Equation of state for neutron stars in SU(3) flavor symmetry

Using several relativistic mean-field models (such as GM1, GM3, NL3, TM1, FSUGold, and IU-FSU) as well as the quark-meson coupling model, we calculate the particle fractions, the equation of state, the maximum mass, and radius of a neutron star within relativistic Hartree approximation. We also discuss in detail the role of nonlinear potentials involved in the mean-field models. In determining the couplings of the isoscalar, vector mesons to the octet baryons, we examine the extension of SU(6) spin-flavor symmetry to SU(3) flavor symmetry. Furthermore, we consider the strange (${\sigma }^{*}$ and $\varphi$) mesons and study how they affect the equation of state. We find that the equation of state in SU(3) symmetry can sustain a neutron star with mass of $(1.8\sim 2.1)M_{\odot }$, even if hyperons exist inside the core. It is noticeable that the strange vector ($\varphi$) meson and the variation of baryon substructure in matter also play important roles in supporting a massive neutron star.

Figure 1

Particle fractions, $Y_i$, in the QMC and CQMC models (left panel, QMC; right panel, CQMC). As explained in the text, in each panel, figure (a) is for the case where only the nonstrange mesons ($\sigma$, $\omega$, and $\rho$) are considered in SU(6) symmetry; figure (b) is for the case where all the mesons, including the ${\sigma }^{*}$ and $\varphi$, are considered in SU(6) symmetry; and figure (c) is for the case where all the mesons are included in SU(3) symmetry.

Figure 2

Particle fractions, $Y_i$, in the GM1, GM3, NL3, and TM1 models (upper left panel, GM1; upper right panel, GM3; lower left panel, NL3; lower right panel, TM1). The labels (a), (b), and (c) in the figures are the same as described in the legend of Fig. 1.

Figure 3

Particle fractions, $Y_i$, in the FSUGold and IU-FSU models (left panel, FSUGold; right panel, IU-FSU). The labels (a), (b), and (c) are the same as described in the legend of Fig. 1.

Figure 4

Meson fields in the QMC and CQMC models (left panel, QMC; right panel, CQMC). The labels (a), (b), and (c) are the same as described in the legend of Fig. 1.

Figure 5

Meson fields in the GM1, GM3, NL3, and TM1 models (upper left panel, GM1; upper right panel, GM3; lower left panel, NL3; lower right panel, TM1). The labels (a), (b), and (c) are the same as described in the legend of Fig. 1.

Figure 6

Meson fields in the FSUGold and IU-FSU models (left panel, FSUGold; right panel, IU-FSU). The labels (a), (b), and (c) are the same as described in the legend of Fig. 1.

Figure 7

Equations of state in the QMC and CQMC models. The labels (a), (b), and (c) are the same as described in the legend of Fig. 1.

Figure 8

Equations of state in the GM1, GM3, NL3, and TM1 models (left panel, GM1 and GM3; right panel, NL3 and TM1). The labels (a), (b), and (c) are the same as described in the legend of Fig. 1.

Figure 9

Equations of state in the FSUGold and IU-FSU models. The labels (a), (b), and (c) are the same as described in the legend of Fig. 1.

Figure 10

Mass-radius relations in the QMC and CQMC models. The labels (a), (b), and (c) are the same as described in the legend of Fig. 1.

Figure 11

Mass-radius relations in the GM1, GM3, NL3, and TM1 models (left panel, GM1 and GM3; right panel, NL3 and TM1). The labels (a), (b), and (c) are the same as described in the legend of Fig. 1. In the NL3 model, the (red) solid curve for SU(3) symmetry does not yet reach the maximum point because the nucleon mass in matter becomes negative at the endpoint.

Figure 12

Mass-radius relations in the FSUGold and IU-FSU models. The labels (a), (b), and (c) are the same as described in the legend of Fig. 1.