Matrix elements of unstable states
  Using the language of non-relativistic effective Lagrangians, we formulate a systematic framework for the calculation of resonance matrix elements in lattice QCD. The generalization of the L\"uscher-Lellouch formula for these matrix elements is derived. We further discuss in detail the procedure of the analytic continuation of the resonance matrix elements into the complex energy plane and investigate the infinite-volume limit. 
V. Bernard, D. Hoja, U.-G. Mei{\ss}ner, A. Rusetsky
hep-lat hep-ph nucl-th