Baryogenesis and the scale of B-L breaking

In unified theories with right-handed neutrinos the scale of B − L breaking can a priori vary between the unification scale and the Fermi scale of electroweak symmetry breaking. We derive upper and lower bounds on the masses of light and heavy Majorana neutrinos and on the scale of B − L breaking from the requirement that the cosmological baryon asymmetry is generated before the electroweak phase transition. Baryogenesis poses a serious problem for extended gauge theories with heavy neutrinos and neutral vector bosons in the TeV mass range