Neutrinoless double beta decay and neutrino mass

Abstract

The observation of neutrinoless double beta decay will have important consequences. First it will signal that lepton number is not conserved and the neutrinos are Majorana particles. Second, it represents our best hope for determining the absolute neutrino mass scale at the level of a few tens of meV. To achieve the last goal, however, certain hurdles have to be overcome involving particle, nuclear and experimental physics. Particle physics is important since it provides the mechanisms for neutrinoless double beta decay. In this review we emphasize the light neutrino mass mechanism. Nuclear physics is important for extracting the useful information from the data. One must accurately evaluate the relevant nuclear matrix elements, a formidable task. To this end, we review the recently developed sophisticated nuclear structure approaches, employing different methods and techniques of calculation. We also examine the question of quenching of the axial vector coupling constant, which may have important consequences on the size of the nuclear matrix elements. From an experimental point of view it is challenging, since the life times are extremely long and one has to fight against formidable backgrounds. One needs large isotopically enriched sources and detectors with good energy resolution and very low background.

The unfinished fabric of the three neutrino paradigm

“…In the absence of novel estimates of NME covariances, we shall use the only available results of [82] at face value. We have checked that, in any case, the NME uncertainties estimated therein are conservative enough to cover within ±2σ most (and within ±3σ all) of the M i values compiled in [60,[75][76][77][78][79][80][81] for the three nuclides.…”

“…The |M i | embed complex nuclear physics, currently treated in a variety of approaches that, unfortunately, still carry significant uncertainties despite the theoretical progress, see e.g. the recent reviews in [60,[75][76][77][78][79][80][81]. It is common practice to select a set of published values {M i } in order to obtain a set of upper bounds {m ββ }, whose spread may be taken as indicative of the theoretical uncertainties; see [61] for a very recent application.…”

Global constraints on absolute neutrino masses and their ordering

“…where m ββ is given in Eq. ( 5), G is the (calculable) phase space and M is the nuclear matrix element (NME) for a candidate nucleus [15,[50][51][52].…”

Zooming in on eV-MeV Scale Sterile Neutrinos in light of Neutrinoless Double Beta Decay

“…This is another extension of SM, where the model contains light and heavy sterile neutrinos 4 , which can give large contribution in 0νββ process. Several studies [42,43,51,53,[69][70][71][72][73][74][75][76][77][78][79][80][81][82][83] have focused on sterile neutrinos with mass > 100 MeV, and large contribution in the LNV process. Here, instead we consider some of the sterile neutrino states in the < 100 MeV mass range.…”

“…The 0νββ process is the transition (A, Z) → (A, Z + 2) + 2e − with no neutrino being emitted [39][40][41]. The process is lepton number violating [42,43]. Depending on the mixing of the right-handed neutrinos with active neutrinos in type-I/Extended Seesaw, or the interaction of these right-handed neutrinos with the right-handed gauge boson in left-right symmetric extension, these right-handed neutrino states may give significant contributions in 0νββ process compared to the three SM neutrino contributions, and thus opening up the scope of detection of these Majorana neutrinos via 0νββ process.…”