Neutrinoless Double Beta Decay Potential in a Large Mixing Angle World

Abstract

Abstract. We discuss the possibility of reconstructing the neutrino mass spectrum from the complementary processes of neutrino oscillations and double beta decay in view of the new data of Super-Kamiokande presented at the Neutrino2000 conference. Since the large mixing angle solution is favored, now, the prospects to observe double beta decay and provide informations on the absolute mass scale in the neutrino sector have been improved. Double Beta decay and neutrino oscillationsNeutrinos finally have been proven to be massive by atmospheric and solar neutrino oscillation experiments. However, the absolute scale of neutrino masses, a necessary ingredient for reconstructing beyond the standard model physics, is still unknown, since informations obtained in neutrino oscillation experiments regard the mass squared differences and mixing angles, only. Only both neutrino oscillations and neutrinoless double beta decay together could solve this absolute neutrino mass problem [1,2,3]. In this paper we discuss the most recent data , as presented by the Super-Kamiokande Collaboration at the Neutrino2000 conference [4]. The small mixing angle solution for solar neutrinos is ruled out, now, at 90 % C.L. Moreover, solutions including sterile neutrinos seemed to be disfavored both for atmospheric as well as for solar neutrinos. In the following we thus will restrict ourselves to a three neutrino framework, omitting the LSND anomaly. (For a discussion of the small mixing angle solution and four neutrino scenarios see [1]). A global analysis in a three neutrino framework yield the following favored regions [5,6]:• Solar neutrino oscillations favor ν e − ν e oscillations within the large mixing angle (LMA) MSW solution: ∆m 2 ⊙ = 3 (1 − 10) · 10 −5 eV 2 tan 2 θ ⊙ = 0.5 (0.2 − 0.6), where the bestfit is given with the 90 % C.L. region in the brackets. Also a small region in the QVO(quasi-vacuum-oscillation)-LOW regime at

Implications of Observed Neutrinoless Double Beta Decay

“…We allow possible variation of the phases in the masses to check for cancellation. This gives a range for m ee , which is similar to the values obtained in an earlier analysis [28]. There are some changes, which come due to the new input from SNO.…”

“…Thus the present observation of the 0νββ decay would rule out a class of models where this cancellation takes place partially or fully. Moreover constraints from the atmospheric and solar neutrinos and Lab limits could be used in conjunction with the present limit on 0νββ decay to discriminate some of the possible mass spectra following the analysis of [28] and with one new consideration that in some cases electroweak radiative corrections destabilize the LOW, VO and Just So solutions of the solar neutrinos.…”

Status of Evidence for Neutrinoless Double Beta Decay, and the Future: Genius and Genius-Tf

“…[50,51]), the absolute scale of the neutrino mass is still unknown. Information from double beta decay experiments is indispensable to solve these questions [5,6]. Another important problem is that of the fundamental character of the neutrino, whether it is a Dirac or a Majorana particle [7,8].…”

Majorana neutrinos with split fermions in extra dimensions

“…Here we do not require any bulk particles and the neutrinos get a lepton number violating Majorana mass. Moreover, in this scenario the neutrino masses could be almost degenerate, so that they can contribute to the dark matter of the universe and also explain the neutrinoless double beta decay [10,11]. In other models of neutrino masses in extra dimensions there is no natural mechanism to explain the almost degenerate neutrinos.…”

“…In this case an almost degenerate neutrino comes out naturally. It would then be possible to explain the recent observation of the neutrinoless double beta decay [11] by this hybrid model. In this case the neutrino mass matrix becomes,…”