δ MESON EFFECTS ON NEUTRON STARS IN THE MODIFIED QUARK–MESON COUPLING MODEL

Abstract

The properties of neutron stars are investigated by including δ meson field in the modified quark–meson coupling model. It is found that δ meson has opposite effects on hadronic matter with or without hyperons: it softens the EOSs of hadronic matter with hyperons, while it stiffens the EOSs of pure nucleonic matter. Moreover, by replacing the isovector mesons with the contact scalar–isovector interaction, a considerable change of proton fraction is observed. It is shown that the contact scalar–isovector interaction provides an approach to satisfy the constraint of Direct Urca critical star masses. However, the inclusion of δ meson increases the proton fraction, consequently it decreases the M DU which departs farther from the Direct Urca constraint. Furthermore, the inclusion of δ meson field can increase the maximum mass of neutron star and enlarge the corresponding radius, while these quantities are decreased when the contact scalar–isovector interaction is included.