Abstract
The Stuckelberg formalism for a massive spin-one field interacting with external potentials is quantized following the method of Takahashi and Umezawa. It is shown how the characteristic determinant of the field equations, which, in an earlier paper, was shown to have the same form as the Lee-yang determinant, for such a theory, determines the possibility of breakdown of Lorentz invariance in the procedure of the Takahashi-Umezawa quantization method.