Complex angular momenta and the black-hole glory

Numerical calculations relevant for a complex angular momentum (CAM) description of black-hole scattering have been performed for the first time. The study concerns the relatively simple case of monochromatic scalar waves scattered off a Schwarzschild black hole, but the approach can easily be generalized to more complicated situations. The interpretative power of the CAM representation is discussed and is found to be very appealing: all features of the black-hole scattering cross sections can be understood in terms of interference between a few surface waves (represented by a sum over the so-called Regge poles) and a single optical ray (a smooth background integral). In a specific example we show that only one Regge pole is needed to describe the glory oscillations that occur for large scattering angles.