Double beta decay in left-right symmetric models
  Left-right symmetric models provide a natural framework for neutrinoless double beta ($\znbb$) decay. In the analysis of $\znbb$ decay in left-right symmetric models, however, it is usually assumed that all neutrinos are light. On the other hand, heavy {\it right-handed} neutrinos appear quite naturally in left-right symmetric models and should therefore not be neglected. Assuming the existence of at least one right-handed heavy neutrino, absence of $\znbb$ decay of $^{76}$Ge currently provides the following limits on the mass and mixing angle of right-handed W-bosons: $m_{W_R}\ge 1.1 $ TeV and $\tan(\zeta) \le 4.7 \times 10^{-3}$ for a particular value of the effective right-handed neutrino mass, $\emnv = 1$ TeV, and in the limit of infinitly massive doubly charged Higgs ($\Delta^{--}$). The effects of the inclusion of the Higgs triplet on $\znbb$ decay are also discussed. 
M. Hirsch, H.V. Klapdor-Kleingrothaus and O. Panella