Topological susceptibility and axion properties in the presence of a strong magnetic field within the three-flavor NJL model

Abstract

We analyze the topological susceptibility and the axion properties in the presence of an external uniform magnetic field, considering a three-flavor Nambu-Jona-Lasinio model that includes strong 𝐶𝑃 violation through a ’t Hooft-like flavor mixing term. Both thermal and finite density effects are studied for magnetic fields up to 1GeV^2, and the corresponding phase transitions are analyzed. To capture the inverse magnetic catalysis effect at finite temperatures and densities, a magnetic-field-dependent coupling constant is considered. Our analytical and numerical results are compared with those previously obtained from lattice QCD, chiral perturbation theory, and other effective models.