On time-dependent projectors and on generalization of thermodynamical approach to open quantum systems

Abstract: In this paper, we develop a consistent perturbative technique for obtaining a time-local master equation based on projective methods in the case where the projector depends on time. We then introduce a generalization of the Kawasaki--Gunton projector, which allows us to use this technique to derive, generally speaking, nonlinear master equations in the case of arbitrary ansatzes consistent with some set of observables. Most of our results are very general, but in our discussion we focus on the application of these results to the theory of open quantum systems.