The study of nonstrange quark stars within a modified NJL model

Abstract

In this work, we employ a modified Nambu-Jona-Lasinio (NJL) model with proper-time regularization to study the structure of nonstrange quark stars. Considering the physical meaning of the four-fermion interaction coupling constant $G$ in the conventional NJL model, we modify it by $G=G_1+G_2\langle\bar{\psi}\psi\rangle$ to highlight the feedback of quark propagator to gluon propagator. To study the dependence of the equation of state (EOS) on this modification as well as the vacuum pressure, we choose nine representative EOSs for comparison. As a result, we find that a smaller $G_1$ corresponds to a stiffer EOS, but at low energy densities, a higher vacuum pressure (i.e., a smaller bag constant) yields a softer one. Furthermore, the heaviest quark star obtained with the modified NJL model satisfies not only recent mass measurement of PSR J0740+6620, but also radius constraints from x-ray timing observations. The corresponding tidal deformability is also in agreement with GW170817.Comment: 8 pages, 9 figure