Neutrino masses

Abstract

The various experiments on neutrino oscillation evidence that neutrinos have indeed non-zero masses but cannot provide the absolute neutrino mass scale. This scale of neutrino masses is very important for understanding the evolution and the structure formation of the universe as well as for nuclear and particle physics beyond the present Standard Model. Complementary to deducing constraints on the sum of all neutrino masses from cosmological observations, two different methods to determine the neutrino mass scale in the laboratory are pursued: the search for neutrinoless double β-decay and the direct neutrino mass search by investigating single β-decays or electron captures. The former method is not only sensitive to neutrino masses but also probes the Majorana character of neutrinos and thus lepton number violation with high sensitivity. Currently quite a few experiments using different techniques are being constructed, commissioned, or are even running, which aim for a sensitivity on the neutrino mass of O(100) meV. The principal methods and these experiments are discussed in this short review. © 2013 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.