Magnetic susceptibility of a strongly interacting thermal medium with 2+1 quark flavors

Thermodynamics of the three-flavor quark-meson model with UA(1) anomaly is studied in the presence of external magnetic fields. The nonperturbative functional renormalization group is employed in order to incorporate quantum and thermal fluctuations beyond the mean-field approximation. We calculate the magnetic susceptibility with proper renormalization and find that the system is diamagnetic in the hadron phase and paramagnetic in the hot plasma phase. The obtained values of the magnetic susceptibility are in reasonable agreement with the data from first-principle lattice QCD. Comparison with the mean-field approximation, the Hadron Resonance Gas model and a free gas with temperature-dependent masses is also made.