Density dependencies of interaction strengths and their influences on nuclear matter and neutron stars in relativistic mean field theory

Abstract

The density dependencies of various effective interaction strengths in the relativistic mean field are studied and carefully compared for nuclear matter and neutron stars. The influences of different density dependencies are presented and discussed on mean field potentials, saturation properties for nuclear matter, equations of state, maximum masses and corresponding radii for neutron stars. Though the interaction strengths and the potentials given by various interactions are quite different in nuclear matter, the differences of saturation properties are subtle, except for NL2 and TM2, which are mainly used for light nuclei, while the properties by various interactions for pure neutron matter are quite different. To get an equation of state for neutron matter without any ambiguity, it is necessary to constrain the effective interactions either by microscopic many-body calculations for the neutron matter data or the data of nuclei with extreme isospin. For neutron stars, the interaction with large interaction strengths give strong potentials and large Oppenheimer-Volkoff (OV) mass limits. The density-dependent interactions DD-ME1 and TW-99 favor a large neutron population due to their weak $\rho$-meson field at high densities. The OV mass limits calculated from different equations of state are 2.02 $\sim$ 2.81$ M_\odot$, and the corresponding radii are 10.78 $\sim$ 13.27 km. After the inclusion of the hyperons, the corresponding values become 1.52 $\sim$ 2.06 $M_\odot$ and 10.24 $\sim$ 11.38 km.