We define a sequence of microscopic dynamical variables by decomposing a Hilbert space into orthogonal subspaces, and construct for them a new hierarchy of equations which is particularly useful for highly correlated systems. A formal solution is shown to give a microscopic expression of Mori's...

Collisions between atoms through the intermediary of zero sound wave of finite lifetimes are discussed to account for the memory effect on the density correlations of atoms. The second-quantization formalism is used to describe the formation and decay of zero sound, and a new non-markovian...

A new formula for the binary collision expansion of the unitary operator U (t2, t1) is proposed. The formula is applied to the expansion of the partial Green's functions of Kadanoff-Baym in powers of the correct binary scattering amplitude. It is shown that certain linked diagrams of...