  Unstable four-boson states having an approximate dimer-atom-atom structure
are studied using momentum-space integral equations for the four-particle
transition operators. For a given Efimov trimer the universal properties of the
lowest associated tetramer are determined. The impact of this tetramer on the
atom-trimer and dimer-dimer collisions is analyzed. The reliability of the
three-body dimer-atom-atom model is studied.
