General susceptibilities of highly correlated electron systems from a local point of view

We present Bethe-Salpeter equations derived via a cumulant expansion in terms of the transfer between lattice sites in the presence of large local Coulomb-matrix elements. Using only local irreducible vertices as in the dynamical mean field theory, general susceptibilities can be approximated. Employing a decoupling scheme for the energy summations, we obtain a typical Stoner form, in which the non-local interaction part is explicitly known. (c) 2005 Published by Elsevier B.V.