Hawking radiation from Feynman diagrams

The aim of this paper is to clarify the relationships between Hawking radiation and the scattering of light by matter falling in a black hole. To this end we analyze the S-matrix elements of a model composed of a massive infalling particle (described by a quantized field) and the radiation field. These fields are coupled by current-current interactions and propagate in the Schwarzschild geometry. As long as the photons energy is much smaller than the mass of the infalling particle, one recovers Hawking radiation since, for large coupling, our S-matrix elements identically reproduce the usual Bogoliubov coefficients. However, after a brief period, when the energy of the “partners” of Hawking photons reaches this mass, the recoil effects stop the production of thermal photons through these interactions. The implications of this result are discussed.