139 research outputs found
Cold uniform matter and neutron stars in the quark-mesons-coupling model
A new density dependent effective baryon-baryon interaction has been recently
derived from the quark-meson-coupling (QMC) model, offering impressive results
in application to finite nuclei and dense baryon matter. This self-consistent,
relativistic quark-level approach is used to construct the Equation of State
(EoS) and to calculate key properties of high density matter and cold, slowly
rotating neutron stars. The results include predictions for the maximum mass of
neutron star models, together with the corresponding radius and central
density, as well the properties of neutron stars with mass of order 1.4
. The cooling mechanism allowed by the QMC EoS is explored and the
parameters relevant to slow rotation, namely the moment of inertia and the
period of rotation investigated. The results of the calculation, which are
found to be in good agreement with available observational data, are compared
with the predictions of more traditional EoS. The QMC EoS provides cold neutron
star models with maximum mass 1.9--2.1 M, with central density less
than 6 times nuclear saturation density () and
offers a consistent description of the stellar mass up to this density limit.
In contrast with other models, QMC predicts no hyperon contribution at
densities lower than , for matter in -equilibrium. At higher
densities, and hyperons are present
Microscopic calculation of the equation of state of nuclear matter and neutron star structure
We present results for neutron star models constructed with a new equation of
state for nuclear matter at zero temperature. The ground state is computed
using the Auxiliary Field Diffusion Monte Carlo (AFDMC) technique, with
nucleons interacting via a semi-phenomenological Hamiltonian including a
realistic two-body interaction. The effect of many-body forces is included by
means of additional density-dependent terms in the Hamiltonian. In this letter
we compare the properties of the resulting neutron-star models with those
obtained using other nuclear Hamiltonians, focusing on the relations between
mass and radius, and between the gravitational mass and the baryon number.Comment: modified version with a slightly different Hamiltonian and
parametrization of the EO
Hyperons and massive neutron stars: the role of hyperon potentials
The constituents of cold dense matter are still far from being understood.
However, neutron star observations such as the recently observed pulsar PSR
J1614-2230 with a mass of 1.97+/-0.04 M_solar help to considerably constrain
the hadronic equation of state (EoS). We systematically investigate the
influence of the hyperon potentials on the stiffness of the EoS. We find that
they have but little influence on the maximum mass compared to the inclusion of
an additional vector meson mediating repulsive interaction amongst hyperons.
The new mass limit can only be reached with this additional meson regardless of
the hyperon potentials. Further, we investigate the impact of the nuclear
compression modulus and the effective mass of the nucleon at saturation density
on the high density regime of the EoS. We show that the maximum mass of purely
nucleonic stars is very sensitive to the effective nucleon mass but only very
little to the compression modulus.Comment: 24 pages, 8 figure
Phase transition to the state with nonzero average helicity in dense neutron matter
The possibility of the appearance of the states with a nonzero average
helicity in neutron matter is studied in the model with the Skyrme effective
interaction. By providing the analysis of the self-consistent equations at zero
temperature, it is shown that neutron matter with the Skyrme BSk18 effective
force undergoes at high densities a phase transition to the state in which the
degeneracy with respect to helicity of neutrons is spontaneously removed.Comment: 4 pages, 3 figures; v2: journal versio
Many-body perturbation calculation of spherical nuclei with a separable monopole interaction: I. Finite nuclei
We present calculations of ground state properties of spherical, doubly
closed-shell nuclei from O to Pb employing the techniques of
many-body perturbation theory using a separable density dependent monopole
interaction. The model gives results in Hartree-Fock order which are of similar
quality to other effective density-dependent interactions. In addition, second
and third order perturbation corrections to the binding energy are calculated
and are found to contribute small, but non-negligible corrections beyond the
mean-field result. The perturbation series converges quickly, suggesting that
this method may be used to calculate fully correlated wavefunctions with only
second or third order perturbation theory. We discuss the quality of the
results and suggest possible methods of improvement.Comment: 20 Pages, 11 figure
Quark deconfinement in nuclei: A review of experimental tests based on nuclear magnetic moment measurements
The introduction very briefly outlines the basic idea and experimental evidence to suggest that quarks may behave differently in nuclei and in indididual nucleons, with possible consequences for the calculation of nuclear magnetic dipole moments. After description of a calculation of moments made using the extreme model of total quark deconfinement (the MIT bag model) attention is focussed on experimental tests and the state of current evidence for more partial quark deconfinement. The arguments of Yamazaki which give an experimental basis for distinguishing quark deconfinement effects from, specifically, effects caused by pion echange currents, are given in more detail. The reasons underlying choice of nuclei in which meaningful tests may be possible are given. Early claims by Karl et al. to have demonstrated the existence of quark deconfinement in mass 3 nuclei are discussed. The current status of evidence for deconfinement based on orbital gfactor measurements in heavier nuclei is also summarised. Finally some examples are given of possible experiments using recently developed on-line facilities which may provide further tests of these ideas. © 1998 J.C. Baltzer A.G., Scientific Publishing Company
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