Lepton number violation (LNV) is a central component in theories of leptogenesis and Majorana neutrino masses, yet it has never been observed experimentally. In this talk I will review the most promising observables of LNV from an effective field theory (EFT) perspective, including meson decays and colliders. I will then show why EFT is not well-suited to describe constraints coming from small neutrino masses, and instead derive new constraints using simplified models. The results of this latter analysis can be used as a phenomenological tool to connect many different New Physics models to neutrino masses, which I will demonstrate using the recently reported excess in rare B-meson decays at Belle II.
Ankita Budhraja, Juraj Klaric, Johannes Michel