Probing right-handed neutrinos dipole operators

We consider the minimal see-saw extension of the Standard Model with two right-handed singlet fermions N-1,N-2 with mass at the GeV scale, augmented by an effective dipole operator between the sterile states. We firstly review current bounds on this effective interaction from fixed-target and collider experiments, as well as from astrophysical and cosmological observations. We then highlight the prospects for testing the decay N-2 -> N-1 gamma induced by the dipole at future facilities targeting long-lived particles such as ANUBIS, CODEX-b, FACET, FASER 2, MAPP and SHiP.