Dynamics-generating semigroups and phenomenology of decoherence

The earlier proposed Dynamics-Generating Approach (DGA) is reviewed and extended. Starting from an arbitrary chosen group or semigroup having structure similar to the structure of Galilei group, DGA allows one to construct phenomenological description of dynamics of the corresponding "elementary quantum object" (a particle or non-local object of special type). A class of Galilei-type semigroup, with semigroup of trajectories (parametrized paths) instead of translations, allows to derive, in the framework of DGA, Feynman path integrals. The measure of path integrating (exponential of the classic action) is not postulated but derived from the structure of projective semigroup representations. The generalization of DGA suggested in the present paper allows one to derive dynamics of open quantum systems. Specifically, phenomenological description of decoherence and dissipation of a non-relativistic particle is derived from Galilei semigroup.