From type | to type || see-saw models and leptogenesis

by S.F. King (Department of Physics and Astronomy, University of Southampton)

Friday 23 Jul 2004, 14:00 → 15:00 Europe/Zurich

TH Auditorium (CERN)

It is well known that natural models of hierarchical neutrino masses and bi-large neutrino mixing can originate from the type I see-saw mechanism, using sequential dominance of right-handed neutrinos. However within this framework it is rather difficult to arrange for a partially degenerate neutrino. In this talk I show how such type I see-saw models can be naturally up-graded to type II see-saw models, allowing partially degenerate neutrino masses with a possible signal observable in the next generation of neutrinoless double beta decay experiments. I also show that in such type II models the leptogenesis asymmetry parameter becomes proportional to the neutrino mass scale, in sharp contrast to the type I case, which leads to an upper bound on the neutrino mass scale, allowing lighter right-handed neutrinos and hence making leptogenesis more consistent with the gravitino constraints in supersymmetric models.