On the eta-eta' complex in the SD-BS approach
  The bound-state Schwinger-Dyson and Bethe-Salpeter (SD-BS) approach is chirally well-behaved and provides a reliable treatment of the eta-eta' complex although a ladder approximation is employed. Allowing for the effects of the SU(3) flavor symmetry breaking in the quark-antiquark annihilation, leads to the improved eta-eta' mass matrix. 
Dubravko Klabucar (Zagreb University), Dalibor Kekez (Institute Rudjer   Boskovic), Michael D. Scadron (University of Arizona)