Nuclear equation of state and finite nucleon volumes

TL;DR

This paper introduces a modified relativistic mean field model incorporating nucleon volume corrections via enthalpy, resulting in a softer equation of state that aligns with empirical data and supports massive neutron star observations.

Contribution

It proposes a novel approach to include nucleon volume effects in the EoS using enthalpy, improving agreement with empirical and DBHF results.

Findings

The model produces a softer EoS consistent with semi-empirical estimates.

It accurately predicts neutron star masses up to ~2 solar masses.

The model maintains proper saturation properties and compressibility.

Abstract

It is shown how the Equation of State (EoS) depends on nucleon properties inside Nuclear Matter (NM). We propose to benefit from the concept of enthalpy in order to include volume corrections to the nucleon rest energy, which are proportional to pressure and absent in a standard Relativistic Mean Field (RMF) with point-like nucleons. As a result, the nucleon mass can decrease inside NM, making the model nonlinear and the EoS softer. The course of the EoS in our RMF model agrees with a semi-empirical estimate and is close to the results obtained from extensive DBHF calculations with a Bonn A potential, which produce an EoS stiff enough to describe neutron star properties (mass--radius constraint), especially the masses of PSR J1614_2230 and PSR J0348_0432, known as the most massive ($\sim 2 M_\odot$) neutron stars. The presented model has proper saturation properties, including a good value of compressibility.