Quantization of lorentz-invariant systems in terms of bogolyubov group variables. II: Construction of perturbation theory

For $(3+1)$-dimensional systems invariant under transformations that form a Poincare group, the Bogolyubov group variables are defined. This makes it possible to carry out quantization near a time-dependent classical scalar field. The constants of motion and the field operators are found to within the zeroth order in reciprocal powers of the coupling constant.