1. F. R. Tangheruni:Ann. N.Y. Acad. Sci.,422, 385 (1984).
2. A. Einstein:The Meaning of Relativity, Appendix II, 5th edition, translated byS. Bargmann (Princeton University Press, Princeton, N.J., 1955), p. 164.
3. E. A. Milne:Quart. J. Math. (Oxford Ser.),5, 64 (1934);W. H. McCrea andE. A. Milne:quart. J. Math. (Oxford Ser.),5, 73 (1934).
4. P. Fayet:Phys. Lett. B,69, 489 (1977).
5. E. W. Kolb andM. S. Turner:The Early Universe (Addison-Wesley, Reading, Mass., 1990).