An unorthodox alternative for righthanded neutrinos: Lefthanded see-saw

A new lefthanded see-saw mechanism is constructed, implying both the smalln ess of active-neutrino masses and decoupling of heavy passive neutrinos, si milarly to the situation in the case of conventional see-saw. But now, in p lace of the conventional righthanded neutrinos, the lefthanded sterile neut rinos play the role of heavy passive neutrinos, the righthanded neutrinos a nd righthanded sterile neutrinos being absent. Here, the lefthanded sterile neutrinos are different from charge conjugates of conventional righthanded neutrinos because their lepton numbers differ. In this case, the neutrino mass term is necessarily of pure Majorana type.