Quantum processes in an intense electromagnetic field. I

The Furry approach for arbitrary external electromagnetic fields that do not generate real pairs is considered. Problems of the existence of a stable vacuum in the field are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 81–86, October, 1976.The author is grateful to F. A. Berezin for refinement of the theorems used in this work and to A. A. Grib, S. G. Mamaev, and V. M. Mostepanenko for valuable critical comments.