Nuclear Matter and Neutron Stars from Relativistic Brueckner-Hartree-Fock Theory

TL;DR

This paper uses the full Dirac space RBHF theory with realistic Bonn potentials to study nuclear matter and neutron star properties, providing new insights into the equation of state and observational consistency.

Contribution

It introduces a systematic investigation of nuclear matter and neutron star properties using RBHF theory in the full Dirac space, including negative-energy states, which improves upon previous positive-energy state calculations.

Findings

Predicts neutron star radii around 12 km for 1.4 solar masses.

Determines the density threshold for the direct URCA process in neutron stars.

Finds the full-Dirac-space RBHF predicts the softest symmetry energy, aligning better with gravitational wave data.

Abstract

The momentum and isospin dependence of the single-particle potential for the in-medium nucleon are the key quantities in the Relativistic Brueckner-Hartree-Fock (RBHF) theory. It depends on how to extract the scalar and the vector components of the single-particle potential inside nuclear matter. In contrast to the RBHF calculations in the Dirac space with the positive-energy states (PESs) only, the single-particle potential can be determined in a unique way by the RBHF theory together with the negative-energy states (NESs), i.e., the RBHF theory in the full Dirac space. The saturation properties of symmetric and asymmetric nuclear matter in the full Dirac space are systematically investigated based on the realistic Bonn nucleon-nucleon potentials. In order to further specify the importance of the calculations in the full Dirac space, the neutron star properties are investigated. The direct URCA process in neutron star cooling will happen at density $\rho_{\rm{DURCA}}=0.43,~0.48,~0.52$ fm$^{-3}$ with the proton fractions $Y_{p,\rm{DURCA}}=0.13$. The radii of a $1.4M_\odot$ neutron star are predicated as $R_{1.4M_\odot}=11.97,~12.13,~12.27$ km, and their tidal deformabilities are $\Lambda_{1.4M_\odot}=376,~405,~433$ for potential Bonn A, B, C. Comparing with the results obtained in the Dirac space with PESs only, full-Dirac-space RBHF calculation predicts the softest symmetry energy which would be more favored by the gravitational waves (GW) detection from GW170817. Furthermore, the results from full-Dirac-space RBHF theory are consistent with the recent astronomical observations of massive neutron stars and simultaneous mass-radius measurement.