$\Delta L \ge 4$ processes

Understand

We discuss the experimental prospects for observing processes which violate lepton number ($\Delta L$) in four units (or more).

• First, we reconsider neutrinoless quadruple beta decay, deriving a model independent and very conservative lower limit on its half-life of the order of $10^{41}$ ys for $^{150}$Nd.
• This renders quadruple beta decay unobservable for any feasible experiment.
• We then turn to a more general discussion of different possible low-energy processes with values of $\Delta L \ge 4$.