Density matrix interpretation of solutions of Lie-Nambu equations

The spectrum of a density matrix rho(t) is conserved by the Lie-Nambu dynamics if rho(t) is a self-adjoint and Hilbert-Schmidt solution of a nonlinear triple-bracket equation. This generalizes the previous result, which was valid for finite-dimensional Hilbert spaces, to arbitrary separable (positive-and indefinite-metric) Hilbert spaces. (C) 1998 Elsevier Science B.V.