LQCD constrained magnetic field dependent coupling constant in an effective model

Abstract: A magnetic field dependent coupling constant $G(eB)$ is investigated in the two-flavor magnetized NJL model. Based on LQCD results of the neutral (charged) pion mass spectra at vanishing temperature and finite magnetic field, we determine the $G(eB)=G^0(eB)$ ($G(eB)=G^+(eB)$) in the NJL model. $G^0(eB)$ and $G^+(eB)$ are both non-monotonic functions of magnetic fields, but they are different from each other. Furthermore, we calculate the pseudo-critical temperatures $T_{pc}(eB)$ of chiral restoration phase transition with $G^0(eB)$ and $G^+(eB)$ in the magnetized NJL model, respectively. The resulting $T_{pc}(eB)$ are non-monotonic functions of magnetic fields. In previous work, $G(eB)$ in the NJL model fitted from the chiral condensate or pseudo-critical temperature of LQCD simulations is a decreasing function of magnetic field. It can not explain the saturation behavior of mass spectra of neutral pion and decreasing behavior of mass spectra of charged pion with strong magnetic field. We conclude that a magnetic field dependent coupling constant $G(eB)$ in the NJL model can not simultaneously explain the reduction of pseudo-critical temperature of chiral restoration phase transition and the light meson mass spectra under external magnetic field.