In this seminar, I will discuss recent efforts to assess the complementarity of direct searches at fixed target experiments and searches for neutrinoless double beta (0νββ) decay in probing the Majorana vs. pseudo-Dirac nature of a Heavy Neutral Lepton (HNL) pair. Firstly, I will outline a phenomenological parametrisation relating the active-sterile mixing strengths to the neutrino oscillation data, assuming that the HNL pair generates masses for two light neutrinos. I will then summarise the possible constructive or destructive interference of the HNL pair with the light neutrino contribution in 0νββ decay and the production and decay of HNLs in fixed target experiments, which depend on the active-sterile mixing strengths and CP phases in the HNL sector. Finally, I will show what signals at LEGEND-1000 and DUNE (or a signal at one or neither of the experiments) imply about the HNL parameter space; in particular, the mass splitting between the HNL pair.
https://indico.ijs.si/event/1561/