-
The RMF model was constructed based on the one-boson-exchange picture for the nucleon-nucleon (
$ NN $ ) interaction. In the early version, there were only scalar ($ \sigma $ ) and vector mesons ($ \omega $ ), which present the attractive and repulsive components of$ NN $ interaction, respectively[100]. Then, the nonlinear terms of$ \sigma $ meson were introduced to reduce the incompressibility of nuclear matter[101]. The isovector meson,$ \rho $ was introduced to correctly describe the neutron star matter[102]. The nonlinear term of$ \omega $ meson[103] and the coupling terms between the$ \omega $ and$ \rho $ mesons[104] were also included to improve the high-density behaviors of nuclear matter and density-dependence of symmetry energy, respectively. Furthermore, a density-dependent RMF (DDRMF) model[105] was proposed based on the developments of Relativistic Brueckner-Hartree-Fock(RBHF) model. When the masses of exchanging mesons are regarded as infinite, the$ NN $ interaction is simplified as contact potential, which generates the point-coupling RMF (PCRMF) models[106].In the nonlinear RMF (NLRMF) model, the baryons interact with each other via exchanging various light mesons, including scalar-isoscalar meson (
$ \sigma $ ) with mass$ m_{\sigma} $ , vector-isoscalar meson ($ \omega $ ) with mass$ m_{\omega} $ , vector-isovector meson ($ \rho $ ) with mass$ m_{\rho} $ , and strange scalar and vector mesons ($ \sigma^* $ and$ \phi $ ) with mass$ m_{\sigma^*} $ and$ m_{\phi} $ , respectively[107-112]. The baryons considered in the present calculation are nucleons ($ n $ and$ p $ ) and hyperons ($ \varLambda,\; \varSigma,\; \varXi $ ). The Lagrangian density of NLRMF model is written as$$ \begin{split} {\cal{L}}_{{\rm{NL}}} = & \sum\limits_{{\rm{B}}}\overline{\psi}_{{\rm{B}}}\bigg[{{\rm{i}}}\gamma^{\mu}\partial_{\mu}-\left(M_{{\rm{B}}}-g_{\sigma {\rm{B}}}\sigma- g_{\sigma^* {\rm{B}}}\sigma^*\right)-\\& \gamma^{\mu}\Big(g_{\omega {\rm{B}}}\omega_{\mu}+g_{\phi {\rm{B}}}\phi_{\mu} +\dfrac{1}{2}g_{\rho {\rm{B}}}{\boldsymbol{\tau}}{\boldsymbol{\rho}}_{\mu}\Big)\bigg]\psi_{{\rm{B}}}+\\& \dfrac{1}{2}\partial^{\mu}\sigma\partial_{\mu}\sigma-\dfrac{1}{2}m_{\sigma}^2\sigma^2-\dfrac{1}{3}g_{2}\sigma^3 -\dfrac{1}{4}g_{3}\sigma^4+\\ & \dfrac{1}{2}\partial^{\mu}\sigma^*\partial_{\mu}\sigma^*-\dfrac{1}{2}m_{\sigma^*}^2\sigma^{*2}-\\ & \dfrac{1}{4}W^{\mu\nu}W_{\mu\nu}+\dfrac{1}{2}m_{\omega}^2\omega^{\mu}\omega_{\mu}+\dfrac{1}{4}c_3\left(\omega^{\mu}\omega_{\mu}\right)^2-\\& \dfrac{1}{4}\varPhi^{\mu\nu}\varPhi_{\mu\nu}+\dfrac{1}{2}m_{\phi}^2\phi^{\mu}\phi_{\mu}-\\& \dfrac{1}{4}{\boldsymbol{R}}^{\mu\nu}{\boldsymbol{R}}_{\mu\nu}+\dfrac{1}{2}m_{\rho}^2{\boldsymbol{\rho}}^{\mu}{\boldsymbol{\rho}}_{\mu}+\\& \varLambda_{{\rm{v}}}\left({g^2_{\omega N}}\omega^{\mu}\omega_{\mu}\right)\left({g^2_{\rho N}}{\boldsymbol{\rho}}^{\mu}{\boldsymbol{\rho}}_{\mu}\right), \end{split} $$ (1) where
$ \psi_{{\rm{B}}} $ represents the wave function of baryons with mass$ M_{{\rm{B}}} $ .$ \sigma,\; \sigma^*,\; \omega_{\mu},\; \phi_{\mu}\; {\boldsymbol{\rho}}_\mu $ denotes the fields of$ \sigma,\; \sigma^*, \; \omega,\; \phi $ , and$ \rho $ mesons, respectively.$ W_{\mu\nu} $ ,$ \varPhi_{\mu\nu} $ , and$ {\boldsymbol{R}}^{\mu\nu} $ are the anti-symmetry tensor fields of$ \omega $ ,$ \phi $ , and$ \rho $ mesons, which are given by$W^{\mu\nu} = \partial^{\mu}\omega^{\nu}-\partial^{\nu}\omega^{\mu}, \; \varPhi^{\mu\nu} = \partial^{\mu}\phi^{\nu}- \partial^{\nu}\phi^{\mu}, {\boldsymbol{R}}^{\mu\nu} = \partial^{\mu}{\boldsymbol{\rho}}^{\nu}-\partial^{\nu}{\boldsymbol{\rho}}^{\mu} -g_{\rho}({\boldsymbol{\rho}}^{\mu}\times{\boldsymbol{\rho}}^{\nu}).$ $ g_{i{\rm B}}\; (i = \omega,\; \phi,\; \rho) $ denotes the coupling constant between$ i $ meson and baryons, while$ g_{\omega N} $ and$ g_{\rho N} $ for the coupling strength between$ \omega,\; \rho $ meson and nucleon.$ g_2 $ and$ g_3 $ are the self-coupling terms for the$ \sigma $ meson and the coupling constant$ c_3 $ is for the$ \omega $ meson to reproduce the feature of the RBHF theory[103]. The nonlinear coupling constant$ \varLambda_{{\rm{v}}} $ was included to modify the density dependence of the symmetry energy[113]. To solve the nuclear many-body system in the framework of the NLRMF model, the mean-field approximation should be adopted, in which various mesons are treated as classical fields,$$ \begin{split} & \sigma\; \rightarrow\left\langle\sigma\right\rangle\equiv\sigma, \quad \sigma^*\; \rightarrow\left\langle\sigma^*\right\rangle\equiv\sigma^*,\\& \omega_{\mu}\rightarrow\left\langle\omega_{\mu}\right\rangle\equiv\omega, \quad \phi_{\mu}\rightarrow\left\langle\phi_{\mu}\right\rangle\equiv\phi,\\& {\boldsymbol{\rho}}_{\mu}\rightarrow\left\langle{\boldsymbol{\rho}}_{\mu}\right\rangle\equiv\rho. \end{split}$$ (2) The space components of the vector mesons are removed in the parity conservation system. In addition, the spatial derivatives of baryons and mesons are neglected in the infinite nuclear matter due to the transformation invariance. Finally, with the Euler-Lagrange equation, the equations of motion for baryons and mesons are obtained,
$$ \begin{split} & \left[{{\rm{i}}}\gamma^{\mu}\partial_{\mu}-M_{{\rm{B}}}^*-\gamma^0\left(g_{\omega{\rm{B}}}\omega+g_{\phi {\rm{B}}}\phi+\dfrac{g_{\rho{\rm{B}}}}{2}\rho\tau_3\right)\right]\psi_{{\rm{B}}} = 0,\\& m_{\sigma}^2\sigma+g_{2}\sigma^2+g_{3}\sigma^3 = \displaystyle \sum\limits_{{\rm{B}}} g_{\sigma{\rm{B}}}\rho^{s}_{{\rm{B}}},\\& m_{\sigma^*}^2\sigma^* = \displaystyle \sum\limits_{{\rm{B}}} g_{\sigma^* {\rm{B}}}\rho^{s}_{{\rm{B}}},\\& m_{\omega}^2\omega+c_{3}\omega^3+2\varLambda_{{\rm{v}}}\left({g^2_{\omega N}}\omega\right)({g^2_{\rho N}}\rho^2) = \displaystyle \sum\limits_{{\rm{B}}} g_{\omega{\rm{B}}}\rho^{v}_{{\rm{B}}},\\& m_{\phi}^2\phi = \displaystyle \sum\limits_{{\rm{B}}} g_{\phi{\rm {B}}}\rho^{v}_{{\rm{B}}},\\& m_{\rho}^2\rho+2\varLambda_{{\rm{v}}}({g^2_{\omega N}}\omega^2)({g^2_{\rho N}}\rho) = \displaystyle \sum\limits_{{\rm{B}}} \dfrac{g_{\rho {\rm{B}}}}{2}\rho^{v3}_{{\rm{B}}}, \end{split}$$ (3) where
$ \tau_3 $ is the isospin third component of the baryon species$ {\rm{B}} $ . The scalar ($ s $ ), vector densities ($ v $ ), and their isospin components are defined as,$$ \begin{array}{l} \rho^s_{{\rm{B}}} = \left\langle\overline{\psi}_{{\rm{B}}}\psi_{{\rm{B}}}\right\rangle,\; \; \; \; \rho^{s3}_{{\rm{B}}} = \left\langle\overline{\psi}_{{\rm{B}}}\tau_3\psi_{{\rm{B}}}\right\rangle,\\ \rho^v_{{\rm{B}}} = \left\langle\psi^{\dagger}_{{\rm{B}}}\psi_{{\rm{B}}}\right\rangle,\; \; \; \; \rho^{v3}_{{\rm{B}}} = \left\langle\psi^{\dagger}_{{\rm{B}}}\tau_3\psi_{{\rm{B}}}\right\rangle. \end{array} $$ (4) The effective masses of baryons in Eq. (3) are dependent on the scalar mesons
$ \sigma $ and$ \sigma^* $ ,$$ M_{{\rm{B}}}^{*} = M_{{\rm{B}}}-g_{\sigma {\rm{B}}}\sigma-g_{\sigma^* {\rm{B}}}\sigma^*. $$ (5) The corresponding effective energies of baryons take the following form because of the mass-energy relation,
$$ E_{{\rm{FB}}}^{*} = \sqrt{k_{{\rm{FB}}}^2+(M_{{\rm{B}}}^{*})^2}, $$ (6) where
$ k_{{\rm{FB}}} $ is the Fermi momentum of baryons.With the energy-momentum tensor in a uniform system, the energy density,
${\cal{E}} $ and pressure,$ P $ of infinite nuclear matter are obtained respectively as[110]$$ \begin{split} {\cal{E}}_{{\rm{NL}}} =& \dfrac{\gamma}{16\pi^2} \displaystyle \sum\limits_{{\rm{B}}} \Bigg[ k_{{\rm{FB}}}E_{{\rm{FB}}}^{*}\left(2k_{{\rm{FB}}}^2 +{M_{{\rm{B}}}^{*}}^2\right) +\\& {M_{{\rm{B}}}^{*}}^4{{\rm{ln}}}\dfrac{M_{{\rm{B}}}^{*}}{k_{{\rm{FB}}}+E_{{\rm{FB}}}^{*}} \Bigg] +\\& \dfrac{1}{2}m_{\sigma}^2\sigma^2+\dfrac{1}{3}g_{2}\sigma^3+\dfrac{1}{4}g_{3}\sigma^4+\dfrac{1}{2}m_{\sigma^*}^2{\sigma^*}^2+\\& \dfrac{1}{2}m_{\omega}^2\omega^2+\dfrac{3}{4}c_{3}\omega^4+\dfrac{1}{2}m_{\rho}^2\rho^2+\\& 3\varLambda_{{\rm{v}}}\left({g^2_{\omega N}}\omega^{2}\right)\left({g^2_{\rho N}}\rho^{2}\right), \end{split} $$ (7) $$ \begin{split} P_{{\rm{NL}}} = & \dfrac{\gamma}{48\pi^2} \displaystyle \sum\limits_{{\rm{B}}}\Bigg[3{M_{{\rm{B}}}^{*}}^{4}{{\rm{ln}}}\dfrac{k_{{\rm{FB}}}+E_{{\rm{FB}}}^{*}}{M_{{\rm{B}}}^{*}} +\\& k_{{\rm{FB}}}^2\left(2k_{{\rm{FB}}}^2-3{M_{{\rm{B}}}^{*}}^2\right)E_{{\rm{FB}}}^{*}\Bigg]- \\& \dfrac{1}{2}m_{\sigma}^2\sigma^2 -\dfrac{1}{3}g_{2}\sigma^3-\dfrac{1}{4}g_{3}\sigma^4-\dfrac{1}{2}m_{\sigma^*}^2{\sigma^*}^2+\\& \dfrac{1}{2}m_{\omega}^2\omega^2+\dfrac{c_{3}}{4}\omega^4+\dfrac{1}{2}m_{\rho}^2\rho^2+\\& \varLambda_{{\rm{v}}}\left({g^2_{\omega N}}\omega^{2}\right)\left({g^2_{\rho N}}\rho^{2}\right), \end{split}$$ (8) where
$ \gamma = 2 $ is the spin degeneracy factor.The outer core part of a neutron star, which almost dominates its mass and radius, is usually treated as the uniform matter consisting of baryons and leptons. Therefore their chemical potentials are very important, that are derived from the thermodynamics equations at zero temperature,
$$ \begin{split} & \mu_{{\rm{B}}} = \sqrt{k_{{\rm{FB}}}^2+M_{{\rm{B}}}^{*2}}+g_{\omega {\rm{B}}}\omega+g_{\phi {\rm{B}}}\phi+\dfrac{g_{\rho {\rm{B}}}}{2}\tau_3\rho,\\ & \mu_l = \sqrt{k_{Fl}^2+m_l^{2}},\; \; \; \; \; l = e,\; \mu. \end{split}$$ (9) -
In the DDRMF model, the Lagrangian density of nuclear many-body system has the similar form as that of NLRMF model,
$$ \begin{split} {\cal{L}}_{{\rm{DD}}} = & \sum\limits_{{\rm{B}}}\overline{\psi}_{{\rm{B}}}\Bigg\{\gamma^{\mu}\bigg[{{\rm{i}}}\partial_{\mu}-\varGamma_{\omega {{\rm{B}}}}(\rho_{{\rm{B}}})\omega_{\mu}-\\& \varGamma_{\phi {{\rm{B}}}}(\rho_{{\rm{B}}})\phi_{\mu}-\dfrac{\varGamma_{\rho {{\rm{B}}}}(\rho_{{\rm{B}}})}{2}{\boldsymbol{\rho}}_{\mu}{\boldsymbol{\tau}}\bigg]-\\ & \bigg[M_{{\rm{B}}}-\varGamma_{\sigma {{\rm{B}}}}(\rho_{{\rm{B}}})\sigma-\varGamma_{\sigma^* {{\rm{B}}}}(\rho_{{\rm{B}}})\sigma^*-\varGamma_{\delta {{\rm{B}}}}(\rho_{{\rm{B}}}){\boldsymbol{\delta}}{\boldsymbol{\tau}}\bigg]\Bigg\}\psi_{{\rm{B}}}+\\& \dfrac{1}{2}\left(\partial^{\mu}\sigma\partial_{\mu}\sigma-m_{\sigma}^2\sigma^2\right) +\dfrac{1}{2}\left(\partial^{\mu}\sigma^*\partial_{\mu}\sigma^*-m_{\sigma^*}^2{\sigma^*}^2\right)+\\ & \dfrac{1}{2}\left(\partial^{\mu}{\boldsymbol{\delta}}\partial_{\mu}{\boldsymbol{\delta}}-m_{\delta}^2{\boldsymbol{\delta}}^2\right) -\dfrac{1}{4}W^{\mu\nu}W_{\mu\nu}+\dfrac{1}{2}m_{\omega}^2\omega_{\mu}\omega^{\mu}-\\& \dfrac{1}{4}\varPhi^{\mu\nu}\varPhi_{\mu\nu}+\dfrac{1}{2}m_{\phi}^2\phi_{\mu}\phi^{\mu} -\dfrac{1}{4}{\boldsymbol{R}}^{\mu\nu}{\boldsymbol{R}}_{\mu\nu}+\dfrac{1}{2}m_{\rho}^2{\boldsymbol{\rho}}_{\mu}{\boldsymbol{\rho}}^{\mu}, \\[-10pt] \end{split}$$ (10) where a scalar-isovector meson (
$ \delta $ ) with mass$ m_{\delta} $ is also introduced due to some parameterization. The coupling constants of$ \sigma $ and$ \omega $ mesons are usually expressed as a fraction function of the total vector density,$\rho^{}_{{\rm{B}}} = \sum\limits_{{\rm{B}}}\rho^v_{{\rm{B}}}$ . In most of DDRMF parametrizations, such as DD2[114], DD-ME1[115], DD-ME2[116], DDME-X[117], PKDD[118], TW99[119], and DDV, DDVT, DDVTD[120], they are assumed as,$$ \varGamma_{iN}(\rho_{{\rm{B}}}) = \varGamma_{iN}(\rho_{{\rm{B}}0})f_i(x) $$ (11) with
$$ f_i(x) = a_i\frac{1+b_i(x+d_i)^2}{1+c_i(x+d_i)^2},\quad x = \rho^{}_{{\rm{B}}}/\rho^{}_{{\rm{B}}0}, $$ (12) for
$ i = \sigma,\; \omega $ .$\rho^{}_{{\rm{B}}0}$ is the saturation density of symmetric nuclear matter from the RMF parameter sets. The couplings$\varGamma_{iN}(\rho^{}_{{\rm{B}}0})$ , and the coefficients$ a_i,\; b_i,\; c_i $ , and$ d_i $ are obtained by fitting the properties of finite nuclei. Five constraints on the coupling constants$f_i(1) = 1, \; f_i^{''}(0) = 0, \; f_{\sigma}^{''}(1) = f_{\omega}^{''}(1)$ can reduce the numbers of independent parameters to three in Eq. (12). The first two constraints lead to$$ a_i = \frac{1+c_i(1+d_i)^2}{1+b_i(1+d_i)^2},\; \; \; \; 3c_id_i^2 = 1. $$ (13) For the isovector mesons
$ \rho $ and$ \delta $ , their density-dependent coupling constants are assumed to be,$$ \varGamma_{iN}(\rho_{{\rm{B}}}) = \varGamma_{iN}(\rho_{{\rm{B}}0}){{\rm{exp}}}[-a_i(x-1)]. $$ (14) While in other parametrizations, such as DD-LZ1[121], the coefficient in front of fraction function,
$ \varGamma_i $ is fixed at$ \rho_{{\rm{B}}} = 0 $ for$ i = \sigma,\; \omega $ :$$ \varGamma_{iN}(\rho_{{\rm{B}}}) = \varGamma_{iN}(0)f_i(x). $$ (15) There are only four constraint conditions as
$ f_i(0) = 1 $ and$ f''_i(0) = 0 $ for$ \sigma $ and$ \omega $ coupling constants in DD-LZ1 set. The constraint$ f''_{\sigma}(1) = f''_{\omega}(1) $ in previous parameter sets was removed in DD-LZ1 parametrization. For$ \rho $ meson, its coupling constant is also changed accordingly as$$ \varGamma_{\rho N}(\rho^{}_{{\rm{B}}}) = \varGamma_{\rho N}(0){{\rm{exp}}}(-a_{\rho}x). $$ (16) Within the mean-field approximation, the meson fields are treated as the classical fields,
$ \left\langle\sigma\right\rangle = \sigma,\; \left\langle\sigma^*\right\rangle = \sigma^*, \; \left\langle\omega_{\mu}\right\rangle = \omega,\; \left\langle\phi_{\mu}\right\rangle = \phi, \; \left\langle{\boldsymbol{\rho}}_{\mu}\right\rangle = \rho,\; \langle\delta\rangle = \delta. $ Together with the Euler-Lagrange equations, the equations of motion for baryons and mesons are given by$$ \begin{split} & \Bigg\{{{\rm{i}}}\gamma^{\mu}\partial_{\mu}-\gamma^0\bigg[\varGamma_{\omega {\rm B}}(\rho_{{\rm{B}}})\omega+\varGamma_{\phi {\rm B}}(\rho_{{\rm{B}}})\phi+\\& \dfrac{\varGamma_{\rho {\rm B}}(\rho_{{\rm{B}}})}{2}\rho\tau_3+\varSigma_R(\rho_{{\rm{B}}})\bigg]-M_{{\rm{B}}}^{*}\Bigg\}\psi_{{\rm{B}}} = 0.\\& m_{\sigma}^2\sigma = \displaystyle \sum\limits_{{\rm{B}}}\varGamma_{\sigma {{\rm{B}}}}(\rho_{{\rm{B}}})\rho^s_{{\rm{B}}},\\& m_{\sigma^*}^2\sigma^* = \displaystyle \sum\limits_{{\rm{B}}}\varGamma_{\sigma^* {\rm{B}}}(\rho_{{\rm{B}}})\rho^s_{{\rm{B}}},\\& m_{\omega}^2\omega = \displaystyle \sum\limits_{{\rm{B}}}\varGamma_{\omega {\rm{B}}}(\rho_{{\rm{B}}})\rho^v_{{\rm{B}}},\\& m_{\phi}^2\phi = \displaystyle \sum\limits_{{\rm{B}}}\varGamma_{\phi {{\rm{B}}}}(\rho_{{\rm{B}}})\rho^v_{{\rm{B}}},\\ & m_{\rho}^2\rho = \displaystyle \sum\limits_{{\rm{B}}}\dfrac{\varGamma_{\rho {\rm{B}}}(\rho_{{\rm{B}}})}{2}\rho^{v3}_{{\rm{B}}},\\& m_{\delta}^2\delta = \displaystyle \sum\limits_{{\rm{B}}}\varGamma_{\delta {\rm{B}}}(\rho_{{\rm{B}}})\rho^{s3}_{{\rm{B}}}. \end{split}$$ (17) Comparing to the NLRMF model, an additional term about the rearrangement contribution,
$ \varSigma_R $ will be introduced into the vector potential in Eq. (17) due to the vector density-dependence of coupling constants,$$ \begin{split} \varSigma_R(\rho^{}_{{\rm{B}}}) = & -\frac{\partial\varGamma_{\sigma {{\rm{B}}}}(\rho^{}_{{\rm{B}}})}{\partial\rho^{}_{{\rm{B}}}}\sigma\rho^s_{{\rm{B}}} -\frac{\partial\varGamma_{\sigma^* {{\rm{B}}}}(\rho^{}_{{\rm{B}}})}{\partial\rho^{}_{{\rm{B}}}}\sigma^*\rho^s_{{\rm{B}}}-\\& \frac{\partial\varGamma_{\delta {{\rm{B}}}}(\rho^{}_{{\rm{B}}})}{\partial\rho^{}_{{\rm{B}}}}\delta\rho^{s3}_{{\rm{B}}} +\frac{1}{2}\frac{\partial\varGamma_{\rho {{\rm{B}}}}(\rho^{}_{{\rm{B}}})}{\partial\rho^{}_{{\rm{B}}}}\rho\rho^{v3}_{{\rm{B}}}+\\& \left[\frac{\partial\varGamma_{\omega {{\rm{B}}}}(\rho^{}_{{\rm{B}}})}{\partial\rho^{}_{{\rm{B}}}}\omega+\frac{\partial\varGamma_{\phi B}(\rho^{}_{{\rm{B}}})}{\partial\rho^{}_{{\rm{B}}}}\phi\right]\rho^v_{{\rm{B}}}, \end{split}$$ (18) where the scalar, vector densities, and their isospin components take the same forms as shown in Eq. (4). The effective masses of baryons in Eq. (17) are dependent on the scalar mesons
$ \sigma $ ,$ \sigma^* $ and$ \delta $ ,$$ M_{{\rm{B}}}^{*} = M_{{\rm{B}}}-\varGamma_{\sigma{{\rm{B}}}}(\rho^{}_{{\rm{B}}})\sigma-\varGamma_{\sigma^* {{\rm{B}}}}(\rho^{}_{{\rm{B}}})\sigma^*-\varGamma_{\delta {{\rm{B}}}}(\rho^{}_{{\rm{B}}})\delta\tau_3 $$ (19) and the corresponding effective energies of baryons take the same form as Eq. (6).
The energy density,
$ {\cal{E}} $ and pressure,$ P $ of nuclear matter in DDRMF model are obtained respectively as$$ \begin{split} {\cal{E}}_{{\rm{DD}}} = & \frac{1}{2}m_{\sigma}^2\sigma^2+\frac{1}{2}m_{\sigma^*}^2{\sigma^*}^2 -\frac{1}{2}m_{\omega}^2\omega^2-\frac{1}{2}m_{\phi}^2\phi^2-\\& \frac{1}{2}m_{\rho}^2\rho^2+\frac{1}{2}m_{\delta}^2\delta^2+\varGamma_{\omega {{\rm{B}}}}(\rho^{}_{{\rm{B}}})\omega\rho_{{\rm{B}}}+\\ & \varGamma_{\phi {{\rm{B}}}}(\rho^{}_{{\rm{B}}})\phi\rho^{}_{{\rm{B}}} +\frac{\varGamma_{\rho}(\rho^{}_{{\rm{B}}})}{2}\rho\rho_3+{\cal{E}}_{{\rm{kin}}}^{{\rm{B}}},\\ P_{{\rm{DD}}} =& \rho^{}_{{\rm{B}}}\varSigma_{R}(\rho^{}_{{\rm{B}}})-\frac{1}{2}m_{\sigma}^2\sigma^2-\frac{1}{2}m_{\sigma^*}^2{\sigma^*}^2+\frac{1}{2}m_{\omega}^2\omega^2+\\& \frac{1}{2}m_{\phi}^2\phi^2+\frac{1}{2}m_{\rho}^2\rho^2- \frac{1}{2}m_{\delta}^2\delta^2+P_{{\rm{kin}}}^{{\rm{B}}}, \end{split}$$ (20) where, the contributions from kinetic energy are
$$ \begin{split} {\cal{E}}_{{\rm{kin}}}^{{\rm{B}}} =& \frac{\gamma}{2\pi^2}\int\nolimits_{0}^{k_{{\rm{FB}}}}k^2\sqrt{k^2+{M_{{\rm{B}}}^{*}}^{2}}{{\rm{d}}}k\\ = & \frac{\gamma}{16\pi^2}\Bigg[k_{{\rm{FB}}}E_{{\rm{FB}}}^{*}\left(2k_{{\rm{FB}}}^2+{M_{{\rm{B}}}^{*}}^2\right)+{M_{{\rm{B}}}^{*}}^4{{\rm{ln}}}\frac{M_{{\rm{B}}}^{*}}{k_{{\rm{FB}}}+E_{{\rm{FB}}}^{*}}\Bigg], \end{split}$$ (21) $$ \begin{split} P_{{\rm{kin}}}^{{\rm{B}}} =& \frac{\gamma}{6\pi^2}\int\nolimits_{0}^{k_{{\rm{FB}}}}\frac{k^4 {\rm d}k}{\sqrt{k^2+{M_{{\rm{B}}}^{*}}^{2}}}\\ =& \frac{\gamma}{48\pi^2}\Bigg[k_{{\rm{FB}}}\left(2k_{{\rm{FB}}}^2-3{M_{{\rm{B}}}^{*}}^2\right)E_{{\rm{FB}}}^{*}+3{M_{{\rm{B}}}^{*}}^{4}{{\rm{ln}}}\frac{k_{{\rm{FB}}}+E_{{\rm{FB}}}^{*}}{M_{{\rm{B}}}^{*}}\Bigg]. \end{split}$$ (22) $ \gamma = 2 $ is the spin degeneracy factor.The chemical potentials of baryons and leptons are
$$ \begin{split} & \mu_{{\rm{B}}} = \sqrt{k_{{\rm{FB}}}^2+M_{{\rm{B}}}^{*2}}+\Big[\varGamma_{\omega {{\rm{B}}}}(\rho_{{\rm{B}}})\omega+\varGamma_{\phi {{\rm{B}}}}(\rho_{{\rm{B}}})\phi+\\& \qquad \frac{\varGamma_{\rho {{\rm{B}}}}(\rho_{{\rm{B}}})}{2}\rho\tau_3+\varSigma_R(\rho_{{\rm{B}}})\Big],\\& \mu_l = \sqrt{k_{{\rm F}l}^2+m_l^{2}}. \end{split}$$ (23) -
In the uniform hyperonic star matter, the compositions of baryons and leptons are determined by the requirements of charge neutrality and
$ \beta $ -equilibrium conditions. All baryon octets$ (n,\; p,\; \varLambda,\; \varSigma^-,\; \varSigma^0,\; \varSigma^+,\; \varXi^-,\; \varXi^0) $ and leptons ($ e,\; \mu $ ) will be included in this work. The$ \beta $ -equilibrium conditions can be expressed by[61, 75]$$ \begin{array}{*{20}{c}} {\mu_p = \mu_{\varSigma^+} = \mu_n-\mu_e,}\\ {\mu_{\varLambda} = \mu_{\varSigma^0} = \mu_{\varXi^0} = \mu_n,}\\ {\mu_{\varSigma^-} = \mu_{\varXi^-} = \mu_n+\mu_e,}\\ {\mu_{\mu} = \mu_e, } \end{array}$$ (24) where
$ \mu_i $ has defined in Eqs. (9) and (23). The charge neutrality condition has the following form,$$ \rho^v_{p}+\rho^v_{\varSigma^+} = \rho^v_e+\rho^v_{\mu}+\rho^v_{\varSigma^-}+\rho^v_{\varXi^-}. $$ (25) The total energy density and pressure of neutron star matter will be obtained as a function of baryon density within the constraints of Eqs. (24) and (25). The Tolman-Oppenheimer-Volkoff (TOV) equation describes a spherically symmetric star in the gravitational equilibrium from general relativity[122-123],
$$ \begin{split} & \frac{{{\rm{d}}}P}{{{\rm{d}}}r} = -\frac{GM(r){\cal{E}}(r)}{r^2}\frac{\left[1+\frac{P(r)}{{\cal{E}}(r)}\right]\left[1+\frac{4\pi r^3P(r)}{M(r)}\right]}{1-\frac{2GM(r)}{r}},\\ & \frac{{{\rm{d}}}M(r)}{{{\rm{d}}}r} = 4\pi r^2{\cal{E}}(r), \end{split} $$ (26) where P and M are the pressure and mass of a neutron star at the position
$ r $ and G is the gravitational constant. Furthermore, the tidal deformability becomes a typical property of a neutron star after the observation of the gravitational wave from a binary neutron-star (BNS) merger, which characterizes the deformation of a compact object in an external gravity field generated by another star. The tidal deformability of a neutron star is reduced as a dimensionless form[124-125],$$ \varLambda = \frac{2}{3}k_2C^{-5}, $$ (27) where
$ C = GM/R $ is the compactness parameter. The second order Love number$ k_2 $ is given by$$ \begin{split} k_2 =& \dfrac{8C^5}{5}(1-2C)^2\left[2+2C({\cal{Y}}_R-1)-{\cal{Y}}_R\right]\times\\& \Big\{2C\big[6-3{\cal{Y}}_R+3C(5{\cal{Y}}_R-8)\big]+\\& 4C^3\left[13-11{\cal{Y}}_R+C(3{\cal{Y}}_R-2)+2C^2(1+{\cal{Y}}_R)\right]+\\& 3(1-2C)^2\left[2-{\cal{Y}}_R+2C({\cal{Y}}_R-1){{\rm{ln}}}(1-2C)\right]\Big\}^{-1}. \end{split}$$ (28) Here,
$ {\cal{Y}}_R = y(R) $ .$ y(r) $ satisfies the following first-order differential equation,$$ r\frac{{{\rm{d}}} y(r)}{{{\rm{d}}}r} + y^2(r)+y(r)F(r) + r^2Q(r) = 0, $$ (29) where
$ F(r) $ and$ Q(r) $ are functions related to the pressure and energy density$$ \begin{split} F(r) =& \left[1-\frac{2M(r)}{r}\right]^{-1} \bigg\{1-4\pi r^2\Big[{\cal{E}}(r)-P(r)\Big]\bigg\} ,\\ r^2Q(r) = &\left\{4\pi r^2 \left[5{\cal{E}}(r)+9P(r)+\frac{{\cal{E}}(r) +P(r)}{\frac{\partial P}{\partial {\cal{E}}}(r)}\right]-6\right\}\times\\ & \left[1-\frac{2M(r)}{r}\right]^{-1} -\left[\frac{2M(r)}{r} +2\times4\pi r^2 P(r) \right]^2\times\\& \left[1-\frac{2M(r)}{r}\right]^{-2} . \end{split} $$ (30) The second Love number corresponds to the initial condition
$ y(0) = 2 $ . It is also related to the speed of sound in compact matter,$ c_{\rm s} $ ,$$ c_s^2 = \frac{\partial P(\varepsilon)}{\partial{{\cal{E}}}}. $$ (31) -
In the present work, four popular parameter sets, TM1[103], NL3[126], IUFSU[113], and BigApple[127] in the NLRMF model are used to describe the uniform matter, which was generated by fitting the ground state properties of several stable nuclei. The nonlinear term of the vector meson was considered in the TM1 set to reproduce the nucleon vector potential from the RBHF model. The NL3 set can generate a large maximum mass of a neutron star, while its radius is large[58]. The
$ \omega $ -$ \rho $ meson coupling term was included in the IUFSU set. The BigApple set can lead to a large maximum mass of a neutron star with a small radius due to the smaller slope of the symmetry energy[127]. The masses of nucleons and mesons, and the coupling constants between nucleon and mesons in NLRMF models, TM1[103], IUFSU[113], BigApple[127], NL3[126] are tabulated in Table 1.Table 1. Masses of nucleons and mesons, meson coupling constants in various NLRMF models.
Parameter NL3[126] BigApple[127] TM1[103] IUFSU[113] $m_n$/MeV 939.000 0 939.000 0 938.000 0 939.000 0 $m_p$/MeV 939.000 0 939.000 0 938.000 0 939.000 0 $m_{\sigma}$/MeV 508.194 0 492.730 0 511.198 0 491.500 0 $m_{\omega}$/MeV 782.501 0 782.500 0 783.000 0 782.500 0 $m_{\rho}$/MeV 763.000 0 763.000 0 770.000 0 763.000 0 $g_{\sigma}$ 10.217 0 9.669 9 10.028 9 9.971 3 $g_{\omega}$ 12.868 0 12.316 0 12.613 9 13.032 1 $g_{\rho}$ 8.948 0 14.161 8 9.264 4 13.589 9 $g_2/\rm fm^{-1}$ 10.431 0 11.921 4 7.232 5 8.492 9 $g_3$ −28.885 0 −31.679 6 0.618 3 0.487 7 $c_3$ 0.000 0 2.684 3 71.307 5 144.219 5 $\varLambda_V$ 0.000 0 0.047 5 0.000 0 0.046 0 For the DDRMF models, the parametrizations, DD2[114], DD-ME1[115], DD-ME2[116], DDME-X[116], PKDD[118], TW99[119], DDV, DDVT, DDVTD[120], and DD-LZ1[121] are listed in Table 2. TW99, DD2, DD-ME1, DD-ME2, and PKDD parameter sets were obtained by reproducing the ground-state properties of different nuclei before 2005. In recent years, the DDME-X, DD-LZ1, DDV, DDVT, and DDVTD sets were brought out with various considerations. In DDVT and DDVTD sets, the tensor coupling between the vector meson and nucleon was included. The scalar-isovector meson,
$ \delta $ was taken into account in DDVTD. The coefficients of meson coupling constants,$ \varGamma_i $ in DD-LZ1 are the values at zero density, while other parameter sets are dependent on the values at nuclear saturation densities.Table 2. Masses of nucleons and mesons, meson coupling constants, and the nuclear saturation densities in various DDRMF models.
Parameter DD-LZ1[121] DD-MEX[117] DD-ME2[116] DD-ME1[115] DD2[114] PKDD[118] TW99[119] DDV[120] DDVT[120] DDVTD[120] $m_n$/MeV 938.9000 939.0000 939.0000 939.0000 939.5654 939.5731 939.0000 939.5654 939.5654 939.5654 $m_p$/MeV 938.9000 939.0000 939.0000 939.0000 938.2720 938.2796 939.0000 938.2721 938.2721 938.2721 $m_{\sigma}$/MeV 538.6192 547.3327 550.1238 549.5255 546.2125 555.5112 550.0000 537.6001 502.5986 502.6198 $m_{\omega}$/MeV 783.0000 783.0000 783.0000 783.0000 783.0000 783.0000 783.0000 783.0000 783.0000 783.0000 $m_{\rho}$/MeV 769.0000 763.0000 763.0000 763.0000 763.0000 763.0000 763.0000 763.0000 763.0000 763.0000 $m_{\delta}$/MeV — — — — — — — — — 980.0000 $\varGamma_{\sigma}(0)$ 12.0014 — — — — — — — — — $\varGamma_{\omega}(0)$ 14.2925 — — — — — — — — — $\varGamma_{\rho}(0)$ 15.1509 — — — — — — — — — $\varGamma_{\delta}(0)$ — — — — — — — — — — $\varGamma_{\sigma}(\rho_{{\rm{B}}0})$ — 10.7067 10.5396 10.4434 10.6867 10.7385 10.7285 10.1370 8.3829 8.3793 $\varGamma_{\omega}(\rho_{{\rm{B}}0})$ — 13.3388 13.0189 12.8939 13.3424 13.1476 13.2902 12.7705 10.9871 10.9804 $\varGamma_{\rho}(\rho_{{\rm{B}}0})$ — 7.2380 7.3672 7.6106 7.2539 8.5996 7.3220 7.8483 7.6971 8.0604 $\varGamma_{\delta}(\rho_{{\rm{B}}0})$ — — — — — — — — — 0.8487 $\rho_{{\rm{B}}0}/{\rm{fm}}^{-3}$ 0.1581 0.1520 0.1520 0.1520 0.1490 0.1496 0.1530 0.1511 0.1536 0.1536 $a_{\sigma}$ 1.0627 1.3970 1.3881 1.3854 1.3576 1.3274 1.3655 1.2100 1.2040 1.1964 $b_{\sigma}$ 1.7636 1.3350 1.0943 0.9781 0.6344 0.4351 0.2261 0.2129 0.1921 0.1917 $c_{\sigma}$ 2.3089 2.0671 1.7057 1.5342 1.0054 0.6917 0.4097 0.3080 0.2777 0.2738 $d_{\sigma}$ 0.3800 0.4016 0.4421 0.4661 0.5758 0.6942 0.9020 1.0403 1.0955 1.1034 $a_{\omega}$ 1.0592 1.3936 1.3892 1.3879 1.3697 1.3422 1.4025 1.2375 1.1608 1.1669 $b_{\omega}$ 0.4183 1.0191 0.9240 0.8525 0.4965 0.3712 0.1726 0.0391 0.0446 0.0264 $c_{\omega}$ 0.5387 1.6060 1.4620 1.3566 0.8178 0.6114 0.3443 0.0724 0.0672 0.0423 $d_{\omega}$ 0.7866 0.4556 0.4775 0.4957 0.6385 0.7384 0.9840 2.1457 2.2269 2.8062 $a_{\rho}$ 0.7761 0.6202 0.5647 0.5008 0.5189 0.1833 0.5150 0.3527 0.5487 0.5580 $a_{\delta}$ — — — — — — — — — 0.5580 The saturation properties of symmetric nuclear matter calculated with different RMF effective interactions are listed in Table 3,
$ i.e $ . the saturation density,$ \rho_0 $ , the binding energy per nucleon,$ E/A $ , incompressibility,$ K_0 $ , symmetry energy,$ E_\text{sym} $ , the slope of symmetry energy,$ L $ , and the effective neutron and proton masses,$ M^*_{\rm n} $ and$ M^*_{\rm p} $ . The saturation densities of nuclear matter are in the region of$0.145 \sim 0.158$ fm−3. The binding energies per nucleon at saturation density are around$ -16.5 $ MeV. The incompressibilities of nuclear matter are$230 \sim 280$ MeV. The symmetry energies are$31 \sim 37$ MeV. The slopes of the symmetry energy from these RMF interactions have large uncertainties, from$40 \sim 120$ MeV, since there are still not too many experimental constraints about the neutron skin[128-133]. The effective mass differences between neutron and proton in this table are caused by the differences of their free masses.Table 3. Nuclear matter properties at saturation density generated by NLRMF and DDRMF parameterizations.
Model $\rho_{{\rm{B}}0}/{\rm{fm}}^{-3}$ $E/A$/MeV $K_0$/MeV $E_{{\rm{sym}}}$/MeV $L_0$/MeV $M_{\rm n}^{*}/M$ $M_{\rm p}^{*}/M$ NL3 0.1480 −16.2403 269.9605 37.3449 118.3225 0.5956 0.5956 BigApple 0.1545 −16.3436 226.2862 31.3039 39.7407 0.6103 0.6103 TM1 0.1450 −16.2631 279.5858 36.8357 110.6082 0.6348 0.6348 IUFSU 0.1545 −16.3973 230.7491 31.2851 47.1651 0.6095 0.6095 DD-LZ1 0.1581 −16.0598 231.1030 31.3806 42.4660 0.5581 0.5581 DD-MEX 0.1519 −16.0973 267.3819 32.2238 46.6998 0.5554 0.5554 DD-ME2 0.1520 −16.1418 251.3062 32.3094 51.2653 0.5718 0.5718 DD-ME1 0.1522 −16.2328 245.6657 33.0899 55.4634 0.5776 0.5776 DD2 0.1491 −16.6679 242.8509 31.6504 54.9529 0.5627 0.5614 DD2 0.1495 −16.9145 261.7912 36.7605 90.1204 0.5713 0.5699 TW99 0.1530 −16.2472 240.2022 32.7651 55.3095 0.5549 0.5549 DDV 0.1511 −16.9279 239.9522 33.5969 69.6813 0.5869 0.5852 DDVT 0.1536 −16.9155 239.9989 31.5585 42.3414 0.6670 0.6657 DDVTD 0.1536 −16.9165 239.9137 31.8168 42.5829 0.6673 0.6660 For the hyperonic star matter with strangeness degree of freedom, the hyperon masses are chosen as
$ m_{\varLambda} = 1~115.68 $ MeV,$ m_{\varSigma^+} = 1~189.37 $ MeV,$ m_{\varSigma^0} = 1~192.64 $ MeV,$ m_{\varSigma^-} = 1~197.45 $ MeV,$ m_{\varXi^0} = 1~314.86 $ MeV, and$ m_{\varXi^-} = 1~321.71 $ MeV[134], while the masses of strange mesons,$ \phi $ and$ \sigma^* $ are taken as$ m_{\phi} = 1~020 $ MeV and$ m_{\phi} = 980 $ MeV. We adopt the values from the SU(6) symmetry for the coupling constants between hyperons and vector mesons[135] both in NLRMF and DDRMF models. Here, the coupling constants of the DDRMF model are taken as an example,$$ \begin{array}{*{20}{c}} {\varGamma_{\omega\varLambda} = \varGamma_{\omega\varSigma} = 2\varGamma_{\omega\varXi} = \frac{2}{3}\varGamma_{\omega N},}\\ {2\varGamma_{\phi\varSigma} = \varGamma_{\phi\varXi} = -\frac{2\sqrt{2}}{3}\varGamma_{\omega N},\quad \varGamma_{\phi N} = 0,}\\ {\varGamma_{\rho\varLambda} = 0,\quad \varGamma_{\rho\varSigma} = 2\varGamma_{\rho\varXi} = 2\varGamma_{\rho N},}\\ {\varGamma_{\delta\varLambda} = 0,\quad \varGamma_{\delta\varSigma} = 2\varGamma_{\delta\varXi} = 2\varGamma_{\delta N}, } \end{array}$$ (32) where
$ \varGamma_{iN} $ has been defined in Eq. (14)~Eq. (16) for DDRMF models. The coupling constants of hyperon and scalar mesons are constrained by the hyperon-nucleon potentials in symmetric nuclear matter,$ U_Y^N $ , which are defined by$$ \begin{split} U_Y^N(\rho_{{{\rm{B}}}0}) = -R_{\sigma Y}\varGamma_{\sigma N}(\rho_{{{\rm{B}}}0})\sigma_0+R_{\omega Y}\varGamma_{\omega N}(\rho_{{{\rm{B}}}0})\omega_0, \end{split} $$ (33) where
$ \varGamma_{\sigma N}(\rho_{{{\rm{B}}}0}),\; \varGamma_{\omega N}(\rho_{{{\rm{B}}}0}),\; \sigma_0,\; \omega_0 $ are the values of coupling strengths and$ \sigma,\; \omega $ meson fields at the saturation density.$ R_{\sigma Y} $ and$ R_{\omega Y} $ are defined as$ R_{\sigma Y} = \varGamma_{\sigma Y}/\varGamma_{\sigma N} $ and$ R_{\omega Y} = \varGamma_{\omega Y}/\varGamma_{\omega N} $ . We choose the hyperon-nucleon potentials of$ \varLambda,\; \varSigma $ and$ \varXi $ as$ U_{\varLambda}^N = -30 $ MeV,$ U_{\varSigma}^N = +30 $ MeV and$ U_{\varXi}^N = -14 $ MeV, respectively from the recent hypernuclei experimental observables[72, 81, 136].The coupling constants between
$ \varLambda $ and$ \sigma^* $ is generated by the value of the$ \varLambda\varLambda $ potential in pure$ \varLambda $ matter,$ U_{\varLambda}^{\varLambda} $ at nuclear saturation density, which is given as$$ \begin{split} U_{\varLambda}^{\varLambda}(\rho_{{{\rm{B}}}0}) =& -R_{\sigma\varLambda}\varGamma_{\sigma N}(\rho_{{{\rm{B}}}0})\sigma_0-R_{\sigma^*\varLambda}\varGamma_{\sigma N}(\rho_{{{\rm{B}}}0}){\sigma^*_0}+\\& R_{\omega Y}\varGamma_{\omega N}(\rho_{{{\rm{B}}}0})\omega_0+R_{\phi\varLambda}\varGamma_{\omega N}(\rho_{{{\rm{B}}}0})\phi_0. \end{split}$$ (34) We similarly define that
$ R_{\sigma^*\varLambda} = \varGamma_{\sigma^*\varLambda}/\varGamma_{\sigma N} $ and$ R_{\phi\varLambda} = \varGamma_{\phi\varLambda}/ \varGamma_{\omega N} $ .$ R_{\sigma^*\varLambda} $ is obtained from the$ \varLambda-\varLambda $ potential as$ U_{\varLambda}^{\varLambda}(\rho_{{{\rm{B}}}0}) = -10 $ MeV, which was extracted from the$ \varLambda $ bonding energies of double-$ \varLambda $ hypernuclei.$ R_{\phi\varLambda} = -\sqrt{2}/2 $ is corresponding to the SU(6) symmetry broken case[81]. Here, the coupling between the$ \varSigma $ ,$ \varXi $ hyperons and$ \sigma^* $ mesons are set as$ R_{\sigma^*\varXi} = 0,\; R_{\sigma^*\varSigma} = 0 $ , since the information about their interaction is absent until now. The values of$ R_{\sigma Y} $ and$ R_{\sigma^*\varLambda} $ with above constraints in different RMF effective interactions are shown in Table 4.Table 4. The Coupling constants between hyperons and
$\sigma$ meson,$g_{\sigma Y}$ and$\varLambda$ -$\sigma^*$ ,$g_{\sigma^*\varLambda}$ in different RMF effective interactions.Model $R_{\sigma\varLambda}$ $R_{\sigma\varSigma}$ $R_{\sigma\varXi}$ $R_{\sigma^*\varLambda}$ NL3 0.6189 0.4609 0.3068 0.8470 BigApple 0.6163 0.4528 0.3054 0.8631 TM1 0.6211 0.4459 0.3076 0.8371 IUFSU 0.6162 0.4530 0.3054 0.8880 DD-LZ1 0.6104 0.4657 0.3028 0.8760 DD-MEX 0.6128 0.4692 0.3040 0.8623 DD-ME2 0.6099 0.4607 0.3025 0.8576 DD-ME1 0.6086 0.4572 0.3018 0.8583 DD2 0.6127 0.4666 0.3039 0.8642 PKDD 0.6104 0.4618 0.3027 0.8497 TW99 0.6120 0.4688 0.3036 0.8582 DDV 0.6074 0.4528 0.3011 0.8798 DDVT 0.5912 0.3993 0.2924 0.9226 DDVTD 0.5911 0.3990 0.2924 0.9225 -
With the conditions of
$ \beta $ equilibrium and charge neutrality, the equations of state (EoSs) of neutron star matter including the neutron, proton, and leptons, i.e. the$ P-\epsilon $ function in the NLRMF and DDRMF models is obtained in the panel (a) and panel (b) of Fig. 1, which shows the pressures of neutron star matter as a function of energy density. For the inner crust part of a neutron star, the EoS of the non-uniform matter generated by TM1 parametrization with self-consistent Thomas-Fermi approximation is adopted[38]. In the core region of a neutron star, the EoSs of the uniform matter are calculated with various NLRMF and DDRMF parameter sets. Furthermore, the joint constraints on the EoS extracted from the GW170817 and GW190814 are shown as a shaded band[21], which was obtained from the gravitational wave signal by Bayesian method with the spectral EoS parametrizations[18]. The pressures from TM1 and NL3 sets around saturation density are larger than those from IUFSU and BigApple sets since their incompressibilities$ K_0 $ are about$270 \sim 280$ MeV. At the high-density region, the EoSs from NL3 and BigApple become stiffer since$ g_3 $ in these two sets are negative, which will produce smaller scalar fields and provide less attractive contributions to the EoSs. In DDRMF parameter sets, the EoSs have similar density-dependent behaviors. The DDV, DDVT, DDVTD, and TW99 sets generate the softer EoSs compared to other sets.Figure 1. (color online) The pressure
$P$ versus energy density$\varepsilon$ of neutron star matter and hyperonic star matter from NLRMF and DDRMF models. The joint constraints on EoS extracted from the GW170817 and GW190814 are shown as a shaded green band. Panels (a) and panel (b) for the neutrons star matter from the NLRMF and DDRMF models, respectively. Panels (c) and panel (d) for the hyperonic star matter from the NLRMF and DDRMF models, respectively.After considering more conditions of beta equilibrium and charge neutrality about the hyperons, the EoSs of hyperonic star matter from the NLRMF and DDRMF models, where the coupling strengths between the mesons and hyperons are described as before, can be obtained in panel (c) and panel (d) of Fig. 1. They almost become softer from
$\varepsilon \sim 300$ MeV/fm3 compared to the neutron star matter, due to the appearances of hyperons. In high-density region, all of them are below the joint constraints on the EoS from GW170817 and GW190814 events.Similarly, in panel (a) and panel (b) of Fig. 2, the pressures as functions of baryon density in neutron star matter from NLRMF and DDRMF models are given. Furthermore, the speeds of sound in neutron star matter,
$ c_s $ , which has been defined in Eq. (31) with the unit of light speed are plotted in the insert. Since the NLRMF and DDRMF models are constructed based on the relativistic theory, the speeds of the sound from the RMF framework should be less than 1 due to the causality. The NL3 set brings out the largest speed of the sound, while the$ c^2_{\rm s}/c^2 $ from TM1 and IUFSU sets at high density approach 0.4. It is noteworthy that$ c^2_{\rm s}/c^2 $ is 1/3 from the conformal limit of quark matter[54, 56].Figure 2. (color online) EoSs of neutron star and hyperonic star matter with different NLRMF and DDRMF models. The corresponding speeds of sound in units of the speed of light shown in the insert. Panels (a) and panel (b) for the neutrons star matter from the NLRMF and DDRMF models, respectively. Panels (c) and panel (d) for the hyperonic star matter from the NLRMF and DDRMF models, respectively.
The pressures as functions of density in hyperonic star matter from NLRMF and DDRMF models are given in panel (c) and panel (d), respectively. The onset densities of the first hyperon are marked by the full discretized symbols, which are around
$0.28 \sim 0.45$ fm−3. The speed of sound of hyperonic star matter is not smooth as a function density anymore. The appearance of hyperon can sharply reduce the magnitude of the speed of sound, especially at first onset density. For the hard EoS, the$ c^2_{\rm s} $ becomes$ 0.6 $ in hyperonic star matter from$ 0.8 $ in neutron star matter at high-density region.The onset densities of
$ \varLambda,\; \varSigma $ , and$ \varXi $ hyperons in various NLRMF and DDRMF models are listed in Table 5. In general, the$ \varLambda $ hyperon firstly arises around$2 \sim 3\rho_0$ due to its small mass and large attractive$ \varLambda N $ potential. The most probable baryon of the second onset is the$ \varSigma^- $ hyperon for$\rho_{{\rm{B}}} < 4\rho_0$ , whose mass is very close to that of the$ \varLambda $ hyperon. In a few parameter sets, such as NL3, PKDD, DDVT, and DDVTD, the second appearing hyperon is the$ \varXi^- $ hyperon, which can bind with the nucleons to form the$ \varXi^- $ hypernuclei. With the density increasing, the$ \varXi^- $ hyperon usually emerges above$ 4\rho_0 $ and$ \varXi^0 $ appears above$ 7\rho_0 $ .Table 5. Hyperon thresholds calculated with different RMF effective interactions for hyperonic matter. The unit of the density is fm−3.
Model $ 1^{{\rm{st}}}$ ($\rho_{\rm{th}}$) $ 2^{{\rm{nd}}}$ ($\rho_{\rm{th}}$) $ 3^{{\rm{rd}}}$ ($\rho_{\rm{th}}$) $ 4^{{\rm{th}}}$ ($\rho_{\rm{th}}$) NL3 $\varLambda$ (0.2804) $\varXi^-$ (0.6078) $\varXi^0$ (0.9723) $\varSigma^-$(1.3545) BigApple $\varLambda$ (0.3310) $\varSigma^-$ (0.4895) $\varXi^-$ (0.6191) $\varXi^0$ (1.2758) TM1 $\varLambda$ (0.3146) $\varSigma^-$ (0.9995) $\varXi^-$ (1.0228) IUFSU $\varLambda$ (0.3800) $\varSigma^-$ (0.5645) DD-LZ1 $\varLambda$ (0.3294) $\varSigma^-$ (0.4034) $\varXi^-$ (0.6106) $\varXi^0$ (1.2935) DD-MEX $\varLambda$ (0.3264) $\varSigma^-$ (0.3871) $\varXi^-$ (0.5967) $\varXi^0$ (1.2699) DD-ME2 $\varLambda$ (0.3402) $\varSigma^-$ (0.4244) $\varXi^-$ (0.4895) $\varXi^0$ (1.3237) DD-ME1 $\varLambda$ (0.3466) $\varSigma^-$ (0.4424) $\varXi^-$ (0.4740) $\varXi^0$ (1.3545) DD2 $\varLambda$ (0.3387) $\varSigma^-$ (0.4147) $\varXi^-$ (0.5699) $\varXi^0$ (1.3733) PKDD $\varLambda$ (0.3264) $\varXi^-$ (0.4016) $\varSigma^-$ (0.5126) $\varXi^0$ (1.0759) TW99 $\varLambda$ (0.3696) $\varSigma^-$ (0.4167) $\varXi^-$ (0.7109) $\varXi^0$ (1.7052) DDV $\varLambda$ (0.3547) $\varSigma^-$ (0.4850) $\varXi^-$ (0.7723) DDVT $\varLambda$ (0.4465) $\varXi^-$ (0.4941) $\varSigma^-$ (0.6220) DDVTD $\varLambda$ (0.4465) $\varXi^-$ (0.4963) $\varSigma^-$ (0.6163) The corresponding particle fractions of baryons as a function of baryon number density with different NLRMF and DDRMF parameter sets are shown in Fig. 3 and Fig. 4, respectively. At a low-density region, the hyperonic matter is almost consisting of neutrons. The proton and electron fractions rapidly increase with density. When the chemical potential of the electron is larger than the free muon mass, the muon will arise. Above
$ 2\rho_0 $ , the various hyperons appear in the hyperonic matter when they satisfy the chemical equilibrium conditions. At the high-density region, the fractions of various particles are strongly dependent on the NN and NY interactions. However, at all events, the fractions of$ \varLambda $ hyperon will approach that of neutrons. In some cases, it can exceed those of neutrons.Figure 3. (color online) Particle fractions of baryons as a function of baryon number density with different NLRMF parameter sets.
Figure 4. (color online) Particle fractions of baryons as a function of baryon number density with different DDRMF parameter sets.
After solving the TOV equation, the mass-radius relation of a static neutron star is obtained, where the EoSs of neutron star matter in the previous part are used. In Fig. 5, the mass-radius (
$ M-R $ ) relations from NLRMF sets and DDRMF sets are shown in panel (a) and panel (b), respectively. The constraints from the observables of massive neutron stars, PSR J1614-2230 and PSR J034+0432 are also shown as the shaded bands. In 2019, the Neutron star Interior Composition Explorer (NICER) collaboration reported an accurate measurement of mass and radius of PSR J0030+0451, simultaneously. It may be a mass of$1.44_{-0.14}^{+0.15}~M_\odot$ with a radius of$ 13.02_{-1.06}^{+1.24} $ km[137] and a mass of$1.34_{-0.16}^{+0.15}~M_\odot$ with a radius of$ 12.71_{-1.19}^{+1.14} $ km[138] by two independent analysis groups. Recently, the radius of the pulsar PSR J0740+6620 with mass was reported by two independent groups based on NICER and X-ray Multi-Mirror (XMM-Newton) observations. The inferred radius of this massive NS is constrained to$ 12.39_{-0.98}^{+1.30} $ km for the mass$2.072^{+0.006~7}_{-0.066}~M_{\odot}$ by Riley$ et\; al. $ [139] and$ 13.7_{-1.5}^{+2.6} $ km for the mass$2.08\pm0.07~M_\odot$ by Miller$ et\; al. $ at 68% credible level[16]. These constraints from NICER analyzed by Riley et al. are plotted in Fig. 5. Meanwhile, the radius at$1.4~M_{\odot}$ extracted from GW170817 is also shown[18].Figure 5. (color online) The neutron and hyperonic star masses as functions of radius for NLRMF and DDRMF sets. Constraints from astronomical observables for the massive neutron star, NICER, and GW170817 are also shown. Panels (a) and panel (b) for the neutrons star matter from the NLRMF and DDRMF models, respectively. Panels (c) and panel (d) for the hyperonic star matter from the NLRMF and DDRMF models, respectively.
Among all parameter set used, NL3 predicts the heaviest neutron star mass (
$2.77~M_\odot$ ) due to its hard EoS, while the corresponding radius at$1.4~M_\odot$ does not satisfy the measurements from GW170817 and NICER. It can be found that the radii at$1.4~M_\odot$ from NL3 and TM1 sets are much larger than those from other RMF sets. This is caused by their large slope of symmetry energy,$ L = 110.6 $ MeV from TM1 and$ L = 118.3 $ MeV from NL3. In our previous works[140-141], the extended TM1 and IUFSU parameter sets, which can generate different$ L $ and keep the isoscalar properties of nuclear many-body systems, were applied to systematically study the symmetry energy effect on the neutron star. We found that there is a strong correlation between the$ L $ and the radius of the neutron star at$1.4~M_\odot$ , while its influence on the maximum mass of the neutron star is very small. Furthermore, the tidal deformability, which is related to the radius of neutron also provides the constraints to$ L $ . From the present astrophysical observables, the slope of symmetry energy should be less than 80 MeV. On the other hand,$ L $ is also related to the neutron skin of the neutron-rich nuclei, such as$ ^{208}\rm{Pb} $ . However, recent experimental data about the neutron skin of$ ^{208}\rm{Pb} $ from PREXII prefers the larger$ L $ [142-144]. This contradiction should be discussed in detail in the future. The softer EoSs from IUFSU, DDV, DDVT, and DDVTD cannot generate the$2~M_\odot$ neutron stars and the radii at$ 1.4~M_\odot $ from them are smaller compared to the other sets. BigApple, DD-LZ1, and DD-MEX sets can produce the neutron star heavier than$ 2.5~M_\odot $ , whose radii at$ 1.4~M_\odot $ also accords with the constraints from gravitational wave and NICER. Therefore, we cannot exclude the possibility of the secondary in GW190814 as a neutron star[145]. For the massive neutron stars above$ 2~M_\odot $ , from the stiffer EoSs, their central densities are less than$ 0.9 $ fm−3, while the softer EoSs may reach the central densities larger than$ 0.9 $ fm−3 for the lighter neutron stars.The mass-radius (
$ M-R $ ) relations of hyperonic star from NLRMF and DDRMF parameter sets are shown in panel (c) and panel (d) of Fig. 5, respectively. The onset positions of the first hyperon in the relations are shown as the discretized symbols. After considering the strangeness degree of freedom, the maximum masses of the hyperonic star will reduce about$15{\text%} \sim 20{\text \%}$ . In the NLRMF model, only the NL3 and BigApple parameter sets can support the existence of$2~M_\odot$ compact star with hyperons, while in the DDRMF model, the DD-LZ1, DD-MEX, DD-ME2, DD-ME1, DD2, and PKDD sets generate the hyperonic star heavier than$ 2~M_\odot $ . Furthermore, the central densities of the hyperonic star become higher compared to the neutron star, all of which are above$ 5\rho_0 $ . The role of hyperons in the lower mass hyperonic star is strongly dependent on the threshold density of the first onset hyperon. The properties of a hyperonic star whose central density is below this threshold are identical to those of a neutron star. When the central density of the hyperonic star is larger than the threshold, the properties of hyperonic star will be influenced. For the softer EoSs, the lower mass neutron stars are more easily affected, because their central densities are much larger than those generated by the harder EoSs at the same neutron star mass. For example, the radii of the hyperonic stars at$ 1.4~M_\odot $ from DDV, DDVT, and DDVTD decrease about$5{\text%}$ compared to those of the neutron stars.In Fig. 6, the dimensionless tidal deformability,
$ \varLambda $ , of neutron stars as a function of their masses from different NLRMF and DDRMF models are shown in panel (a) and panel (b), respectively. The tidal deformability represents the quadrupole deformation of a compact star in the external gravity field generated by its companion star, which is related to the mass, radius, and Love number of the star. From the gravitation wave of BNS merger in GW170817, it was extracted as$ \varLambda_{1.4} = 190^{+390}_{-120} $ at$1.4~M_\odot$ [18]. It is found that the$ \varLambda_{1.4} $ worked out by NLRMF models are larger than the constraint of GW170817 since their radii are greater than 12 km. For the massive neutron star, its tidal deformability is very small and close to 1. The$ \varLambda_{1.4} $ from DDRMF models is separated into two types. The first type with the stiffer EoSs has the larger$ \varLambda_{1.4} $ and heavier masses, whose$ \varLambda_{1.4} $ are out the constraint of GW170817. The second one completely satisfies the constraints of GW170817 and has smaller radii from the softer EoSs. It was also shown the tidal deformability of the neutron star at$2.0~M_\odot$ , which is expected to be measured in the future gravitational wave events from the binary neutron-star merger.Figure 6. (color online) The dimensionless tidal deformability as a function of star mass for NLRMF and DDRMF sets. The constraints from GW170817 event for tidal deformability is shown. Panels (a) and panel (b) for the neutrons star matter from the NLRMF and DDRMF models, respectively. Panels (c) and panel (d) for the hyperonic star matter from the NLRMF and DDRMF models, respectively.
The dimensionless tidal deformabilities of hyperonic star are plotted in the panel (c) and panel (d) of Fig. 6. For the harder EoSs, the hyperons only can influence the magnitudes of
$ \varLambda $ at the maximum star mass region, while they can reduce the dimensionless tidal deformability at$1.4~M_\odot$ for the softer EoSs, such as TW99, DDV, DDVT, and DDVTD set, whose$ \varLambda_{1.4} $ are closer to the constraints from GW170817. Therefore, the compact stars in the GW170817 events may be the hyperonic stars.Finally, the properties of neutron star and hyperonic star, i.e., the maximum mass (
$ M_{{\rm{max}}}/M_{\odot} $ ), the corresponding radius ($ R_{{\rm{max}}} $ ), the central density ($ \rho_c $ ), the radius ($ R_{1.4} $ ) and dimensionless tidal deformability ($ \varLambda_{1.4} $ ) at$1.4~M_\odot$ from present NLRMF and DDRMF models are listed in Table 6. The maximum masses of neutron stars from these models are around$1.85\sim2.77~M_\odot$ , whose radii are from$ 9.93 $ km to$ 13.32 $ km. The central density of heavier neutron star is smaller. It is$ 0.66 $ fm−3 for NL3 set, while it becomes$ 1.28 $ fm−3 in DDVTD set. The radius at$1.4~M_\odot$ from DDVTD set has the smallest value,$ 11.46 $ km. Therefore, its dimensionless tidal deformability at$1.4~M_\odot$ is just$ 275 $ .Table 6. Neutron star and hyperonic star properties from various RMF models.
Model Neutron star Hyperonic star $1^{\rm{st}}$ threshold/${\rm{fm}}^{-3}$ $M_{\rm{max}}/M_{\odot}$ $R_{\rm{max}}/{\rm{km}}$ $\rho_{c}/{\rm{fm}}^{-3}$ $R_{ 1.4}/{\rm{km}}$ $\rho_{1.4}/{\rm{fm}}^{-3}$ $\varLambda_{ 1.4}$ $M_{\rm{max}}/M_{\odot}$ $R_{\rm{max}}/{\rm{km}}$ $\rho_{c}/{\rm{fm}}^{-3}$ $R_{ 1.4}/{\rm{km}}$ $\rho_{1.4}/{\rm{fm}}^{-3}$ $\varLambda_{ 1.4}$ NL3 2.7746 13.3172 0.6638 14.6433 0.2715 1280 2.3354 12.5105 0.8129 14.6426 0.2715 1280 0.2804 BigApple 2.6005 12.3611 0.7540 12.8745 0.3295 738 2.2186 11.6981 0.8946 12.8750 0.3295 738 0.3310 TM1 2.1797 12.3769 0.8510 14.2775 0.3200 1050 1.8608 11.9255 0.9736 14.2775 0.3218 1050 0.3146 IUFSU 1.9394 11.1682 1.0170 12.3865 0.4331 510 1.6865 10.8653 1.1202 12.3520 0.4705 498 0.3800 DD-LZ1 2.5572 12.2506 0.7789 13.0185 0.3294 729 2.1824 11.6999 0.9113 12.0185 0.3294 729 0.3294 DD-MEX 2.5568 12.3347 0.7706 13.2510 0.3228 785 2.1913 11.8640 0.8890 13.2510 0.3228 785 0.3264 DD-ME2 2.4832 12.0329 0.8177 13.0920 0.3410 716 2.1303 11.6399 0.9296 13.0920 0.3410 716 0.3402 DD-ME1 2.4429 11.9085 0.8358 13.0580 0.3512 682 2.0945 11.5089 0.9560 13.0578 0.3526 681 0.3466 DD2 2.4171 11.8520 0.8481 13.0638 0.3528 686 2.0558 11.3446 0.9922 13.0630 0.3585 685 0.3387 PKDD 2.3268 11.7754 0.8823 13.5493 0.3546 758 1.9983 11.3789 1.0188 13.5400 0.3642 756 0.3264 TW99 2.0760 10.6117 1.0917 12.1805 0.4720 409 1.7135 10.0044 1.3466 11.9880 0.5710 352 0.3696 DDV 1.9319 10.3759 1.1879 12.3060 0.5035 395 1.5387 9.0109 1.7317 10.8990 0.9538 136 0.3547 DDVT 1.9253 10.0846 1.2245 11.6058 0.5458 302 1.5909 9.6244 1.4675 11.4515 0.6660 266 0.4465 DDVTD 1.8507 9.9294 1.2789 11.4615 0.5790 275 1.4956 9.3019 1.6071 10.9880 0.8570 182 0.4465 Now, the maximum masses of hyperonic stars are
$1.50 \sim 2.34~ M_\odot$ , and the corresponding radii are in the range of$9.30 \sim 12.51$ km, which are reduced compared to the cases without considering the strangeness degree of freedom. The central densities become larger compared to those of neutron stars. The smallest radius of the hyperonic star at$ 1.4~M_\odot $ is$ 10.90 $ km from DDV, whose dimensionless tidal deformability is just$ 136 $ . The threshold density of the first onset hyperon is also shown to demonstrate the influences of hyperon on the low mass hyperonic star. In general, the maximum mass of a hyperonic star can exceed$ 2~M_\odot $ if the EoS is a hard type, whose maximum mass approaches$ 2.3~M_\odot $ for a neutron star. Therefore, one solution to the ''hyperon puzzle'' is to adopt the stiff EoS. The softer EoS only can describe the hyperonic star whose mass is around$ 1.5~M_\odot $ . -
In recent work, Rong et al.[146] found that the coupling ratio between the scalar meson and
$ \varLambda $ hyperon,$ R_{\sigma \varLambda} $ , has a strong correlation with that between the vector meson and$ \varLambda $ hyperon,$ R_{\omega \varLambda} $ in the available hypernuclei investigations by reproducing the single-$ \varLambda $ binding energies from relevant experiments. This correlation is easily understood in the RMF framework since the single hyperon-nucleon potential given in Eq. (33), the single hyperon-nucleon potential is dependent on the scalar field and vector one. From the present observables of$ \varLambda $ hypernuclei, we can extract that the$U^N_\varLambda \sim -30$ MeV at nuclear saturation density,$ \rho_0 $ . On the other hand, the$ \sigma_0 $ and$ \omega_0 $ are solved in the symmetry nuclear matter, which are constants. Therefore,$ R_{\sigma \varLambda} $ and$ R_{\omega \varLambda} $ should satisfy the linear relation, when the$ U^N_\varLambda $ is fixed in a RMF parameter set.In this subsection, the TM1 parameter set for NN interaction will be adopted as an example to discuss the impact of the magnitudes of
$ R_{\sigma Y} $ and$ R_{\omega Y} $ on the properties of hyperonic star under the constraints of YN potential at nuclear saturation density,$ U^N_Y(\rho_0) $ . From Eq. (33), we can find a linear relation between the ratios$ R_{\sigma Y} $ and$ R_{\omega Y} $ ($ Y = \varLambda,\; \varSigma,\; \varXi $ ) for different hyperons. In TM1 parameter set, the magnitudes of the scalar potential,$ U_S = g_{\sigma N}\sigma^0 $ and the vector potential,$ U_V = g_{\omega N}\omega^0 $ for nucleons are$ 342.521 $ MeV and$ 274.085 $ MeV at nuclear saturation density, respectively. With the empirical hyperon-nucleon potentials for$ \varLambda,\; \varSigma $ and$ \varXi $ hyperons at nuclear saturation density,$ U_{\varLambda}^N = -30 $ MeV,$ U_{\varSigma}^N = +30 $ MeV and$ U_{\varXi}^N = -14 $ MeV, the following relations are obtained,$$ R_{\omega\varLambda} = 1.249\;69\,R_{\sigma\varLambda}-0.109\;46, $$ (35) $$ R_{\omega\varSigma} = 1.249\;69\,R_{\sigma\varSigma}+0.109\;46, $$ (36) $$ R_{\omega\varXi} = 1.249\;69\,R_{\sigma\varXi}-0.051\;08. $$ (37) Here the strange mesons
$ \sigma^* $ and$ \phi $ are not considered. Therefore, we can adjust the values of$ R_{\omega Y} $ and generate the corresponding$ R_{\sigma Y} $ simultaneously. To study the influences of$ R_{\omega Y} $ on hyperonic star,$ R_{\omega\varLambda},\; R_{\omega\varXi}, \; R_{\omega\varSigma} = 0.6,\; 0.8,\; 1.0 $ are discussed, respectively. Therefore, there are 27 combination cases. The EoSs of hyperonic star matter from TM1 model with different$ R_{\omega\varLambda},\; R_{\omega\varXi},\; R_{\omega\varSigma} $ are plotted in Fig. 7. In general, the EoS becomes stiffer with the$ R_{\omega\varLambda} $ increasing. For the$ \varSigma $ and$ \varXi $ coupling ratios, there are also similar behaviors. It demonstrates that the vector potential increases faster than the scalar one at the high-density region so that the EoS obtains more repulsive contributions from the vector meson.Figure 7. (color online) The EoSs of hyperonic star matter from TM1 models with different
$R_{\omega\varLambda},~R_{\omega\varXi},~R_{\omega\varSigma}$ .In Fig. 8, the pressures and speeds of sound of hyperonic star matter as functions of baryon density with different
$ R_{\omega\varLambda},\; R_{\omega\varXi},\; R_{\omega\varSigma} $ are given. The thresholds of the first hyperon onset are symbolized by the filled diamonds. When the$ R_{\omega\varLambda} $ is larger, the appearances of$ \varLambda $ hyperons are later. Furthermore, the speeds of the sound of hyperonic matter are also strongly dependent on the magnitudes of$ R_{\omega\varLambda},\; R_{\omega\varXi},\; R_{\omega\varSigma} $ . The discontinuous places in these curves about the speeds of sound are generated by the onset of hyperons, which can reduce$ c^2_{\rm s}$ . Therefore, the speed of sound of hyperonic star matter becomes very smaller, once the types of hyperons in hyperonic stars are raised more.Figure 8. (color online) The pressure of hyperonic matter as a function of baryon density with different
$R_{\omega\varLambda},~R_{\omega\varXi},~R_{\omega\varSigma}$ . The corresponding speeds of sound in units of the speed of light shown in sub-figure. The threshold of the first hyperon is indicated by the filled diamonds. The meaning of the curves are same as those in Fig. 7.In Fig. 9, the mass-radius (
$ M-R $ ) and mass-central density ($ M-\rho_{{\rm{B}}} $ ) relations from TM1 model with different$ R_{\omega\varLambda},\; R_{\omega\varXi},\; R_{\omega\varSigma} $ are shown in panel (a) and (b), respectively. The maximum mass of neutron star from the TM1 parameter set is$ 2.18~M_\odot $ . When the hyperons are included, the maximum masses of the hyperonic star are reduced. They are just around$ 1.67~M_\odot $ when$ R_{\omega\varLambda} = 0.6 $ . With the increment of$ R_{\omega\varLambda} $ , the maximum mass of the hyperonic star becomes larger due to the stronger repulsive fields. It is around$ 2.0~M_\odot $ in the case of$ R_{\omega\varLambda} = 1.0 $ , which satisfies the constraints from the recent massive neutron star observables. The corresponding radii turn smaller and the central densities get larger.Figure 9. (color online) The hyperonic star masses as functions of radius and the central baryon density for TM1 models with different
$R_{\omega\varLambda},~R_{\omega\varXi},~R_{\omega\varSigma}$ . The threshold of the first hyperon is indicated by the filled diamonds.Finally, the thresholds of hyperons and properties of hyperonic star with different
$ R_{\omega\varLambda},\; R_{\omega\varXi},\; R_{\omega\varSigma} $ are shown in Table 7. In all of these 27 cases, the$ \varLambda $ hyperon firstly appears in the hyperonic star. Then, if$R_{\omega\varXi} > R_{\omega\varSigma}$ , the$ \varSigma^- $ hyperon will secondly emerge. Otherwise, the$ \varXi^- $ hyperon appears. Furthermore, when$R_{\omega\varXi} < R_{\omega\varSigma}$ , the$ \varXi^0 $ can more easily arises comparing to$ \varSigma^0 $ and$ \varSigma^+ $ hyperons. The maximum masses of hyperonic star and onset density of$ \varLambda $ hyperon are strongly dependent on the$ R_{\omega\varLambda} $ ratio. It can approach$2.04~M_\odot$ when$ R_{\omega\varLambda} = 1.0,\; R_{\omega\varXi} = 1.0,\; R_{\omega\varSigma} = 1.0 $ . The$ \varLambda $ hyperon appears at$ \rho_{{\rm{B}}} = 0.3089 $ fm−3 for$ R_{\omega\varLambda} = 0.6 $ , which is lower than the density of$ 1.4 M_\odot $ neutron star. Therefore, the radii and dimensionless tidal deformability at$1.4~M_\odot$ ,$ R_{1.4} $ and$ \varLambda_{1.4} $ , are slightly changed as 12.277 0 km and 1 055 from the neutron star 12.277 5 km and 1 050. Therefore, the magnitudes of$ R_{\omega\varLambda},\; R_{\omega\varXi},\; R_{\omega\varSigma} $ are significant to determine the maximum mass and corresponding radius of the hyperonic star, while it cannot by fixed very well through present hypernuclei experiments.Table 7. Thresholds and hyperonic star properties from TM1 model with different
$R_{\omega\varLambda}, R_{\omega\varXi}, R_{\omega\varSigma}$ . The hyperons exist in the hyperonic star are given by bold.$R_{\omega\varLambda}$ $R_{\omega\varXi}$ $R_{\omega\varSigma}$ Hyperon thresholds/$/{\rm{fm}}^{-3}$ $M_{\rm{max}}$ $R_{\rm{max}}/{\rm{km}}$ $\rho_{c}/{\rm{fm}}^{-3}$ $R_{1.4}/{\rm{km}}$ $\rho_{1.4}/({\rm{fm} }^{-3})$ $\varLambda_{1.4}$ 0.6 0.6 0.6 ${ {\boldsymbol{\varLambda} } ({\bf{0.3089} }),\;{\boldsymbol{\varXi} }^-({\bf{0.5245} })},\; \varSigma^- (0.9032),\; \varXi^0(1.0710),\; \varSigma^0(1.4447)$ 1.6645 13.2465 0.7251 12.2770 0.3255 1055 0.6 0.6 0.8 ${{\boldsymbol{\varLambda}}({\bf{0.3089}}),\;{\boldsymbol{\varXi}}^-({\bf{0.5245}})},\;\varXi^0 (1.0759) $ 1.6645 13.2465 0.7251 12.2770 0.3255 1055 0.6 0.6 1.0 ${{\boldsymbol{\varLambda}}({\bf{0.3089}}),\;{\boldsymbol{\varXi}}^-({\bf{0.5245}})},\;\varXi^0(1.0759)$ 1.6645 13.2465 0.7251 12.2770 0.3255 1055 0.6 0.8 0.6 ${{\boldsymbol{\varLambda}}({\bf{0.3089}}),\;{\boldsymbol{\varSigma}}^-({\bf{0.6106}}),\;{\boldsymbol{\varXi}}^-({\bf{0.6394}})},\;\varXi^0 (1.3176),\;\varSigma^0 (1.3237)$ 1.6733 13.1347 0.7456 12.2770 0.3255 1055 0.6 0.8 0.8 ${{\boldsymbol{\varLambda}}({\bf{0.3089}}),\;{\boldsymbol{\varXi}}^-({\bf{0.6306}})},\;\varSigma^-(1.2072),\;\varXi^0(1.3924),\;\varSigma^0 (1.8611)$ 1.6742 13.1101 0.7456 12.2770 0.3255 1055 0.6 0.8 1.0 ${{\boldsymbol{\varLambda}}({\bf{0.3089}}),\;{\boldsymbol{\varXi}}^-({\bf{0.6306}})},\;\varXi^0(1.3989)$ 1.6742 13.1101 0.7456 12.2770 0.3255 1055 0.6 1.0 0.6 ${{\boldsymbol{\varLambda}}({\bf{0.3089}}),\;{\boldsymbol{\varSigma}}^-({\bf{0.6106}})},\;\varSigma^0(1.2995),\;\varSigma^+(1.4989) $ 1.6736 13.1111 0.7514 12.2770 0.3255 1055 0.6 1.0 0.8 ${{\boldsymbol{\varLambda}}({\bf{0.3089}})},\;\varSigma^-(0.7830),\;\varXi^-(0.8546),\;\varSigma^0(1.7530),\;\varXi^0(1.8356)$ 1.6757 13.0391 0.7635 12.2770 0.3255 1055 0.6 1.0 1.0 ${{\boldsymbol{\varLambda}}({\bf{0.3089}})},\;\varXi^-(0.8237),\;\varSigma^-(1.7052),\;\varXi^0(1.8870)$ 1.6757 13.0391 0.7635 12.2770 0.3255 1055 0.8 0.6 0.6 ${{\boldsymbol{\varLambda}}({\bf{0.3294}}),\;{\boldsymbol{\varXi}}^-({\bf{0.4485}}),\;{\boldsymbol{\varSigma}}^-({\bf{0.6979}})},\;\varXi^0(0.8050),\;\varSigma^0(1.0959)$ 1.8225 13.0424 0.7615 12.2775 0.3200 1050 0.8 0.6 0.8 ${{\boldsymbol{\varLambda}}({\bf{0.3294}}),\;{\boldsymbol{\varXi}}^- ({\bf{0.4485}})},\;\varXi^0(0.8087)$ 1.8225 13.0423 0.7612 12.2775 0.3200 1050 0.8 0.6 1.0 ${{\boldsymbol{\varLambda}}({\bf{0.3294}}),\;{\boldsymbol{\varXi}}^-({\bf{0.4485}})},\;\varXi^0(0.8087)$ 1.8225 13.0423 0.7612 12.2775 0.3200 1050 0.8 0.8 0.6 ${{\boldsymbol{\varLambda}}({\bf{0.3294}}),\;{\boldsymbol{\varSigma}}^-({\bf{0.5009}}),\;{\boldsymbol{\varXi}}^-({\bf{0.5150}})},\;\varXi^0(0.9242),\;\varSigma^0(0.9501)$ 1.8547 12.8733 0.7972 12.2775 0.3200 1050 0.8 0.8 0.8 ${{\boldsymbol{\varLambda}}({\bf{0.3294}}),\;{\boldsymbol{\varXi}}^-({\bf{0.5103}})},\;\varSigma^-(0.8429),\;\varXi^0(0.9545),\;\varSigma^0(1.3483)$ 1.8619 12.7947 0.8135 12.2775 0.3200 1050 0.8 0.8 1.0 ${{\boldsymbol{\varLambda}}({\bf{0.3294}}),\;{\boldsymbol{\varXi}}^-({\bf{0.5103}})},\;\varXi^0(0.9589)$ 1.8619 12.7947 0.8135 12.2775 0.3200 1050 0.8 1.0 0.6 ${{\boldsymbol{\varLambda}}({\bf{0.3294}}),\;{\boldsymbol{\varSigma}}^-({\bf{0.5009}})},\;\varSigma^0(0.9200),\;\varSigma^+(1.0661),\;\varXi^-(1.1906)$ 1.8603 12.8329 0.8026 12.2775 0.3200 1050 0.8 1.0 0.8 ${{\boldsymbol{\varLambda}}({\bf{0.3294}}),\;{\boldsymbol{\varSigma}}^-({\bf{0.5967}}),\;{\boldsymbol{\varXi}}^-({\bf{0.6220}})},\;\varSigma^0(1.1906),\;\varXi^0(1.2128)$ 1.8799 12.6868 0.8316 12.2775 0.3200 1050 0.8 1.0 1.0 ${{\boldsymbol{\varLambda}}({\bf{0.3294}}),\;{\boldsymbol{\varXi}}^-({\bf{0.6135}})},\;{{\varSigma}}^-({{1.1163}}),\;\varXi^0(1.2699),\;\varSigma^0(1.8870)$ 1.8828 12.6492 0.8371 12.2775 0.3200 1050 1.0 0.6 0.6 ${{\boldsymbol{\varLambda}}({\bf{0.3579}}),\;{\boldsymbol{\varXi}}^-({\bf{0.4186}}),\;{\boldsymbol{\varSigma}}^-({\bf{0.6050}}),\;{\boldsymbol{\varXi}}^{\bf{0}}({\bf{0.6947}})},\;\varSigma^0(0.9589)$ 1.9170 13.0352 0.7661 12.2775 0.3200 1050 1.0 0.6 0.8 ${{\boldsymbol{\varLambda}}({\bf{0.3579}}),\;{\boldsymbol{\varXi}}^-({\bf{0.4128}}),\;{\boldsymbol{\varXi}}^{\bf{0}}({\bf{0.6979}})},\;\varSigma^-(1.4852),\;\varSigma^0(1.5409)$ 1.9174 12.9932 0.7795 12.2775 0.3200 1050 1.0 0.6 1.0 ${{\boldsymbol{\varLambda}}({\bf{0.3579}}),\;{\boldsymbol{\varXi}}^-({\bf{0.4128}}),\;{\boldsymbol{\varXi}}^{\bf{0}} ({\bf{0.6979}})}$ 1.9174 12.9932 0.7795 12.2775 0.3200 1050 1.0 0.8 0.6 ${{\boldsymbol{\varLambda}}({\bf{0.3579}}),\;{\boldsymbol{\varSigma}}^-({\bf{0.4506}}),\;{\boldsymbol{\varXi}}^-({\bf{0.4590}}),\;{\boldsymbol{\varXi}}^{\bf{0}}({\bf{0.7617}}),\;{\boldsymbol{\varSigma}}^{\bf{0}}({\bf{0.8013}})}$ 1.9736 12.8272 0.8047 12.2775 0.3200 1050 1.0 0.8 0.8 ${{\boldsymbol{\varLambda}}({\bf{0.3579}}),\;{\boldsymbol{\varXi}}^-({\bf{0.4548}}),\;{\boldsymbol{\varSigma}}^-({\bf{0.6947}}),\;{\boldsymbol{\varXi}}^{\bf{0}}({\bf{0.7759}})},\;\varSigma^0(1.1061)$ 1.9878 12.7682 0.8093 12.2775 0.3200 1050 1.0 0.8 1.0 ${{\boldsymbol{\varLambda}}({\bf{0.3579}}),\;{\boldsymbol{\varXi}}^-({\bf{0.4548}}),\;{\boldsymbol{\varXi}}^{\bf{0}}({\bf{0.7759}})}$ 1.9879 12.7682 0.8093 12.2775 0.3200 1050 1.0 1.0 0.6 ${{\boldsymbol{\varLambda}}({\bf{0.3579}}),\;{\boldsymbol{\varSigma}}^-({\bf{0.4506}}),\;{\boldsymbol{\varXi}}^-({\bf{0.6726}}),\;{\boldsymbol{\varSigma}}^{\bf{0}}({\bf{0.7617}})},\;\varSigma^+(0.8826)$ 1.9898 12.7706 0.8146 12.2775 0.3200 1050 1.0 1.0 0.8 ${{\boldsymbol{\varLambda}}({\bf{0.3579}}),\;{\boldsymbol{\varSigma}}^-({\bf{0.5126}}),\;{\boldsymbol{\varXi}}^-({\bf{0.5221}})},\;\varXi^0(0.9074),\;\varSigma^0(0.9328)$ 2.0275 12.6470 0.8254 12.2775 0.3200 1050 1.0 1.0 1.0 ${{\boldsymbol{\varLambda}}({\bf{0.3579}}),\;{\boldsymbol{\varXi}}^-({\bf{0.5197}})},\;\varSigma^-(0.8546),\;\varXi^0(0.9328),\;\varSigma^0(1.4447)$ 2.0363 12.5920 0.8327 12.2775 0.3200 1050
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摘要: 随着引力波探测以及对中子星质量与半径的高精度测量,中子星作为超新星爆发的剩余产物正吸引着相关领域的高度关注。在中子星的内核部分,诸如超子之类的奇异自由度有可能会出现从而形成超子星。本工作在相对论平均场模型框架下研究由核子与轻子构成的中子星以及包含超子的超子星。采用目前常用的非线性相对论平均场以及密度依赖的相对论平均场参数研究了超子对超子星质量、半径、潮汐形变等性质的影响。最后讨论了介子与超子的耦合常数对超子星性质的影响,发现当矢量介子与超子耦合系数较强时,利用现有的相对论平均场模型参数可以获得大质量的超子星。Abstract: The neutron star as a supernova remnant is attracting high attention recently due to the gravitation wave detection and precise measurements about its mass and radius. In the inner core region of the neutron star, the strangeness degrees of freedom, such as the hyperons, can be present, which is also named as a hyperonic star. In this work, the neutron star consisting of nucleons and leptons, and the hyperonic star including the hyperons will be studied in the framework of the relativistic mean-field(RMF) model. Some popular non-linear and density-dependent RMF parametrizations will be adopted to investigate the role of hyperons in a hyperonic star on its mass, radius, tidal deformability, and other properties. Finally, the coupling strengths between mesons and hyperons are also discussed, which can generate the massive hyperonic star with present RMF parameter sets, when the vector coupling constants are strong.
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Key words:
- neutron star /
- relativistic mean-field model /
- hyperonic star
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Figure 1. (color online) The pressure
$P$ versus energy density$\varepsilon$ of neutron star matter and hyperonic star matter from NLRMF and DDRMF models. The joint constraints on EoS extracted from the GW170817 and GW190814 are shown as a shaded green band. Panels (a) and panel (b) for the neutrons star matter from the NLRMF and DDRMF models, respectively. Panels (c) and panel (d) for the hyperonic star matter from the NLRMF and DDRMF models, respectively.Figure 2. (color online) EoSs of neutron star and hyperonic star matter with different NLRMF and DDRMF models. The corresponding speeds of sound in units of the speed of light shown in the insert. Panels (a) and panel (b) for the neutrons star matter from the NLRMF and DDRMF models, respectively. Panels (c) and panel (d) for the hyperonic star matter from the NLRMF and DDRMF models, respectively.
Figure 5. (color online) The neutron and hyperonic star masses as functions of radius for NLRMF and DDRMF sets. Constraints from astronomical observables for the massive neutron star, NICER, and GW170817 are also shown. Panels (a) and panel (b) for the neutrons star matter from the NLRMF and DDRMF models, respectively. Panels (c) and panel (d) for the hyperonic star matter from the NLRMF and DDRMF models, respectively.
Figure 6. (color online) The dimensionless tidal deformability as a function of star mass for NLRMF and DDRMF sets. The constraints from GW170817 event for tidal deformability is shown. Panels (a) and panel (b) for the neutrons star matter from the NLRMF and DDRMF models, respectively. Panels (c) and panel (d) for the hyperonic star matter from the NLRMF and DDRMF models, respectively.
Figure 8. (color online) The pressure of hyperonic matter as a function of baryon density with different
$R_{\omega\varLambda},~R_{\omega\varXi},~R_{\omega\varSigma}$ . The corresponding speeds of sound in units of the speed of light shown in sub-figure. The threshold of the first hyperon is indicated by the filled diamonds. The meaning of the curves are same as those in Fig. 7.Table 1. Masses of nucleons and mesons, meson coupling constants in various NLRMF models.
Parameter NL3[126] BigApple[127] TM1[103] IUFSU[113] $m_n$/MeV 939.000 0 939.000 0 938.000 0 939.000 0 $m_p$/MeV 939.000 0 939.000 0 938.000 0 939.000 0 $m_{\sigma}$/MeV 508.194 0 492.730 0 511.198 0 491.500 0 $m_{\omega}$/MeV 782.501 0 782.500 0 783.000 0 782.500 0 $m_{\rho}$/MeV 763.000 0 763.000 0 770.000 0 763.000 0 $g_{\sigma}$ 10.217 0 9.669 9 10.028 9 9.971 3 $g_{\omega}$ 12.868 0 12.316 0 12.613 9 13.032 1 $g_{\rho}$ 8.948 0 14.161 8 9.264 4 13.589 9 $g_2/\rm fm^{-1}$ 10.431 0 11.921 4 7.232 5 8.492 9 $g_3$ −28.885 0 −31.679 6 0.618 3 0.487 7 $c_3$ 0.000 0 2.684 3 71.307 5 144.219 5 $\varLambda_V$ 0.000 0 0.047 5 0.000 0 0.046 0 Table 2. Masses of nucleons and mesons, meson coupling constants, and the nuclear saturation densities in various DDRMF models.
Parameter DD-LZ1[121] DD-MEX[117] DD-ME2[116] DD-ME1[115] DD2[114] PKDD[118] TW99[119] DDV[120] DDVT[120] DDVTD[120] $m_n$/MeV 938.9000 939.0000 939.0000 939.0000 939.5654 939.5731 939.0000 939.5654 939.5654 939.5654 $m_p$/MeV 938.9000 939.0000 939.0000 939.0000 938.2720 938.2796 939.0000 938.2721 938.2721 938.2721 $m_{\sigma}$/MeV 538.6192 547.3327 550.1238 549.5255 546.2125 555.5112 550.0000 537.6001 502.5986 502.6198 $m_{\omega}$/MeV 783.0000 783.0000 783.0000 783.0000 783.0000 783.0000 783.0000 783.0000 783.0000 783.0000 $m_{\rho}$/MeV 769.0000 763.0000 763.0000 763.0000 763.0000 763.0000 763.0000 763.0000 763.0000 763.0000 $m_{\delta}$/MeV — — — — — — — — — 980.0000 $\varGamma_{\sigma}(0)$ 12.0014 — — — — — — — — — $\varGamma_{\omega}(0)$ 14.2925 — — — — — — — — — $\varGamma_{\rho}(0)$ 15.1509 — — — — — — — — — $\varGamma_{\delta}(0)$ — — — — — — — — — — $\varGamma_{\sigma}(\rho_{{\rm{B}}0})$ — 10.7067 10.5396 10.4434 10.6867 10.7385 10.7285 10.1370 8.3829 8.3793 $\varGamma_{\omega}(\rho_{{\rm{B}}0})$ — 13.3388 13.0189 12.8939 13.3424 13.1476 13.2902 12.7705 10.9871 10.9804 $\varGamma_{\rho}(\rho_{{\rm{B}}0})$ — 7.2380 7.3672 7.6106 7.2539 8.5996 7.3220 7.8483 7.6971 8.0604 $\varGamma_{\delta}(\rho_{{\rm{B}}0})$ — — — — — — — — — 0.8487 $\rho_{{\rm{B}}0}/{\rm{fm}}^{-3}$ 0.1581 0.1520 0.1520 0.1520 0.1490 0.1496 0.1530 0.1511 0.1536 0.1536 $a_{\sigma}$ 1.0627 1.3970 1.3881 1.3854 1.3576 1.3274 1.3655 1.2100 1.2040 1.1964 $b_{\sigma}$ 1.7636 1.3350 1.0943 0.9781 0.6344 0.4351 0.2261 0.2129 0.1921 0.1917 $c_{\sigma}$ 2.3089 2.0671 1.7057 1.5342 1.0054 0.6917 0.4097 0.3080 0.2777 0.2738 $d_{\sigma}$ 0.3800 0.4016 0.4421 0.4661 0.5758 0.6942 0.9020 1.0403 1.0955 1.1034 $a_{\omega}$ 1.0592 1.3936 1.3892 1.3879 1.3697 1.3422 1.4025 1.2375 1.1608 1.1669 $b_{\omega}$ 0.4183 1.0191 0.9240 0.8525 0.4965 0.3712 0.1726 0.0391 0.0446 0.0264 $c_{\omega}$ 0.5387 1.6060 1.4620 1.3566 0.8178 0.6114 0.3443 0.0724 0.0672 0.0423 $d_{\omega}$ 0.7866 0.4556 0.4775 0.4957 0.6385 0.7384 0.9840 2.1457 2.2269 2.8062 $a_{\rho}$ 0.7761 0.6202 0.5647 0.5008 0.5189 0.1833 0.5150 0.3527 0.5487 0.5580 $a_{\delta}$ — — — — — — — — — 0.5580 Table 3. Nuclear matter properties at saturation density generated by NLRMF and DDRMF parameterizations.
Model $\rho_{{\rm{B}}0}/{\rm{fm}}^{-3}$ $E/A$/MeV $K_0$/MeV $E_{{\rm{sym}}}$/MeV $L_0$/MeV $M_{\rm n}^{*}/M$ $M_{\rm p}^{*}/M$ NL3 0.1480 −16.2403 269.9605 37.3449 118.3225 0.5956 0.5956 BigApple 0.1545 −16.3436 226.2862 31.3039 39.7407 0.6103 0.6103 TM1 0.1450 −16.2631 279.5858 36.8357 110.6082 0.6348 0.6348 IUFSU 0.1545 −16.3973 230.7491 31.2851 47.1651 0.6095 0.6095 DD-LZ1 0.1581 −16.0598 231.1030 31.3806 42.4660 0.5581 0.5581 DD-MEX 0.1519 −16.0973 267.3819 32.2238 46.6998 0.5554 0.5554 DD-ME2 0.1520 −16.1418 251.3062 32.3094 51.2653 0.5718 0.5718 DD-ME1 0.1522 −16.2328 245.6657 33.0899 55.4634 0.5776 0.5776 DD2 0.1491 −16.6679 242.8509 31.6504 54.9529 0.5627 0.5614 DD2 0.1495 −16.9145 261.7912 36.7605 90.1204 0.5713 0.5699 TW99 0.1530 −16.2472 240.2022 32.7651 55.3095 0.5549 0.5549 DDV 0.1511 −16.9279 239.9522 33.5969 69.6813 0.5869 0.5852 DDVT 0.1536 −16.9155 239.9989 31.5585 42.3414 0.6670 0.6657 DDVTD 0.1536 −16.9165 239.9137 31.8168 42.5829 0.6673 0.6660 Table 4. The Coupling constants between hyperons and
$\sigma$ meson,$g_{\sigma Y}$ and$\varLambda$ -$\sigma^*$ ,$g_{\sigma^*\varLambda}$ in different RMF effective interactions.Model $R_{\sigma\varLambda}$ $R_{\sigma\varSigma}$ $R_{\sigma\varXi}$ $R_{\sigma^*\varLambda}$ NL3 0.6189 0.4609 0.3068 0.8470 BigApple 0.6163 0.4528 0.3054 0.8631 TM1 0.6211 0.4459 0.3076 0.8371 IUFSU 0.6162 0.4530 0.3054 0.8880 DD-LZ1 0.6104 0.4657 0.3028 0.8760 DD-MEX 0.6128 0.4692 0.3040 0.8623 DD-ME2 0.6099 0.4607 0.3025 0.8576 DD-ME1 0.6086 0.4572 0.3018 0.8583 DD2 0.6127 0.4666 0.3039 0.8642 PKDD 0.6104 0.4618 0.3027 0.8497 TW99 0.6120 0.4688 0.3036 0.8582 DDV 0.6074 0.4528 0.3011 0.8798 DDVT 0.5912 0.3993 0.2924 0.9226 DDVTD 0.5911 0.3990 0.2924 0.9225 Table 5. Hyperon thresholds calculated with different RMF effective interactions for hyperonic matter. The unit of the density is fm−3.
Model $ 1^{{\rm{st}}}$ ($\rho_{\rm{th}}$) $ 2^{{\rm{nd}}}$ ($\rho_{\rm{th}}$) $ 3^{{\rm{rd}}}$ ($\rho_{\rm{th}}$) $ 4^{{\rm{th}}}$ ($\rho_{\rm{th}}$) NL3 $\varLambda$ (0.2804) $\varXi^-$ (0.6078) $\varXi^0$ (0.9723) $\varSigma^-$(1.3545) BigApple $\varLambda$ (0.3310) $\varSigma^-$ (0.4895) $\varXi^-$ (0.6191) $\varXi^0$ (1.2758) TM1 $\varLambda$ (0.3146) $\varSigma^-$ (0.9995) $\varXi^-$ (1.0228) IUFSU $\varLambda$ (0.3800) $\varSigma^-$ (0.5645) DD-LZ1 $\varLambda$ (0.3294) $\varSigma^-$ (0.4034) $\varXi^-$ (0.6106) $\varXi^0$ (1.2935) DD-MEX $\varLambda$ (0.3264) $\varSigma^-$ (0.3871) $\varXi^-$ (0.5967) $\varXi^0$ (1.2699) DD-ME2 $\varLambda$ (0.3402) $\varSigma^-$ (0.4244) $\varXi^-$ (0.4895) $\varXi^0$ (1.3237) DD-ME1 $\varLambda$ (0.3466) $\varSigma^-$ (0.4424) $\varXi^-$ (0.4740) $\varXi^0$ (1.3545) DD2 $\varLambda$ (0.3387) $\varSigma^-$ (0.4147) $\varXi^-$ (0.5699) $\varXi^0$ (1.3733) PKDD $\varLambda$ (0.3264) $\varXi^-$ (0.4016) $\varSigma^-$ (0.5126) $\varXi^0$ (1.0759) TW99 $\varLambda$ (0.3696) $\varSigma^-$ (0.4167) $\varXi^-$ (0.7109) $\varXi^0$ (1.7052) DDV $\varLambda$ (0.3547) $\varSigma^-$ (0.4850) $\varXi^-$ (0.7723) DDVT $\varLambda$ (0.4465) $\varXi^-$ (0.4941) $\varSigma^-$ (0.6220) DDVTD $\varLambda$ (0.4465) $\varXi^-$ (0.4963) $\varSigma^-$ (0.6163) Table 6. Neutron star and hyperonic star properties from various RMF models.
Model Neutron star Hyperonic star $1^{\rm{st}}$ threshold/${\rm{fm}}^{-3}$ $M_{\rm{max}}/M_{\odot}$ $R_{\rm{max}}/{\rm{km}}$ $\rho_{c}/{\rm{fm}}^{-3}$ $R_{ 1.4}/{\rm{km}}$ $\rho_{1.4}/{\rm{fm}}^{-3}$ $\varLambda_{ 1.4}$ $M_{\rm{max}}/M_{\odot}$ $R_{\rm{max}}/{\rm{km}}$ $\rho_{c}/{\rm{fm}}^{-3}$ $R_{ 1.4}/{\rm{km}}$ $\rho_{1.4}/{\rm{fm}}^{-3}$ $\varLambda_{ 1.4}$ NL3 2.7746 13.3172 0.6638 14.6433 0.2715 1280 2.3354 12.5105 0.8129 14.6426 0.2715 1280 0.2804 BigApple 2.6005 12.3611 0.7540 12.8745 0.3295 738 2.2186 11.6981 0.8946 12.8750 0.3295 738 0.3310 TM1 2.1797 12.3769 0.8510 14.2775 0.3200 1050 1.8608 11.9255 0.9736 14.2775 0.3218 1050 0.3146 IUFSU 1.9394 11.1682 1.0170 12.3865 0.4331 510 1.6865 10.8653 1.1202 12.3520 0.4705 498 0.3800 DD-LZ1 2.5572 12.2506 0.7789 13.0185 0.3294 729 2.1824 11.6999 0.9113 12.0185 0.3294 729 0.3294 DD-MEX 2.5568 12.3347 0.7706 13.2510 0.3228 785 2.1913 11.8640 0.8890 13.2510 0.3228 785 0.3264 DD-ME2 2.4832 12.0329 0.8177 13.0920 0.3410 716 2.1303 11.6399 0.9296 13.0920 0.3410 716 0.3402 DD-ME1 2.4429 11.9085 0.8358 13.0580 0.3512 682 2.0945 11.5089 0.9560 13.0578 0.3526 681 0.3466 DD2 2.4171 11.8520 0.8481 13.0638 0.3528 686 2.0558 11.3446 0.9922 13.0630 0.3585 685 0.3387 PKDD 2.3268 11.7754 0.8823 13.5493 0.3546 758 1.9983 11.3789 1.0188 13.5400 0.3642 756 0.3264 TW99 2.0760 10.6117 1.0917 12.1805 0.4720 409 1.7135 10.0044 1.3466 11.9880 0.5710 352 0.3696 DDV 1.9319 10.3759 1.1879 12.3060 0.5035 395 1.5387 9.0109 1.7317 10.8990 0.9538 136 0.3547 DDVT 1.9253 10.0846 1.2245 11.6058 0.5458 302 1.5909 9.6244 1.4675 11.4515 0.6660 266 0.4465 DDVTD 1.8507 9.9294 1.2789 11.4615 0.5790 275 1.4956 9.3019 1.6071 10.9880 0.8570 182 0.4465 Table 7. Thresholds and hyperonic star properties from TM1 model with different
$R_{\omega\varLambda}, R_{\omega\varXi}, R_{\omega\varSigma}$ . The hyperons exist in the hyperonic star are given by bold.$R_{\omega\varLambda}$ $R_{\omega\varXi}$ $R_{\omega\varSigma}$ Hyperon thresholds/$/{\rm{fm}}^{-3}$ $M_{\rm{max}}$ $R_{\rm{max}}/{\rm{km}}$ $\rho_{c}/{\rm{fm}}^{-3}$ $R_{1.4}/{\rm{km}}$ $\rho_{1.4}/({\rm{fm} }^{-3})$ $\varLambda_{1.4}$ 0.6 0.6 0.6 ${ {\boldsymbol{\varLambda} } ({\bf{0.3089} }),\;{\boldsymbol{\varXi} }^-({\bf{0.5245} })},\; \varSigma^- (0.9032),\; \varXi^0(1.0710),\; \varSigma^0(1.4447)$ 1.6645 13.2465 0.7251 12.2770 0.3255 1055 0.6 0.6 0.8 ${{\boldsymbol{\varLambda}}({\bf{0.3089}}),\;{\boldsymbol{\varXi}}^-({\bf{0.5245}})},\;\varXi^0 (1.0759) $ 1.6645 13.2465 0.7251 12.2770 0.3255 1055 0.6 0.6 1.0 ${{\boldsymbol{\varLambda}}({\bf{0.3089}}),\;{\boldsymbol{\varXi}}^-({\bf{0.5245}})},\;\varXi^0(1.0759)$ 1.6645 13.2465 0.7251 12.2770 0.3255 1055 0.6 0.8 0.6 ${{\boldsymbol{\varLambda}}({\bf{0.3089}}),\;{\boldsymbol{\varSigma}}^-({\bf{0.6106}}),\;{\boldsymbol{\varXi}}^-({\bf{0.6394}})},\;\varXi^0 (1.3176),\;\varSigma^0 (1.3237)$ 1.6733 13.1347 0.7456 12.2770 0.3255 1055 0.6 0.8 0.8 ${{\boldsymbol{\varLambda}}({\bf{0.3089}}),\;{\boldsymbol{\varXi}}^-({\bf{0.6306}})},\;\varSigma^-(1.2072),\;\varXi^0(1.3924),\;\varSigma^0 (1.8611)$ 1.6742 13.1101 0.7456 12.2770 0.3255 1055 0.6 0.8 1.0 ${{\boldsymbol{\varLambda}}({\bf{0.3089}}),\;{\boldsymbol{\varXi}}^-({\bf{0.6306}})},\;\varXi^0(1.3989)$ 1.6742 13.1101 0.7456 12.2770 0.3255 1055 0.6 1.0 0.6 ${{\boldsymbol{\varLambda}}({\bf{0.3089}}),\;{\boldsymbol{\varSigma}}^-({\bf{0.6106}})},\;\varSigma^0(1.2995),\;\varSigma^+(1.4989) $ 1.6736 13.1111 0.7514 12.2770 0.3255 1055 0.6 1.0 0.8 ${{\boldsymbol{\varLambda}}({\bf{0.3089}})},\;\varSigma^-(0.7830),\;\varXi^-(0.8546),\;\varSigma^0(1.7530),\;\varXi^0(1.8356)$ 1.6757 13.0391 0.7635 12.2770 0.3255 1055 0.6 1.0 1.0 ${{\boldsymbol{\varLambda}}({\bf{0.3089}})},\;\varXi^-(0.8237),\;\varSigma^-(1.7052),\;\varXi^0(1.8870)$ 1.6757 13.0391 0.7635 12.2770 0.3255 1055 0.8 0.6 0.6 ${{\boldsymbol{\varLambda}}({\bf{0.3294}}),\;{\boldsymbol{\varXi}}^-({\bf{0.4485}}),\;{\boldsymbol{\varSigma}}^-({\bf{0.6979}})},\;\varXi^0(0.8050),\;\varSigma^0(1.0959)$ 1.8225 13.0424 0.7615 12.2775 0.3200 1050 0.8 0.6 0.8 ${{\boldsymbol{\varLambda}}({\bf{0.3294}}),\;{\boldsymbol{\varXi}}^- ({\bf{0.4485}})},\;\varXi^0(0.8087)$ 1.8225 13.0423 0.7612 12.2775 0.3200 1050 0.8 0.6 1.0 ${{\boldsymbol{\varLambda}}({\bf{0.3294}}),\;{\boldsymbol{\varXi}}^-({\bf{0.4485}})},\;\varXi^0(0.8087)$ 1.8225 13.0423 0.7612 12.2775 0.3200 1050 0.8 0.8 0.6 ${{\boldsymbol{\varLambda}}({\bf{0.3294}}),\;{\boldsymbol{\varSigma}}^-({\bf{0.5009}}),\;{\boldsymbol{\varXi}}^-({\bf{0.5150}})},\;\varXi^0(0.9242),\;\varSigma^0(0.9501)$ 1.8547 12.8733 0.7972 12.2775 0.3200 1050 0.8 0.8 0.8 ${{\boldsymbol{\varLambda}}({\bf{0.3294}}),\;{\boldsymbol{\varXi}}^-({\bf{0.5103}})},\;\varSigma^-(0.8429),\;\varXi^0(0.9545),\;\varSigma^0(1.3483)$ 1.8619 12.7947 0.8135 12.2775 0.3200 1050 0.8 0.8 1.0 ${{\boldsymbol{\varLambda}}({\bf{0.3294}}),\;{\boldsymbol{\varXi}}^-({\bf{0.5103}})},\;\varXi^0(0.9589)$ 1.8619 12.7947 0.8135 12.2775 0.3200 1050 0.8 1.0 0.6 ${{\boldsymbol{\varLambda}}({\bf{0.3294}}),\;{\boldsymbol{\varSigma}}^-({\bf{0.5009}})},\;\varSigma^0(0.9200),\;\varSigma^+(1.0661),\;\varXi^-(1.1906)$ 1.8603 12.8329 0.8026 12.2775 0.3200 1050 0.8 1.0 0.8 ${{\boldsymbol{\varLambda}}({\bf{0.3294}}),\;{\boldsymbol{\varSigma}}^-({\bf{0.5967}}),\;{\boldsymbol{\varXi}}^-({\bf{0.6220}})},\;\varSigma^0(1.1906),\;\varXi^0(1.2128)$ 1.8799 12.6868 0.8316 12.2775 0.3200 1050 0.8 1.0 1.0 ${{\boldsymbol{\varLambda}}({\bf{0.3294}}),\;{\boldsymbol{\varXi}}^-({\bf{0.6135}})},\;{{\varSigma}}^-({{1.1163}}),\;\varXi^0(1.2699),\;\varSigma^0(1.8870)$ 1.8828 12.6492 0.8371 12.2775 0.3200 1050 1.0 0.6 0.6 ${{\boldsymbol{\varLambda}}({\bf{0.3579}}),\;{\boldsymbol{\varXi}}^-({\bf{0.4186}}),\;{\boldsymbol{\varSigma}}^-({\bf{0.6050}}),\;{\boldsymbol{\varXi}}^{\bf{0}}({\bf{0.6947}})},\;\varSigma^0(0.9589)$ 1.9170 13.0352 0.7661 12.2775 0.3200 1050 1.0 0.6 0.8 ${{\boldsymbol{\varLambda}}({\bf{0.3579}}),\;{\boldsymbol{\varXi}}^-({\bf{0.4128}}),\;{\boldsymbol{\varXi}}^{\bf{0}}({\bf{0.6979}})},\;\varSigma^-(1.4852),\;\varSigma^0(1.5409)$ 1.9174 12.9932 0.7795 12.2775 0.3200 1050 1.0 0.6 1.0 ${{\boldsymbol{\varLambda}}({\bf{0.3579}}),\;{\boldsymbol{\varXi}}^-({\bf{0.4128}}),\;{\boldsymbol{\varXi}}^{\bf{0}} ({\bf{0.6979}})}$ 1.9174 12.9932 0.7795 12.2775 0.3200 1050 1.0 0.8 0.6 ${{\boldsymbol{\varLambda}}({\bf{0.3579}}),\;{\boldsymbol{\varSigma}}^-({\bf{0.4506}}),\;{\boldsymbol{\varXi}}^-({\bf{0.4590}}),\;{\boldsymbol{\varXi}}^{\bf{0}}({\bf{0.7617}}),\;{\boldsymbol{\varSigma}}^{\bf{0}}({\bf{0.8013}})}$ 1.9736 12.8272 0.8047 12.2775 0.3200 1050 1.0 0.8 0.8 ${{\boldsymbol{\varLambda}}({\bf{0.3579}}),\;{\boldsymbol{\varXi}}^-({\bf{0.4548}}),\;{\boldsymbol{\varSigma}}^-({\bf{0.6947}}),\;{\boldsymbol{\varXi}}^{\bf{0}}({\bf{0.7759}})},\;\varSigma^0(1.1061)$ 1.9878 12.7682 0.8093 12.2775 0.3200 1050 1.0 0.8 1.0 ${{\boldsymbol{\varLambda}}({\bf{0.3579}}),\;{\boldsymbol{\varXi}}^-({\bf{0.4548}}),\;{\boldsymbol{\varXi}}^{\bf{0}}({\bf{0.7759}})}$ 1.9879 12.7682 0.8093 12.2775 0.3200 1050 1.0 1.0 0.6 ${{\boldsymbol{\varLambda}}({\bf{0.3579}}),\;{\boldsymbol{\varSigma}}^-({\bf{0.4506}}),\;{\boldsymbol{\varXi}}^-({\bf{0.6726}}),\;{\boldsymbol{\varSigma}}^{\bf{0}}({\bf{0.7617}})},\;\varSigma^+(0.8826)$ 1.9898 12.7706 0.8146 12.2775 0.3200 1050 1.0 1.0 0.8 ${{\boldsymbol{\varLambda}}({\bf{0.3579}}),\;{\boldsymbol{\varSigma}}^-({\bf{0.5126}}),\;{\boldsymbol{\varXi}}^-({\bf{0.5221}})},\;\varXi^0(0.9074),\;\varSigma^0(0.9328)$ 2.0275 12.6470 0.8254 12.2775 0.3200 1050 1.0 1.0 1.0 ${{\boldsymbol{\varLambda}}({\bf{0.3579}}),\;{\boldsymbol{\varXi}}^-({\bf{0.5197}})},\;\varSigma^-(0.8546),\;\varXi^0(0.9328),\;\varSigma^0(1.4447)$ 2.0363 12.5920 0.8327 12.2775 0.3200 1050 -
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