abstract

We construct posterior distributions of the equation of state (EoS) for matter beyond the inner crust of neutron stars by incorporating finite nuclei (FN) constraints within relativistic mean field models. These constraints are implemented in three complementary ways: (i) through theoretical bounds on the EoS, (ii) implicitly via nuclear matter parameters, and (iii) explicitly by enforcing consistency with experimental binding energies and charge radii of selected nuclei. The resulting low-density nucleonic EoSs are subsequently matched to a model-agnostic speed-of-sound parametrization, constrained by astrophysical observations, including NICER mass-radius measurements, tidal deformability limits from GW170817, and lower bounds on the maximum neutron-star mass inferred from radio pulsar observations. We find that the admissible range of the transition density is strongly sensitive to the choice of the low-density EoS. In particular, the inclusion of explicit FN constraints significantly reduces the allowed parameter space of the nucleonic EoS at low densities, narrowing the transition-density range by nearly a factor of two. Consequently, neutron-star properties inferred from EoSs with explicit FN constraints differ substantially, with especially pronounced effects for low-mass neutron stars and their correlations with nuclear matter parameters. A quantitative comparison, using metrics based on Mahalanobis distance, shows consistency of the explicit constraints with PSRs J0740+6620, J0030+0451, and J0437-4715, but suggest a possible tension with PSR J0614-3329. These findings underscore the critical importance of a consistent treatment of finite-nuclei properties for reliably inferring the behavior of high-density matter and the presence of possible phase transitions from astrophysical observations.