Neutrinoless Quadruple Beta Decay

TL;DR

This paper explores a novel form of lepton number violation allowing neutrinoless quadruple beta decay in certain isotopes, proposing a model where this process is possible despite neutrinos being Dirac particles.

Contribution

The paper introduces a simple model demonstrating lepton number violation by four units, enabling neutrinoless quadruple beta decay even with Dirac neutrinos, and identifies promising isotopes for experimental detection.

Findings

Neutrinoless quadruple beta decay is theoretically possible in specific isotopes.

Nd-150 is identified as the most promising candidate for observing this decay.

Expected lifetimes for the decay are extremely long, making experimental detection challenging.

Abstract

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. Analogous processes, such as neutrinoless quadruple electron capture, are also possible. The expected lifetimes are extremely long, and experimental searches are challenging.