Heavy Neutral Leptons Beyond Simplified Scenarios

Heavy neutral leptons (HNL) constitute the building blocks of several neutrino mass generation mechanisms. Experimental searches depend on their masses and mixings with the active neutrinos, and exclusion regions in the plane of mass and mixing rely most of the time on two assumptions: $(i)$ the existence of $one$ HNL, which $(ii)$ mixes dominantly with only $one$ lepton flavor. In this work we discuss how to reinterpret the limits from collider searches relaxing these assumptions, providing a simple recipe to recast the bounds in models with generic mixing patterns, and in which at least two HNLs are coupled to the active sector.