QCD phase diagram at finite isospin and baryon chemical potentials with the self-consistent mean field approximation
The self-consistent mean field approximation of two-flavor NJL model with introducing a free parameter $α$ to reflect the competition between "direct" channel and the "exchange" channel, is employed to study QCD phase structure at finite isospin chemical potential $μ_I$, finite baryon chemical potential $μ_B$ and finite temperature $T$, especially the location of the QCD critical point. It is found that, for fixed isospin chemical potentials the lower temperature of phase transition is obtained with $α$ increasing in the $T-μ_I$ plane, and the largest difference of the phase transition temperature with different $α$'s appears at $μ_I \sim 1.5m_π$. At $μ_I=0$ the temperature of the QCD critical end point (CEP) decreases with $α$ increasing, while the critical baryon chemical potential increases. At high isospin chemical potential ($μ_I=500$ MeV), the temperature of the QCD tricritical point (TCP) increases with $α$ increasing, and in the regions of low temperature the system will transit from pion superfluidity phase to the normal phase as $μ_B$ increases. At low temperatures, the critical temperature of QCD phase transition with different $α$'s rapidly increases with $μ_I$ at the beginning, and then increases smoothly around $μ_I>300$ MeV. In high baryon density region, the increase of the isospin chemical potential will raise the critical baryon chemical potential of phase transition.