Transition Operators Entering Neutrinoles Double Electron Capture to   Excited Nuclear States
  We construct the effective transition operators relevant for neutrinoless double electron capture leading to final nuclear states different than $0^{+}$. From the structure of these operators we see that, if such a process is observed experimentally, it will be very helpful in singling out the very important light neutrino mass contribution from the other lepton violating mechanisms 
J.D. Vergados (Theoretical Physics Division, University of Ioannina,   Ioannina, Greece)
hep-ph