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Abstract

Neutrinoless double beta decay (0νββ) is the most promising experimental probe of lepton number violating (LNV) physics beyond the Standard Model. Its discovery may provide profound insights into the mechanism of neutrino mass generation as well as the observed baryon asymmetry of the universe. While the most simple interpretation of a 0νββ signal is in terms of a LNV Majorana neutrino mass term, other LNV mechanisms may provide the leading contribution to the 0νββ transition amplitude. Effective field theories (EFTs) are an efficient tool to describe and study the various LNV mechanisms of 0νββ in a model-independent way. In this work, we study the implications of a future 0νββ discovery by showcasing how different LNV mechanisms of 0νββ can be disentangled via measurements of the half-life and electron kinematics in various isotopes. By providing a proof-of-concept model that generates a non- trivial 0νββ half-life in a model with a lepton number conserving vacuum ground-state Lagrangian, we challenge the long-standing black-box theorem, which relates a 0νββ observation to the Majorana nature of neutrinos. This is achieved via the capture of a lepton number carrying scalar field from a dark background. Finally, we automated the applied EFT framework in the Python tool νDoBe and showcase example use-cases.