Nuclear Structure Aspects of Neutrinoless Double Beta Decay
  We decompose the neutrinoless double-beta decay matrix elements into sums of products over the intermediate nucleus with two less nucleons. We find that the sum is dominated by the J^pi=0^+ ground state of this intermediate nucleus for both the light and heavy neutrino decay processes. This provides a new theoretical tool for comparing and improving nuclear structure models. It also provides the connection to two-nucleon transfer experiments. 
B. A. Brown, M. Horoi and R. A. Sen'kov
nucl-th