Dynamical susceptibilities in a strong coupling approach

A general scheme to calculate dynamical susceptibilities of strongly correlated electron systems within the dynamical mean field theory is developed. The approach is based on an expansion over electron hopping around the atomic limit (within the diagrammatic technique for site operators: projection and Hubbard ones) in infinite dimensions. As an example, the Falicov-Kimball and simplified pseudospin-electron models are considered and analytical expressions for the dynamical susceptibilities are obtained.