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 $M_\odot$. 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$_\odot$, with central density less than 6 times nuclear saturation density ($n_{0}= 0.16 {\rm fm}^{-3}$) 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 $3n_0$, for matter in $\beta$-equilibrium. At higher densities, $\Xi^{-,0}$ and $\Lambda$ 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 $^{16}$O to $^{208}$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

γ-Ray linear polarization measurements on oriented nuclei

The present status of γ-ray linear polarization measurements on oriented nuclei is discussed. The formalism used in the analysis of experimental data is summarized and complemented by formulae for γ-transitions with triple multipole mixing. A survey of the present technique of detection of γ-ray linear polarization, using Compton polarimeters, is given. Two important applications of γ-ray linear polarization measurements are briefly surveyed, namely, the measurement of the g-factors excited states and the investigation of time-reversal symmetry in atomic nuclei. © 1985 J.C. Baltzer A.G., Scientific Publishing Company

Electric monopole transitions and isotope shift of nuclear radii of even Sm isotopes in the interacting boson model

The interacting boson model has been used to calculate the isotope shift in146-154Sm isotopes. Fitted model parameters have been used for calculation of the monopole strength parameters ρ(EO) and the branching ratios X(EO/E2) for150-154Sm. Consideration of the effective proton boson number as it reflects the Z=64 subshell closure, is shown to be insignificant in the present calculation. © 1987 J.C. Baltzer A.G., Scientific Publishing Company