Imprint of the symmetry energy on the inner crust and strangeness content of neutron stars

TL;DR

This paper investigates how the symmetry energy influences various properties of neutron stars, including crust-core transition, pasta phase, and strangeness content, revealing correlations with the slope parameter L.

Contribution

It provides new insights into the impact of symmetry energy parameters on neutron star structure and composition, especially on the crust, pasta phase, and hyperon emergence.

Findings

Transition density and proton fraction correlate with slope parameter L.

Size of pasta clusters depends on the density dependence of symmetry energy.

Strangeness content and hyperon appearance are influenced by the symmetry energy slope.

Abstract

In this work we study the effect of the symmetry energy on several properties of neutron stars. First, we discuss its effect on the density, proton fraction and pressure of the neutron star crust-core transition. We show that whereas the first two quantities present a clear correlation with the slope parameter $L$ of the symmetry energy, no satisfactory correlation is seen between the transition pressure and $L$. However, a linear combination of the slope and curvature parameters at $\rho=0.1$ fm$^{-3}$ is well correlated with the transition pressure. In the second part we analyze the effect of the symmetry energy on the pasta phase. It is shown that the size of the pasta clusters, number of nucleons and the cluster proton fraction depend on the density dependence of the symmetry energy: a small $L$ gives rise to larger clusters. The influence of the equation of state at subsaturation densities on the extension of the inner crust of the neutron star is also discussed. Finally, the effect of the effect of the density dependence of the symmetry energy on the strangeness content of neutron stars is studied in the last part of the work. It is found that charged (neutral) hyperons appear at smaller (larger) densities for smaller values of the slope parameter $L$. A linear correlation between the radius and the strangeness content of a star with a fixed mass is also found.