  The dynamical map represents a fundamental concept in quantum field theory,
providing a solution of the field equations in the Fock space of asymptotic
fields. In this paper, we show how to express the dynamical map of a scalar
field in the language of quantum effective action. This grants us new insights
into the study of topological defects in quantum field theory, showing a
connection between the usual least-action principle and Umezawa's boson
transformation method.
