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Properties of neutron stars and strangeness-mixed stars from a pion mean-field approach

Nam-Yong Ghim1,*, Hyun-Chul Kim1,2,†, Ulugbek Yakhshiev1,3,‡, and Ghil-Seok Yang4,§

  • *Contact author: Namyong.gim@inha.edu
  • †Contact author: hchkim@inha.ac.kr
  • ‡Contact author: yakhshiev@inha.ac.kr
  • §Contact author: ghsyang@hoseo.edu
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Phys. Rev. D 112, 043031 – Published 25 August, 2025

DOI: https://doi.org/10.1103/br33-9v2r

Abstract

We investigate the properties of the static neutron stars and strangeness-mixed stars, based on the equations of state derived from a pion mean-field approach. Using the empirical data on the pion-nucleus scattering and bulk properties of nuclear matter, we have already fixed all of the parameters in a previous work, where the nucleons and hyperons were shown to be modified in various nuclear media. In the current work, we first examine the energy and pressure inside a neutron star. We show that the central densities in various neutron stars vary within the range of (3–4)ρ0, where ρ0 is the normal nuclear matter density. The mass-radius relations are obtained and discussed. As the slope parameter for neutron matter increases, the radii of the neutron stars increase with their masses fixed. We also study the strangeness-mixed stars or the hyperon stars using the same sets of parameters. As the strangeness content of strange matter increases, the binding energy per nucleon is saturated and the corresponding equation of state becomes softened. Consequently, the central densities of the strangeness-mixed stars increase. Assuming that recently observed neutron stars are the strangeness-mixed ones, we find that the central densities increase.

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Phys. Rev. D 112, 043031– Published 25 August, 2025
  • Received 16 July 2024
  • Revised 13 July 2025
  • Accepted 22 July 2025
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