1. See, for instance,J. Weber:Symposium on Relativistic Astrophysics (Austin, Tex., 1970).
2. L. Halpern:Nature Phys. Sci.,223, 18 (1971).
3. D. Boccaletti, V. De Sabbata, P. Fortini andC. Gualdi:Nuovo Cimento,54 B, 134 (1968);Sov. Journ. Nucl. Phys.,8, 537 (1969);L. Halpern andB. Laurent:Nuovo Cimento,33, 728 (1964).
4. G. M. Gandel'man andV. S. Pinaev:Sov. Phys. JETP,10, 764 (1959);S. Weinberg:Phys. Rev.,140, B 516 (1965);M. Carmeli:Phys. Rev.,158, 1243 (1967).
5. S. Tsuruta, V. Canuto, J. Lodenquai andM. Ruderman: G.S.F.C. preprint;