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Register a new userKaon condensation in the quark-meson coupling model and compact stars
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The properties of neutron stars constituted of a crust of hadrons and an internal part of hadrons and kaon condensate are calculated within the quark-meson-coupling model. We have considered stars with nucleons only in the hadron phase and also stars with hyperons as well. The results are compared with the ones obtained from the non-linear Walecka model for the hadronic phase.
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Assuming that at sufficiently high densities the constituent quarks become relevant degrees of freedom, we study within the framework of a chiral quark model the influence of s-wave $K^-$ condensation on the quark-antiquark condensates. We find that, in linear density approximation, the presence of a $K^-$ condensate quenches the $bar{u}u$ condensate, but that the $bar{d}d$ condensate remains unaffected up to the chiral order under consideration. We discuss the implication of the suppressed $bar{u}u$ condensate for flavor-dependent chiral symmetry restoration in dense matter
The recent observations of the massive pulsars PSR J1614-2230 and of PSR J0348+0432 with about two solar masses implies strong constraints on the properties of dense matter in the core of compact stars. Effective models of QCD aiming to describe neutron star matter can thereby be considerably constrained. In this context, a chiral quark-meson model based on a SU(3) linear $sigma$-model with a vacuum pressure and vector meson exchange is discussed in this work. The impact of its various terms and parameters on the equation of state and the maximum mass of compact stars are delineated to check whether pure quark stars with two solar masses are feasible within this approach. Large vector meson coupling constant and a small vacuum pressure allow for maximum masses of two or more solar masses. However, pure quark stars made of absolutely stable strange quark matter, so called strange stars, turn out to be restricted to a quite small parameter range.
In-medium properties of the low-lying baryons are studied in the quark-meson coupling (QMC) model, focusing on the $Sigma_b$ and $Xi_b$ baryons. It is predicted that the Lorentz-scalar effective mass of $Sigma_b$ becomes smaller than that of $Xi_b$ at moderate nuclear matter density, and as the density increases, namely, $m^*_{Sigma_b} < m^*_{Xi_b}$, although in vacuum $m_{Sigma_b} > m_{Xi_b}$. We also study the effects of the repulsive Lorentz-vector potentials on the excitation energies of these bottom baryons.
In-medium properties of the low-lying strange, charm, and bottom baryons in symmetric nuclear matter are studied in the quark-meson coupling (QMC) model. Results for the Lorentz-scalar effective masses, mean field potentials felt by the light quarks in the baryons, in-medium bag radii, and the lowest mode bag eigenvalues are presented for those calculated using the updated data. This study completes the in-medium properties of the low-lying baryons in symmetric nuclear matter in the QMC model, for the strange, charm and bottom baryons which contain one or two strange, one charm or one bottom quarks, as well as at least one light quark. Highlight is the prediction of the bottom baryon Lorentz-scalar effective masses, namely, the Lorentz-scalar effective mass of $Sigma_b$ becomes smaller than that of $Xi_b$ at moderate nuclear matter density, $m^*_{Sigma_b} < m^*_{Xi_b}$, although in vacuum $m_{Sigma_b} > m_{Xi_b}$. We study further the effects of the repulsive Lorentz-vector potentials on the excitation (total) energies of these bottom baryons.
We present a selection of the first results obtained in a comprehensive calculation of ground state properties of even-even superheavy nuclei in the region of 96 < Z < 136 and 118 < N < 320 from the Quark-Meson-Coupling model (QMC). Ground state binding energies, the neutron and proton number dependence of quadrupole deformations and Q$_alpha$ values are reported for even-even nuclei with 100 < Z < 136 and compared with available experimental data and predictions of macro-microscopic models. Predictions of properties of nuclei, including Q$_alpha$ values, relevant for planning future experiments are presented.
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