Nuclear Double Beta Decay, Fundamental Particle Physics, Hot Dark Matter, And Dark Energy

摘要

Nuclear double beta decay, an extremely rare radioactive decay process, is -in one of its variants - one of the most exciting means of research intoparticle physics beyond the standard model. The large progress in sensitivityof experiments searching for neutrinoless double beta decay in the last twodecades - based largely on the use of large amounts of enriched source materialin "active source experiments" - has lead to the observation of the occurrenceof this process in nature (on a 6.4 sigma level), with the largest half-lifeever observed for a nuclear decay process (2.2 x 10^{25} y). This hasfundamental consequences for particle physics - violation of lepton number,Majorana nature of the neutrino. These results are independent of anyinformation on nuclear matrix elements (NME)*. It further leads to sharprestrictions for SUSY theories, sneutrino mass, right-handed W-boson mass,superheavy neutrino masses, compositeness, leptoquarks, violation of Lorentzinvariance and equivalence principle in the neutrino sector. The masses oflight-neutrinos are found to be degenerate, and to be at least 0.22 +- 0.02 eV.This fixes the contribution of neutrinos as hot dark matter to >=4.7% of thetotal observed dark matter. The neutrino mass determined might solve also thedark energy puzzle. *(It is briefly discussed how important NME for 0nubb decayreally are.)