A minimal see-saw model for hierarchical neutrino masses with large mixing

The atmospheric and solar neutrino oscillation data suggest hierarchical ne utrino masses with at least one large mixing. The simplest see-saw models f or reconciling the two features are U(1) extensions of the SM with flavour dependent gauge charges. I discuss a minimal model of this type containing two heavy right-handed neutrinos, which have normal Dirac couplings to nu(m u) and nu(tau) but suppressed ones to nu(e). It can naturally account for t he large (small) mixing solutions to the atmospheric (solar) neutrino oscil lation data.