Impact of Effective Nucleon Mass and Multineutron States on the Equation of State for Core-Collapse Supernovae

TL;DR

This paper examines how effective nucleon mass and multineutron states influence the equation of state in core-collapse supernovae, affecting nuclear composition and thermodynamic properties.

Contribution

It introduces new equations of state considering multineutron states and analyzes their effects on nuclear composition and thermodynamics in supernova conditions.

Findings

Larger effective nucleon mass slightly alters nuclear composition due to symmetry energy differences.

Multineutron states significantly reduce unbound neutron fractions at high densities.

Chemical potential shifts promote formation of heavier nuclei, lowering free energy.

Abstract

In this study, we investigate the impact of effective nucleon mass and the existence of the dineutron $(\mathrm{^{2}n})$ and the tetraneutron $(\mathrm{^{4}n})$ on the thermodynamic properties and nuclear compositions by constructing new equations of state. Our results indicate that the model with a larger effective nucleon mass slightly alters the nuclear composition in neutron-rich environments primarily due to differences in the symmetry energy: the mass fractions of unbound neutrons, protons, and heavy nuclei increase. The impact on the thermodynamic properties is negligible, except for the chemical potentials. On the other hand, multineutron states become prominent at high densities in neutron-rich environments, leading to a substantial reduction in the unbound neutron fraction. This depletion lowers the chemical potential of unbound neutrons, which in turn reduces the abundance of neutron-rich nuclei. Consequently, the number of unbound protons increases, leading to a corresponding rise in proton chemical potential. These shifts in chemical potentials promote the formation of heavy nuclei with larger mass and atomic numbers. Ultimately, this compositional shift results in a lower free energy, primarily driven by the emergence of these heavy nuclei.