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 1  GeV2, 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. Published by the American Physical Society 2025