1. This chapter takes again the ideas and the results previously published in: A. Julg, Ann. Fond. Louis de Broglie
16 (1991) 321 and
2. A. Julg in Waves and Particles in Light and Matter, A. van der Merwe and A. Garuccio eds (Plenum, New York) 1994, p.337, with some modifications and supplementary details.
3. L. Landau, F. Lifchitz, Physique Théorique II (Théorie des champs), (Mir, Moscou) 3ème éd. 1970, p. 280.
4. J.D. Jackson, Classical Electrodynamics (Wiley, New York) 2th ed., 1975, p.560.
5. L. Nottale, in Quantum Mechanics, diffusion and chaotic fractals, M.El Nashie, O. Rössler, I. Prigogine Eds. (Pergamon Press, New York) 1995 and references therein.