Light neutrino and heavy particle exchange in $\nbb$-decay
  A simple and precise method is presented to compare contributions to neutrinoless double-beta decay ($\nbb$-decay) from heavy particle exchange and light Majorana neutrino exchange. This procedure makes no assumptions about the momentum transfer between the two nucleons involved in the $\nbb$-decay process. It is shown that for a general particle physics model, the characteristic $\nbb$-decay scale $> 4.4$ TeV when all the coupling constants are assumed to be natural and of ${\cal{O}}(1)$. 
Gary Pr\'ezeau