Heisenberg fields in the neighborhood of a classical solution

For the example of nonlinear models of a scalar field in two-dimensional space-time a study is made of a method of quantization in the neighborhood of a classical solution based on direct solution by perturbation theory of the Cauchy problem for the Heisenberg field equations. It is shown that, as in the classical Bogolyubov–Krylov method, zero modes and associated secular terms arise because of the perturbation-theory expansion of the Bogolyubov operator argument of the classical component. The Lehmann–Symanzik–Zimmermann procedure is used to make a complete investigation of the asymptotic states of the field in the soliton sector in the lowest orders of perturbation theory.