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Free keywords:
High Energy Physics - Phenomenology, hep-ph,High Energy Physics - Experiment, hep-ex,Nuclear Experiment, nucl-ex,Nuclear Theory, nucl-th
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.