Neutron star matter with Δ isobars in a relativistic quark model

The possibility of the appearance of Delta(1232) isobars in neutron star matter and the so-called Delta puzzle is investigated in a relativistic quark model where the confining interaction for quarks inside a baryon is represented by a phenomenological average potential in an equally mixed scalar-vector harmonic form. The hadron-hadron interaction in nuclear matter is then realized by introducing additional quark couplings to sigma, omega, and rho mesons through mean-field approximations. The hyperon couplings are fixed from the hyperon optical potentials at saturation density. Effects of moderate variations in the Delta-omega and Delta-rho coupling strengths on the critical density of forming Delta resonances and on the mass-radius relation of neutron stars is studied. We have also made an attempt to study the impact of in-medium mass variations of the Delta baryon on the structure of neutron stars. It is observed that, within the constraints of the masses of the precisely measured massive pulsars PSR J0348+0432 and PSR J1614-2230, neutron stars with a composition of both Delta isobars and hyperons are possible in the present model.