Hosted by: Peter Petreczky

The question of whether or not neutrinos are Majorana particles and, if so, what is their average mass remains one of the most fundamental problems in physics today. The average neutrino mass can be obtained from neutrinoless double beta decay. The inverse half-life for this process is given by the product of a phase space factor (PSF), a nuclear matrix element (NME) and whatever physics there is beyond the standard model. In this talk, the theory of double beta decay, both with and without the emission of neutrinos, will be reviewed, and recent calculations of the PSF and NME will be presented. From these and from experimental limits on the half-life of neutrinoless double beta decay, one can extract limits on the neutrino mass, both for the exchange of light (mνá1keV) and heavy (mνà1GeV) neutrinos. Current limits will be discussed. Finally, the question of how many neutrino species there are will be briefly addressed, including the possibility of sterile neutrinos with masses in the intermediate range keV-GeV.