Neutrino-less Double Beta Decay and Particle Physics
Werner Rodejohann
TL;DR
The paper surveys the particle physics aspects of $0νββ$, a lepton-number-violating process whose observation would confirm LNV and the Majorana nature of neutrinos. It contrasts the standard light Majorana neutrino exchange mechanism with various non-standard realizations (e.g., heavy neutrino exchange, left-right symmetry, Majorons, SUSY scenarios) and discusses the Schechter-Valle black-box theorem linking any mechanism to a Majorana mass. The analysis shows how decay rates decompose into a phase-space factor $G_x(Q,Z)$, a nuclear-matrix element $M_x(A,Z)$, and a particle-physics factor $η_x$, and outlines experimental challenges and strategies for distinguishing among mechanisms. It compiles current experimental limits on $T_{1/2}^{0ν}$ and the corresponding bounds on $⟨m_{ee}⟩$ across isotopes, and discusses future prospects for tightening constraints and identifying the underlying mechanism.
Abstract
We review the particle physics aspects of neutrino-less double beta decay. This process can be mediated by light massive Majorana neutrinos (standard interpretation) or by something else (non-standard interpretations). The physics potential of both interpretations is summarized and the consequences of future measurements or improved limits on the half-life of neutrino-less double beta decay are discussed. We try to cover all proposed alternative realizations of the decay, including light sterile neutrinos, supersymmetric or left-right symmetric theories, Majorons, and other exotic possibilities. Ways to distinguish the mechanisms from one another are discussed. Experimental and nuclear physics aspects are also briefly touched, alternative processes to double beta decay are discussed, and an extensive list of references is provided.