Nobel prize to S. Tomonaga awarded in 1965. Co-winners J. S. Schwinger and R. P. Feynman "for their fundamental work in quantum electrodynamics, with deep-ploughing consequences for the physics of elementary particles''
Koba, Z.; Tati, T.; Tomonaga, S.; On a Relativistically Invariant Formulation of the Quantum Theory of Wave Fields. III. Case of Interacting Electromagnetic and Electron Fields
Progr. of Theor. Phys. 2 (1947) 198;
We have thus shown that it is in fact possible to describe the behavior of the electromagnetic field interacting with electrons, in a perfectly relativistic form according to our general scheme developed in I. But if we wish to apply similar methods to more general cases, for instance, to the cases of the meson field interacting with the electromagnetic field or the nucleon field, some generalization is necessary. In fact, in the case of the quantum electrodynamics the situation is exceptionally
simple owing to the following two facts: (i) the interaction, energy density HI,II(P) is a scalar function of the fields and (ii) the integrability condition [HI,II(P),HI,II(P')] = 0 is satisfied from the beginning. These simplifying facts do no longer hold in the more general cases mentioned above. However, if some generalization of the formalism is made, it is possible to develop the similar theory also in these more complicated cases as will be
shown in the later paper. The development of such a theory seems to us of interest, not only because we obtain thus formally more satisfactory theory, but also because in this way we can hope that some new aspects of the difficulties underlying the current quantum theory of the fields would reveal itself. (Extracted from concluding remarks of the paper.).
Related references More (earlier) information appears in S. Tomonaga, Riken Iho 22 (1943) 525;
S. Tomonaga, Progr. of Theor. Phys. 1 (1946) 27;
Z. Koba, T. Tati, and S. Tomonaga, Progr. of Theor. Phys. 2 (1947) 101;
See also W. Heisenberg, Z. Phys. 110 (1938) 251;
T. Miyazima, Riken Iho 23 (1944) 27;
P. A. M. Dirac, V. A. Fock, and B. Podolsky, Physik Zeits. Sow. 2 (1932) 468;
Creation of the covariant quantum electrodynamic theory. Tomonaga method.