  Many-body interactions in effective field theories for disordered interacting
electrons are considered. It is shown that three-body and higher interaction
terms are generated in perturbation theory, and some of the physical
consequences of these interactions are discussed. It is shown in particular
that they will in general be important for any effects governed by
strong-coupling fixed points. This implies that the usual generalized nonlinear
sigma-model for disordered electron systems is incomplete, and not suitable for
studying strong-coupling effects.
