ABSORPTION OF PHOTONS AND FERMIONS BY BLACK-HOLES IN 4 DIMENSIONS

The absorption of photons and fermions into four-dimensional black hol es is described by equations which in certain cases can be analyzed us ing dyadic index techniques. The resulting absorption cross sections f or near-external black holes have a form at low energies suggestive of the effective string model. A coupling to the effective string is pro posed for spin-0 and spin-1/2 fields of pure N=4 supergravity which re spects the unbroken supersymmetry of extreme black holes and correctly predicts dilaton, axion, and fermion cross sections up to an overall normalization. [S0556-2821(97)04124-6].