The Neutrinoless Double Beta Decay, Physics beyond the Standard Model and the Neutrino Mass

TL;DR

This paper reviews methods to calculate neutrinoless double beta decay rates, explores how to identify the dominant decay mechanism experimentally, and estimates the effective Majorana neutrino mass from potential measurements.

Contribution

It compares different nuclear matrix element calculation methods and investigates experimental strategies to determine the leading decay mechanism.

Findings

Calculated matrix elements using QRPA, Shell Model, PHFB, and IBA.

Analyzed mechanisms including light and heavy Majorana neutrino exchange, SUSY contributions.

Estimated effective Majorana neutrino mass as 0.24 eV from potential decay measurements.

Abstract

The Neutrinoless double beta Decay allows to determine the effectice Majorana electron neutrino mass. For this the following conditions have to be satisfied: (i) The neutrino must be a Majorana particle, i. e. identical to the antiparticle. (ii) The half life has to be measured. (iii)The transition matrix element must be reliably calculated. (iv) The leading mechanism must be the light Majorana neutrino exchange. The present contribution studies the accuracy with which one can calculate by different methods: (1) Quasi-Particle Random Phase Approach (QRPA), (2) the Shell Model (SM), (3) the (before the variation) angular momentum projected Hartree-Fock-Bogoliubov method (PHFB)and the (4) Interacting Boson Approach (IBA). In the second part we investigate how to determine experimentally the leading mechanism for the Neutrinoless Double Beta Decay. Is it (a) the light Majorana neutrino exchange as one assumes to determine the effective Majorana neutrino mass, ist it the heavy left (b) or right handed (c) Majorana neutrino exchange allowed by left-right symmetric Grand Unified Theories (GUT's). Is it a mechanism due to Supersymmetry e.g. with gluino exchange and R-parity and lepton number violating terms. At the end we assume, that Klapdor et al. have indeed measured the Neutrinoless Double Beta Decay(, although contested,)and that the light Majorana neutrino exchange is the leading mechanism. With our matrix elements we obtain then an effective Majorana neutrino mass of: <m(nu)> = 0.24 [eV], exp (pm) 0.02; theor. (pm) 0.01 [eV]