18 research outputs found
Equation of State for Neutron Stars in the Quark-Meson Coupling Model with the Cloudy Bag
Using the quark-meson coupling model with the cloudy bag, we construct the
equation of state for neutron stars with hyperons in SU(3) flavor symmetry. The
hyperfine interaction due to the gluon exchange and the pion-cloud effect
inside a baryon is taken into account in vacuum and nuclear matter. We
investigate how the quark degrees of freedom and the exchanges of gluon and
pion between two quarks affect the properties of nuclear and neutron-star
matter. It is found that the variation of baryon substructure in matter plays
an important role in supporting massive neutron stars.Comment: 4 papes, 3 figures, 2 tables, accepted to the proceedings of the 8th
International Conference on Quarks and Nuclear Physics (QNP2018) in JPS
Conference Proceeding
Can the PREX-2 and CREX results be understood by relativistic mean-field models with the astrophysical constraints?
We construct new effective interactions using the relativistic mean-field
models with the isoscalar- and isovector-meson mixing,
and
. Taking into account
the particle flow data in heavy-ion collisions, the observed mass of PSR
J07406620, and the tidal deformability of a neutron star from binary merger
events, GW170817 and GW190814, we study the ground-state properties of finite,
closed-shell nuclei, and try to explain the recent results from the PREX-2 and
CREX experiments. It is found that the -- mixing is very
powerful to understand the terrestrial experiments and astrophysical
observations of neutron stars self-consistently. We can predict the large
neutron skin thickness of Pb, ~fm, using the
slope parameter of nuclear symmetry energy, ~MeV, which is consistent
with the PREX-2 result. However, to explain the CREX data, it is preferable to
adopt the small value of ~MeV. It is very difficult to understand the
PREX-2 and CREX results simultaneously within relativistic mean-field models.Comment: 7 pages, 6 figures, 4 table
Effects of neutron-rich nuclei masses on symmetry energy
We explore the impact of neutron-rich nuclei masses on the symmetry energy
properties using the mass table evaluated by the deformed relativistic
Hartree-Bogoliubov theory in continuum (DRHBc) model. First, using the
semi-empirical mass formula with the DRHBc mass table, we investigate the
symmetry energy at saturation density , denoted as , and the ratio
of surface to volume contributions to the symmetry energy, . As a
result, we obtain () for (Type I) and ()
for (Type II), which are
lower than those obtained using the AME2020 mass table,
() for Type I and () for Type
II. Second, we further investigate the effect of these changes in on the density-dependent symmetry energy by employing the empirical
model of and universal relation of . Compared to the experimental constraints, we find
that and slope parameter , determined by the DRHBc mass table with
Type II, are more suitable to explain the constraints by heavy ion collisions
and isobaric analog states than AME2020. We also discuss the neutron skin
thickness derived from the , comparing it with experimental measurements
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 fm, 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.Comment: 10 figures, 8 table