Quark magnetar in the three-flavor Nambu–Jona-Lasinio model with vector interactions and a magnetized gluon potential

Abstract

We investigate properties of strange quark matter in the framework of the SU(3) Nambu--Jona-Lasinio model with vector interactions under strong magnetic fields. The effects of vector-isoscalar and vector-isovector interactions on the equation of state of strange quark matter are investigated, and it is found that the equation of state is not sensitive to the vector-isovector interaction; however, a repulsive interaction in the vector-isoscalar channel gives a stiffer equation of state for cold dense quark matter. In the presence of a magnetic field, gluons will be magnetized via quark loops, and the contribution from magnetized gluons to the equation of state is also estimated. The sound velocity square is a quantity to measure the hardness or softness of dense quark matter, and in the Nambu--Jona-Lasinio model without vector interaction at zero magnetic field, the sound velocity square is always less than $1/3$. It is found that a repulsive vector-isoscalar interaction and a positive pressure contribution from magnetized gluons can enhance the sound velocity square, which can even reach 1. To construct quark magnetars under strong magnetic fields, we consider anisotropic pressures and use a density-dependent magnetic field profile to mimic the magnetic field distribution in a quark star. We also analyze the parameter region for the magnitude of vector-isoscalar interaction and the contribution from magnetized gluons in order to produce two-solar-mass quark magnetars.