1. L.D. Landau, E.M. Lifshits, Quantum Mechanics. Nonrelativistic Theory (Pergamon, N.Y., 1977)
2. J.D. Bjorken, S.D. Drell, Relativistic Quantum Mechanics (McGraw-Hill Book Company, 1964)
3. V.B. Berestetskii, E.M. Lifshits, L.P. Pitaevskii, Quantum Electrodynamics (Pergamon, N.Y., 1982)
4. V.G. Gorshkov, S.G. Sherman, JETP Lett. 17, 374 (1973)
5. E.G. Drukarev, V.G. Gorshkov, A.I. Mikhailov, S.G. Sherman, Phys. Lett. A 46, 467 (1974)