Neutrino masses, neutral vector bosons and the scale of B−L breaking

Extensions of the standard model with extra neutral vector bosons predict additional fermions whose allowed masses are constrained by the masses of the new vector bosons. For the minimal case with one extra Z′ boson and an extended gauge group contained in the unified group SO(10), we derive upper and lower bounds on the masses of heavy Majorana neutrinos. We also discuss implications for the standard model Higgs boson.