The structure of operators in effective particle-conserving models

摘要: For many-particle systems defined on lattices we investigate the global structure of effective Hamiltonians and observables obtained by means a suitable basis transformation. We study transformations which lead to conserving number excitations. The same transformation must be used obtain observables. analysis shows that operators give rise simple intuitive perspective initial problem. systematic calculation n-particle irreducible quantities becomes possible constituting significant progress. Details how implement approach perturbatively for large class are presented.