# Applicability of Relativistic Point-Coupling Models to Neutron Star Physics

## TL;DR

This paper assesses the use of relativistic point-coupling models for neutron star physics, comparing two functionals and highlighting the need for observational constraints to refine the models at high densities.

## Contribution

It demonstrates the application of relativistic point-coupling models to neutron star EoS and identifies divergences and limitations at high densities.

## Key findings

- Functional PC-PK1 shows suppressed pressure at high densities.
- Large divergences exist between the two functionals in neutron star predictions.
- Observational data like gravitational-wave tidal deformabilities are crucial for model improvement.

## Abstract

Comparing with a wide range of covariant energy density functional models based on the finite-range meson-exchange representation, the relativistic mean-field models with the zero-range contact interaction, namely the relativistic point-coupling models, are still infrequent to be utilized in establishing nuclear equation of state (EoS) and investigating neutron star properties, although comprehensive applications and achievements of them in describing many nuclear properties both in ground and exited states are mature. In this work, the EoS of neutron star matter is established constructively in the framework of the relativistic point-coupling models to study neutron star physics. Taking two selected functionals DD-PC1 and PC-PK1 as examples, nuclear symmetry energies and several neutron star properties including proton fractions, mass-radius relations, the core-crust transition density, the fraction of crustal moment of inertia and dimensionless tidal deformabilities are discussed. A suppression of pressure of neutron star matter found in the functional PC-PK1 at high densities results in the difficulty of its prediction when approaching to the maximum mass of neutron stars. In addition, the divergences between two selected functionals in describing neutron star quantities mentioned above are still large, ascribing to the less constrained behavior of these functionals at high densities. Then it is expected that the constraints on the dense matter EoS from precise and massive modern astronomical observations, such as the tidal-deformabilities taken from gravitational-wave events, would be essential to improve the parameterizing of the relativistic point-coupling models.