Quasinormal resonances of a charged scalar field in a charged   Reissner-Nordstr\"om black hole spacetime: A WKB analysis
  The fundamental quasinormal resonances of charged Reissner-Nordstr\"om black holes due to charged scalar perturbations are derived {\it analytically}. In the WKB regime, $qQ\gg\hbar$, we obtain a simple expression for the fundamental quasinormal resonances: $\omega=qQ/r_+-i2\pi T_{\text{BH}}(n+{1 \over 2})$, where $T_{\text{BH}}$ and $Q$ are the temperature and electric charge of the black hole and $q$ is the electric charge of the field. Remarkably, our results show that the relaxation dynamics of a perturbed Reissner-Nordstr\"om black hole may saturate the recently proposed universal relaxation bound. 
Shahar Hod
gr-qc astro-ph.HE hep-th