Hosted by: Xin Qian

Search for the neutrinoless double beta decay is one of the main goals of nuclear physics community worldwide. If observed, it would be an example of "physics beyond the Standard Model", showing that the lepton number is not a conserved quantity and that neutrinos are massive Majorana fermions. After introducing the subject and its particle physics consequences I will concentrate on the issue of evaluation of the nuclear matrix elements. Despite decades of effort and hundreds of publications, different approaches give results that differ by roughly a factor of three, and it is difficult to decide which of them is the most realistic. I will describe the strengths and weaknesses of the nuclear models used. In addition, I will discuss the problem of "quenching", i.e. of reduction of the matrix elements of weak axial current in complex nuclei, that potentially affects the neutrinoless double beta decay matrix element values signiffcantly