Pion condensation in a soft-wall AdS/QCD model

Finite isospin chemical potential $\mu_I$ and temperature $T$ have been introduced in the framework of soft-wall AdS/QCD model. By self-consistently solve the equation of motion, we obtain the phase boundary of pion condensation phase, across which the system undergoes a phase transition between pion condensation phase and normal phase. Comparing the free energy of solutions with and without pion condensation, we find that the phase transition is of first order type both at large $\mu_I$ and small $\mu_I$. Qualitatively, the behavior at large $\mu_I$ is in agreement with the lattice simulation in Phys.Rev.D66(2002)034505, while the behavior at small $\mu_I$ is different from lattice simulations and previous studies in hard wall AdS/QCD model. This indicates that a full back-reaction model including the interaction of gluo-dynamics and chiral dynamics might be necessary to describe the small $\mu_I$ pion condensation phase. This study could provide certain clues to build a more realistic holographic model.