DOUBLE BETA DECAY AND BEYOND STANDARD MODEL PARTICLE PHYSICS

Neutrinoless nuclear double 0νββ decay, recently experimentally observed for ⁷⁶Ge on a confidence level of > 6 σ, has fundamental consequences for particle physics - violation of (total) lepton number, Majorana nature of the neutrino. It further leads to sharp restrictions for SUSY theories, sneutrino mass, right-handed W-boson mass, superheavy neutrino masses, compositeness, leptogenesis, violation of Lorentz violation and equivalence principle in the neutrino sector.

The masses of light neutrinos follow to be degenerate, and to be at least 0.22 ± 0.02 eV. This fixed the contribution of neutrinos as hot dark matter to ≥ 4.7% of the total observed dark matter. The neutrino mass determined might also solve the dark energy puzzle.

The observation of 0νββ decay is naturally a great challenge for future experiments, in particular also with other 0νββ - emitter isotopes. There are several important experiments under construction. Present experiments have hardly a chance to reach the sensitivity required for confirmation - although sometimes this impression is given (e.g. by unproperly comparing 1.5 σ limits (of CUORICINO etc.) with the 6σ result obtained for ⁷⁶Ge.