Extended quark mean-field model for neutron stars

Abstract

We extend the quark mean-field (QMF) model to strangeness freedom to study the properties of hyperons ($\Lambda,\Sigma,\Xi$) in infinite baryon matter and neutron star properties. The baryon-scalar meson couplings in the QMF model are determined self-consistently from the quark level, where the quark confinement is taken into account in terms of a scalar-vector harmonic oscillator potential. The strength of such confinement potential for $u,d$ quarks is constrained by the properties of finite nuclei, while the one for $s$ quark is limited by the properties of nuclei with a $\Lambda$ hyperon. These two strengths are not same, which represents the SU(3) symmetry breaking effectively in the QMF model. Also, we use an enhanced $\Sigma$ coupling with the vector meson, and both $\Sigma$ and $\Xi$ hyperon potentials can be properly described in the model. The effects of the SU(3) symmetry breaking on the neutron star structures are then studied. We find that the SU(3) breaking shifts earlier the hyperon onset density and makes hyperons more abundant in the star, in comparisons with the results of the SU(3) symmetry case. However, it does not affect much the star's maximum mass. The maximum masses are found to be $1.62 M_{\odot}$ with hyperons and $1.88 M_{\odot}$ without hyperons. The present neutron star model is shown to have limitations on explaining the recently measured heavy pulsar.Comment: 7 pages, 7 figures, Phys. Rev. C (2014) accepte

Quark mean field model with pion and gluon corrections

“…The maximum masses of neutron star in this work are between 2.25M ⊙ and 2.38M ⊙ , which satisfy the constraint of present astronomical observation data about 2M ⊙ [37]. However, the previous QMF model without pion and gluon corrections, could not provide the large neutron star mass [21]. …”

“…The quarks are confined through some confinement potentials in the QMF model, whose constituent quark mass is around 300 MeV. Shen et al promoted such picture with more precise parameters by fitting the properties of stable finite nuclei [18] and applied it on the study of hypernuclei and neutron stars [19][20][21]. To include the baryon octets, Wang et al introduced a chiral Lagrangian at hadron level in QMF model and studied the properties of strangeness nuclear matter [22][23][24][25][26][27].…”

The $ΞN$ interaction constrained by recent $Ξ^-$ hypernuclei experiments

“…The baryons interact with each other through exchanging mesons and photons in quark mean-field (QMF) model [29][30][31][32]. The Lagrangian can be evaluated as,…”

Hyperon Puzzle: Hints from Quantum Monte Carlo Calculations

“…This leads to a reduction of the Fermi pressure exerted by the baryons and, as a consequence, to a softening of the equation of state (EOS) and to a reduction of the predicted maximum mass.Currently there is no general agreement (even qualitative) among the predicted results for the EOS and the maximum mass of a NS including hyperons. Some of the standard nuclear physics many-body approaches, such as Hartree-Fock [2, 3], Brueckner-Hartree-Fock [4,5] or the extended Quark Mean Field model [6], predict the appearance of hyperons at around (2−3)ρ 0 , ρ 0 = 0.16 fm −3 , and a strong softening of EOS, implying a sizable reduction of the maximum mass. On the other hand, other approaches like relativistic Hartree-Fock [7,8], relativistic mean field models [9][10][11][12][13][14] or quantum hadrodynamics [15] indicate much weaker effects as a consequence of the presence of strange baryons in the core of a NS.…”