Antikaon condensation in magnetized neutron star matter within the framework of the $σ$-cut scheme

TL;DR

This work investigates how strong magnetic fields affect antikaon condensation in neutron star matter within an extended FSUGold relativistic mean-field model. It employs a $\sigma$-cut scheme to stiffen the high-density equation of state, enabling neutron stars to reach masses above $2M_{\odot}$ even in the presence of kaon condensation. The analysis incorporates Landau quantization for charged particles, baryon anomalous magnetic moments, and beta equilibrium with charge neutrality, and demonstrates that magnetic fields raise the $K^-$ onset density, while the $\sigma$-cut scheme offsets the softening due to condensation. The results indicate that appropriate choice of the $c_\sigma$ parameter yields neutron stars compatible with observational constraints, highlighting the interplay between magnetic fields, exotic phases, and high-density nuclear matter.

Abstract

This study investigates the effects of strong magnetic fields on antikaon condensation in neutron star matter using the extended FSUGold model model. It is found that the presence of strong magnetic fields alters the threshold density of antikaon condensation significantly, which means the threshold density of antikaon condensation is shifted to higher density compared with the magnetic field-free case. In the presence of strong magnetic fields, the equation of state (EoS) becomes stiffer than that of the zero field case. The effects of the $σ$-cut scheme on the EoS are also researched when the appearance of antikaon condensation is occurred. Through careful choice of the parameter of the $σ$-cut scheme, we are able to produce a maximum mass neutron star heavier than 2$M_{sun}$.

Figures (8)

• Figure 1: effective masses of nucleons and kaons versus baryon density using and not using the $\sigma$-cut scheme for the magnetic field strengths $B = 1.0\times 10^{18}$ G. The solid curves denote $M_N^*/M_N$, the dashed curves denote $m_K^*$. The values of $m_K^*$ as a function of baryon density are displayed on the vertical axis to the right of the figure.
• Figure 2: Kaon energy ($\omega_K$ ) and electron chemical potential ($\mu_e$) as a function of baryon density for $c_\sigma=0.3$. (Left panel) $B = 1.0 \times 10^{18}$ G; (right panel) $B = 1.0 \times 10^{19}$ G; The blue curves show $U_K$ = -160 MeV, green lines show $U_K$ = -140 MeV, and red lines show $U_K$ = -120 MeV.
• Figure 3: Relative population of particles versus baryon density for $K^-$ optical potential depth of $U_K = -$ 140 MeV and $c_\sigma=0.3$. (Upper panel) $B =0$ G; (lower panel) $B = 1.0 \times 10^{19}$ G.
• Figure 4: The kaon fraction as a function of the baryon density. (Upper panel) for $B =0, 1.0 \times 10^{18}$, and $1.0 \times 10^{19}$ G with fixed $U_K = -$ 140 MeV and $c_\sigma=0.3$; (middle panel) for $c_\sigma= 0.2, 0.3$ and 0.4 with fixed $U_K = -$ 140 MeV and $B = 1.0 \times 10^{18}$ G; (lower panel) for $U_K = -$ 120, $-$140 and $-$160 MeV with fixed $B = 1.0 \times 10^{18}$ G and $c_\sigma=0.3$.
• Figure 5: Pressure as a function of energy density. (Upper panel) using and not using the $\sigma$-cut scheme with fixed $U_K = -$140 MeV and $B =0$ G; (lower panel) for $B = 0, 1.0 \times 10^{18}$, and $1.0 \times 10^{19}$ G with fixed $U_K = -$140 MeV and $c_\sigma = 0.3$.