arXiv subjects

Tsuyoshi Miyatsu

Publications and source records attributed to Tsuyoshi Miyatsu.

22 records · Page 2Linked to original sources

arXiv2013

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. 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 ($σ^{\ast}$ and $ϕ$) 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. In addition, the strange vector ($ϕ$) meson and the variation of baryon structure in matter also play important roles in supporting a massive neutron star.

nucl-th↗

arXiv2012

Neutron Star Properties in the Chiral Quark-Meson Coupling Model

We study the properties of neutron star using the chiral quark-meson coupling model, in which the quark-quark hyperfine interaction due to the exchanges of gluon and pion based on chiral symmetry is considered. We also examine the effects of hyperons and $Δ$-isobars in a neutron star. Extending the SU(6) spin-flavor symmetry to more general SU(3) flavor symmetry in the vector-meson couplings to baryons, the maximum mass of neutron star can reach the recently observed, massive pulsar mass, $1.97 \pm 0.04 M_{\odot}$. In this calculation, $Λ$ and $Ξ$ are generated in a neutron star, while $Σ$ and $Δ$-isobars do not appear.

nucl-th↗

arXiv2012

EoS for massive neutron stars

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 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 \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.

astro-ph.SR↗

arXiv2011

Effects of Fock term, tensor coupling and baryon structure variation on a neutron star

The equation of state for neutron matter is calculated within relativistic Hartree-Fock approximation. The tensor couplings of vector mesons to baryons are included, and the change of baryon internal structure in matter is also considered using the quark-meson coupling model. We obtain the maximum neutron-star mass of $\sim 2.0 M_\odot$, which is consistent with the recently observed, precise mass, $1.97\pm0.04 M_{\odot}$. The Fock contribution is very important and, in particular, the inclusion of tensor coupling is vital to obtain such large mass. The baryon structure variation in matter also enhances the mass of a neutron star.

nucl-th↗