1. For a general discussion of the application ofS-matrix theory to electromagnetic interactions seeA. O. Barut:S-Matrix Theory of Electromagnetic Interactions, to be published in theProceedings of the Schladming Conference on Electrodynamics (1965).
2. See, for example,J. M. Jauch andF. Rohrlich:The Theory of Photons and Electrons (Cambridge, Mass., 1955), p. 229.
3. See, for example,J. M. Jauch andF. Rohrlich:The Theory of Photons and Electrons (Cambridge, Mass., 1955).
4. Similar integrals have beenal ready calculated byKällén, seee.g.,G. A. O. Källén: inElementary-Particle Physics and Field Theory,K. W. Ford, editor (New York, 1961).