In the notation ofJ. D. Bjorken andS. D. Drell:Relativistic Quantum Mechanics (New Yor, N. Y., 1964).
See for that matterW. Wessel andS. J. Czyzak:Phys. Rev.,91, 986 (1953). and the report of the author:Fortschr. Phys.,12, 409 (1964) as well as the work of Bopp and Hönl and others, reviewed byH. Hönl:Ergebn. exact. Naturw.,26, 291 (1952). The point is that a charged particle in interaction with its own field may classically be described by a four-momentum and a four-velocity as independent variables. The latter acts like an inner variable that survives in the system of vanishing momentum.
W. Weissel:Nuovo Cimento,13 A, 248 (1973), to be quoted henceforth as I.
I. T. Grodsky andR. F. Streater:Phys. Rev. Lett.,20, 695 (1968).
A. O. Barut andJ. Nagel:J. Phys. A,10, 1233 (1977).
W. Wessel:Zeits. Phys.,206, 471 (1967).
The author owes this insight to a kind letter ofW. Rühl.
A. O. Barut:Phys. Rev.,135, B 839 (1964).
J. M. Gelfand, R. A. Minlos andZ. Ya. Shapiro:Representations of the Rotation and Lorentz Groups and their Applications (London, 1963).
A. Chakrabarti, M. Levy-Nahas andR. Seneor:Journ. Math. Phys.,9, 1274 (1968).
The general form is [II(σ+iK) II(σ−iK)]1/2 times a polynomial inK. Explicit solutions are givenPhys. Rev.,83, 1031 (1951) and in a condensed, but nonnormalized form in I, formula (2.2).
E. Majorana:Nuovo Cimento,9, 335 (1932).
H. Meschkowski:Differenzengleichungen (Göttingen, 1959).