Phenomenological Schwinger-Dyson approach to eta-eta' mass matrix
  It is reviewed pedagogically how a very successful description of the eta-eta' mass matrix can be achieved in the consistently coupled Schwinger-Dyson and Bethe-Salpeter approach in spite of the limitations of the ladder approximation. This description is in agreement with both phenomenology and lattice results. 
Dalibor Kekez (Institute Rudjer Boskovic) and Dubravko Klabucar   (Zagreb University)