LEPTON PAIR PRODUCTION BY A HIGH-ENERGY PHOTON IN A STRONG ELECTROMAGNETIC-FIELD

Using the impact-factor representation, we consider lepton pair produc tion by an incident high energy photon in the strong electromagnetic f ield of a nucleus. By summing leading terms of the perturbation series , we obtain a simple formula for the amplitude, valid to all orders in O(alpha Z) and an arbitrary field of the nucleus. Using these results , we derive, in a simple manner, the results for lepton pair productio n by a virtual incident photon in a Coulomb field. For a real incident photon our results coincide with the known ones. Also, a particular e xample of a non-Coulomb potential is discussed in some detail. [S0556- 2821(98)02307-8].