1. É. A. Tagirov and N. A. Chernikov, Preprint No. 2-3777, OIYaI (Joint Institute for Nuclear Research, Dubna, 1968); K. A. Bronnikov and É. A. Tagirov, Preprint No. 2-4151, OIYaI (Joint Institute for Nuclear Research, Dubna, 1968).
2. G. L. Parker, Phys. Rev. Lett. 21, 562 (1968);
3. Phys. Rev. 183, 1057 (1969);
4. Phys. Rev. D 3, 346 (1971).
5. A. A. Grib and S. G. Mamaev, Yad. Fiz. 10, 1276 (1969) [Sov. J. Nucl. Phys. 10, 722 (1970)].