Investigating two heavy neutral leptons neutrino seesaw mechanism at SHiP

One of the main purposes of the SHiP experiment is to shed light on neutrino mass generation mechanisms like the so-called seesaw one. We consider a minimal type-I seesaw neutrino mass mechanism model with two heavy neutral leptons (right-handed or sterile neutrinos) with arbitrary masses. The extremely high active-sterile mixing angle requires a correlation between the phases of the Dirac neutrino couplings. Actual experimental limits on the half-life of neutrinoless double beta decay 0$\nu$$\beta$$\beta$-rate on the active-sterile mixing angle are not significative for SHiP.