On Evolution Equations for Marginal Correlation Operators
  This paper is devoted to the problem of the description of nonequilibrium correlations in quantum many-particle systems. The nonlinear quantum BBGKY hierarchy for marginal correlation operators is rigorously derived from the von Neumann hierarchy for correlation operators that give an alternative approach to the description of states in comparison with the density operators. A nonperturbative solution of the Cauchy problem of the nonlinear quantum BBGKY hierarchy for marginal correlation operators is constructed. 
V.I. Gerasimenko, D.O. Polishchuk
math-ph cond-mat.stat-mech math.AP math.MP quant-ph