Abstract. Strong coupling between fermionic and bosonic degrees of freedom, highly anisotropic, nearly one dimensional character, asymmetry between stable and meta-stable phases are the most characteristic features incorporated into models of the photo-induced phase transitions. Searching for a unique, coherent approach treating these both types of degrees of freedom as dynamical variables we are arguing that a mean field type approximation for fermionic subsystem appears to be oversimplified; we propose here an approximation, which goes beyond mean field, but on the expense of a loosing nice interpretation of more naive Hartle-Fock approximation. Studying the properties of the bosonic, lattice subsystem, one can quantify asymmetry; in fact "large asymmetry" case is accompanied by the interesting phenomena like a sequence of (two) phase transformations, and (equilibrium) string formation. Equilibrium strings, domains of finite size of the opposite phase turns out to be present in vicinity of the transformation temperature.

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