Dependence of relative abundances of constituents in dense stellar matter on nuclear symmetry energy

TL;DR

This paper investigates how the nuclear symmetry energy influences the composition and phase transitions in dense stellar matter, revealing that kaon condensation is not necessarily linked to the EOS stiffness beyond nuclear saturation density.

Contribution

It demonstrates the strong dependence of lepton chemical potentials and constituent abundances on the nuclear symmetry energy, challenging previous assumptions about kaon condensation.

Findings

Electron chemical potential depends on nuclear symmetry energy.

Relative abundances of particles are sensitive to the symmetry energy.

Kaon condensation is not directly tied to the EOS stiffness beyond n_0.

Abstract

For a dense stellar matter, which is electrically neutral and in beta equilibrium, the electron chemical potential, mu_e, will depend nontrivially on baryonic matter density. It is generally expected that as density increases, the electron chemical potential will increase and new degrees of freedom will emerge as mu_e becomes comparable to their energy scales. Assuming the electrical neutrality and beta equilibrium for the stellar matter, we have studied how the density dependence of lepton chemical potentials varies for different models of nuclear interactions that are constrained by experiments up to nuclear matter density, n_0, but extrapolate differently(unconstrained) beyond n_0 and calculated the relative abundances of nucleons(neutron and proton) and leptons(electron and muon) and their density dependencies. We find that the density dependence of the electron chemical potential is strongly dependent on the structure of the nuclear symmetry energy relevant to softness/stfness of the nuclear matter EOS that measures the energy relevant to the neutron-proton asymmetry. As a consequence, the relative abundances of neutrons, protons, electrons, and muons as well as the kaon condensation are strongly dependent on the nuclear symmetry energy. An intriguing result in our finding is that contrary to the accepted lore, kaon condensation in neutron star matter, which is considered to be the first phase transitions beyond n_0 and plays a crucial role in certain scenarios of compact-star formation, is not directly tied to the softness or stiffness of the EOS beyond n_0. This point is illustrated with a "super-soft" EOS that is fit to the pi^-/pi^+ ratio data of GSI which excludes kaon condensation at any density.