Complex angular momentum in black hole physics and the quasi-normal modes

By using the complex angular momentum approach, we prove that the quasi-normal mode complex frequencies of the Schwarzschild black hole are Breit-Wigner type resonances generated by a family of surface waves propagating close to the unstable circular photon (graviton) orbit at $r=3M$. Furthermore, because each surface wave is associated with a given Regge pole of the $S$-matrix, we can construct the spectrum of the quasinormal-mode complex frequencies from Regge trajectories. The notion of surface wave orbiting around a black hole thus appears as a fundamental concept which could be profitably introduced in various areas of black hole physics in connection with the complex angular momentum approach.