Double beta decay, supersymmetry and lepton number violation

Neutrinoless double beta (0νββ) decay violates lepton number and is therefore a sensitive probe of physics beyond the standard model. Limits from 0νββ decay are usually expressed in terms of limits on the Majorana neutrino mass, the best experiment now giving left angle mν right angle ≤0.5 eV. However, in supersymmetric extensions of the SM there can be other sources of lepton number violation than the neutrino mass, the best-known example being Rp-violation. 0νββ decay provides the most stringent limits on certain Rp MSSM parameters, ruling out first generation squarks as a possible explanation of the recent HERA high Q2-events. Furthermore, current low-energy constraints on and future collider phenomenology of (B-L) violating sneutrino masses are discussed. As has been proven recently such a (B-L) violating sneutrino mass is a necessary ingredient of any supersymmetric model with finite Majorana neutrino masses. (orig.)