Properties of strange quark matter and a quark star with axion interactions within an SU(3) Nambu–Jona-Lasinio model

We investigate the properties of quark matter and quark stars (QSs) within the SU(3) Nambu-Jona-Lasinio model, considering the effects of axion fields and vector interactions. Under the assumption of the absolutely stable condition of strange quark matter, we find that including axion effects and vector interactions significantly influences the equation of state, constituent quark mass, isospin asymmetry for $u$ and $d$ quarks, quark fractions, sound velocity, and the maximum mass of QSs. In particular, our results indicate that the central baryon density of the maximum star mass and the polytropic index $\ensuremath{\gamma}$ both decrease with increasing star mass, and we can describe the recently observed extremely large pulsars as QSs using absolutely stable strange quark matter.