Complex angular momentum in black hole physics and quasinormal modes

By using the complex angular momentum approach, we prove that the quasinormal-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 semiclassically the spectrum of the quasinormal-mode complex frequencies from Regge trajectories. The notion of a surface wave orbiting around black holes 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.