Neutrinoless Quadruple Beta Decay

Understand

We point out that lepton number violation is possible even if neutrinos are Dirac particles.

• We illustrate this by constructing a simple model that allows for lepton number violation by four units only.
• As a consequence, neutrinoless double beta decay is forbidden, but neutrinoless quadruple beta decay is possible: $(A,Z) \to (A,Z+4) + 4 e^-$.
• We identify three candidate isotopes for this decay, the most promising one being Nd-150 due to its high $Q_{0\nu 4\beta}$-value of 2 MeV.