Superradiant instability in slowly rotating Kerr-Newman black holes

In this paper, we study the superradiant instability of slowly rotating Kerr-Newman (sKN) black holes under a charged massive scalar perturbation. These black holes resemble closer the Reissner-Nordstrom black holes than the Kerr-Newman black holes. From the scalar potential analysis, we find that the superradiant instability is not allowed in the sKN black holes because the condition for a trapping well is not compatible with the superradiance condition. However, the rate of energy extraction might grow exponentially if the sKN black hole is placed inside a reflecting cavity. Finally, we obtain two conditions for the trapping well to possess quasibound states in the sKN black holes by analyzing asymptotic scalar potential and far-region wave functions.