EoS for massive neutron stars. (arXiv:1207.1554v1 [astro-ph.SR])

EoS for massive neutron stars. (arXiv:1207.1554v1 [astro-ph.SR]):
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 $\sim 1.2$ fm$^{-3}$, while, in the ESC08 model, only the
\Xi^- 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 \pm 0.04 M_\sun (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 (\simeq 30 - 40 MeV), in nuclear
matter.