Chiral phase transition and spin alignment of vector mesons with chiral imbalance in a rotating QCD medium

Abstract

We study the two-flavor NJL model under the rotation and chiral chemical potential $\mu_{5}$. Firstly, the influence of chiral imbalance on the chiral phase transition in the $T_{pc}-\omega$ plane is investigated. Research manifests that as $\mu_{5}$ increases, the critical point (CEP) of the $T_{pc}-\omega$ plane chiral phase transition will move closer to the $T$ axis. This means that the chiral chemical potential $\mu_{5}$ can significantly affect the $T_{pc}-\omega$ phase diagram and phase transition behavior. While discussing the $T_{pc}-\omega$ phase diagram, we also study the spin alignment of the $\rho$ vector meson under rotation. In the study of the spin alignment of the vector meson $\rho$, $\rho_{00}$ is the $00$ element of the spin density matrix of vector mesons. At high temperatures, $\rho_{00}$ is close to $1/3$, it indicates that the spin alignment of the vector meson $\rho$ is isotropic. It is found that increasing the chiral chemical potential $\mu_{5}$ significantly enhances $\rho_{00}$, and makes $\rho_{00}$ approaching to $1/3$ around the phase transition temperature. When rotational angular velocity is zero, $\rho_{00}$ is close to $1/3$, but as $\omega$ increases, $\rho_{00}$ significantly decreases, and deviates $1/3$, indicating that rotation can significantly cause polarization characteristics. The $\rho_{00}-r$ relationship near the phase transition temperature is studied. It is found that the farther away from the center of rotation, the lower the degree of spin polarization of the system. It is also found that the influence of chiral imbalance on the $\rho_{00}-r$ relationship is also significant.