Properties of the phase diagram from the Nambu-Jona-Lasino model with a scalar-vector interaction

We investigated the properties of the phase diagram of high-order susceptibilities, speed of sound, and polytropic index based on an extended Nambu-Jona-Lasinio model with an eight-quark scalar-vector interaction. Non-monotonic behavior was observed in all these quantities around the phase transition boundary, which also revealed the properties of the critical point. Further, this study indicated that the chiral phase transition boundary and critical point could vary depending on the scalar-vector coupling constant \(G_\text {SV}\). At finite densities and temperatures, the negative \(G_\text {SV}\) term exhibited attractive interactions, which enhanced the critical point temperature and reduced the chemical potential. The \(G_\text {SV}\) term also affected the properties of the high-order susceptibilities, speed of sound, and polytropic index near the critical point. The non-monotonic (peak or dip) structures of these quantities shifted to a low baryon chemical potential (and high temperature) with a negative \(G_\text {SV}\). \(G_\text {SV}\) also changed the amplitude and range of the nonmonotonic regions. Therefore, the scalar-vector interaction was useful for locating the phase boundary and critical point in QCD phase diagram by comparing the experimental data. The study of the non-monotonic behavior of high-order susceptibilities, speed of sound, and polytropic index is of great interest, and further observations related to high-order susceptibilities, speed of sound, and polytropic index being found and applied to the search for critical points in heavy-ion collisions and the study of compact stars are eagerly awaited.