See-saw and supersymmetry

We review recent results on the connection between the see-saw mechanism and supersymmetry. It is shown that spontaneously broken B–L symmetry, in theories with a renormalizable see-saw, determines completely the low energy structure of the supersymmetric Standard Model: it implies exact R-parity. We then discuss how the violation of the survival principle in supersymmetric SO(10) naturally leads to an intermediate see-saw scale and the lowering of the unification scale. This affects the predictions for proton decay: p→π0e+ may be the dominant mode.