Radiative neutrino masses in an SU(2) × U(1) model

Abstract

We extend the standard model with n L lepton doublets and n H Higgs doublets by adding n R right-handed neutrino singlets with a Yukawa term and a Majorana mass term. Assuming n L > n R there are n L − n R massless Majorana neutrinos at the tree level of which n L − n R − max(0, n L − n H n R) states acquire a mass by neutral Higgs exchange at the one-loop level. With heavy Majorana masses of the neutrino singlets this model combines the seesaw mechanism and radiative mass production to obtain naturally light neutrino masses. The minimal case n L = 3, n R = 1, n H = 2 is examined in detail including a phenomelogical discussion.