Neutrinoless Double-Beta Decay and Neutrino Mass Spectrum

Abstract

Implications of the neutrinoless double-beta (ββ_0ν) decay searches for the neutrino mass and mixing spectrum are discussed. We consider properties of the effective Majorana mass, m _ee, relevant for ββ_0ν decay. We find predictions or limits for m _ee in the three neutrino schemes which explain the atmospheric and solar neutrino data. We show how combined analysis of results from ββ_0ν-decay searches, oscillation experiments as well as direct measurements of neutrino mass will allow to identify the spectrum. In this connection, several test equalities which relate m _ee and the oscillation parameters in the context of certain neutrino spectra are suggested. Two issues are important for realization of the identification program: (i) high enough accuracy of determination of m _ee which requires reliable knowledge of the nuclear matrix elements, and (ii) possibility to identify the mechanism of the ββ_0ν decay, in particular, to disentangle the decay due to exchange of the light Majorana neutrino and mechanisms related to exchange of heavy particles with m≫1/r _nuclei.