1. C. Rebbi,Phys. Rep. C 12 (1974), Sec. 2, especially pp. 14–17 and Eqs. (2.78) and (2.79). J. Scherk,Rev. Mod. Phys. 47, 123–164 (1975);
2. B. M. Barbashov and V. V. Nesterenko,Sov. J. Part. Nucl. 9(5) (1978).
3. F. Rohrlich,Phys. Rev. Lett. 34, 842 (1975);Nucl. Phys. B 112, 177 (1976).
4. F. Rohrlich,Nuovo Cimento A 37, 242 (1977).
5. P. H. Frampton,Phys. Rev. D 12, 538 (1975).