Equation of State for Massive Neutron Stars

Abstract

Using relativistic Hartree-Fock approximation, we investigate the properties of the neutron-star matter in detail. In the present calculation, we consider not only the tensor coupling of vector mesons to octet baryons and the form factors at interaction vertexes but also the internal (quark) structure change of baryons in dense matter. The relativistic Hartree-Fock calculations are performed in two ways: one is the calculation with the coupling constants determined by SU(6) (quark model) symmetry, the other is with the coupling constants based on SU(3) (flavor) symmetry. For the latter case, we use the latest Nijmegen (ESC08) model. Then, it is very remarkable that the particle composition of the core matter in SU(3) symmetry is completely different from that in SU(6) symmetry. In SU(6) symmetry, all octet baryons appear in the density region below ∼ 1.2 fm −3 , while, in the ESC08 model, only the Ξ − hyperon is produced. Furthermore, the medium modification of the internal baryon structure hardens the equation of state for the core matter. Taking all these effects into account, we can obtain the maximum neutron-star mass which is consistent with the recently observed mass, 1.97 ± 0.04M ⊙ (PSR J1614-2230). We therefore conclude that the extension from SU(6) symmetry to SU(3) symmetry in the meson-baryon couplings and the internal baryon-structure variation in matter certainly enhance the mass of neutron star. Furthermore, the effects of the form factor at vertex and the Fock contribution including the tensor coupling due to the vector mesons are indispensable to describe the core matter. In particular, the Fock term is very vital in reproducing the preferable value of symmetry energy, a 4 (≃ 30−40 MeV), in nuclear matter.

Constraining the Symmetry Parameters of the Nuclear Interaction

“…The strangeness content would be smaller for less stiff hadronic EOSs and smaller maximum masses. This restriction in the strangeness content of neutron stars is consistent with studies using the chiral quark-meson coupling (Katayama et al 2012) and relativistic mean-field (Bednarek et al 2012) models.…”

Hypernuclear matter in a complete SU(3) symmetry group

“…Another possibility is to use relativistic quantum hadrodynamic (QHD) models [9], where the strong interaction is simulated by the exchange of massive mesons through Yukawa potentials. Whilst most hypernuclear EoS predict neutron star masses below 2 M ⊙ even in QHD [3,[10][11][12][13], a few parametrizations succeed in describing very massive hyperonic neutron stars [14][15][16]. A clever mechanism to increase the maximum mass of neutron stars with hyperons in their core (hyperonic stars) is to include an additional vector meson that mediates the hyperon-hyperon interaction [17,18].…”

Properties of Neutron Stars with Hyperons and Quarks Using Relativistic Hartree–Fock Approximation and MIT Bag Model

“…Using the chiral quark-meson coupling (CQMC) models within relativistic Hatree-Fock approximation, we present the stiff equation of state (EoS) with hyperons, which can support the massive neutron stars [9,10]. We also discuss quark matte contribution by using the MIT bag model [11].…”