Non-Standard Mechanisms for Neutrinoless Double Beta Decay

Neutrinoless double beta decay is a powerful tool to probe not only for Majorana neutrino masses but for lepton number violating physics in general. We discuss relations between lepton number violation, double beta decay and neutrino mass, provide an overview of the general Lorentz invariant parametrization of the double beta decay rate and highlight a number of different new physics models showing how different mechanisms can trigger double beta decay.