Medium effects of magnetic moments of baryons on neutron stars under strong magnetic fields

We investigate medium effects due to density-dependent magnetic moments of baryons on neutron stars under strong magnetic fields. If we allow the variation of anomalous magnetic moments (AMMs) of baryons in dense matter under strong magnetic fields, AMMs of nucleons are enhanced to be larger than those of hyperons. The enhancement naturally affects the chemical potentials of baryons to be large and leads to the increase of a proton fraction. Consequently, it causes the suppression of hyperons, resulting in the stiffness of the equation of state. Under the presumed strong magnetic fields, we evaluate relevant particles’ population, the equation of state and the maximum masses of neutron stars by including density-dependent AMMs and compare them with those obtained from AMMs in free space.

💡 Research Summary

This paper investigates how density‑dependent anomalous magnetic moments (AMMs) of baryons influence the internal composition, equation of state (EOS), and maximum mass of neutron stars subjected to extremely strong magnetic fields. The authors adopt a relativistic mean‑field (RMF) framework that includes the full baryon octet (p, n, Λ, Σ⁰, Σ⁺, Σ⁻, Ξ⁰, Ξ⁻) together with leptons, and they impose β‑equilibrium and charge neutrality. In conventional neutron‑star modeling, the AMMs of baryons are taken as their vacuum (free‑space) values. However, theoretical arguments suggest that in dense matter under a magnetic field of order 10¹⁸ G, the internal quark structure of baryons can be deformed, leading to an enhancement of their magnetic moments. To capture this effect, the authors introduce a phenomenological density‑dependent AMM (DD‑AMM) prescription:

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