The quantum electrodynamics (QED) of electrons is considered as a theory with a passive dilatation invariance which is perturbed by the electromagnetic coupling to hadrons and muons. A stability criterium is introduced and evaluated in lowest order of the perturbation. The resulting expression for the electron-muon mass ratio in terms of the vacuum polarization can be tested in e+ − e− colliding beam experiments.
Nuclear Physics B. Amsterdam. Vol. 88, no. 2 (Mar. 1975), p. 337-348