We propose a realistic model with Majorana neutrinos in the framework of unifying the three generations of fermions by point interactions in an extra dimension. This model can simultaneously explain the origin of fermion generations, fermion masses and mixing, and the smallness of the masses of Majorana neutrinos. We show that there are two mechanisms working together to suppress the neutrino masses significantly, so we do not have to introduce a very large extra-dimension cutoff scale. One is the type-I seesaw mechanism and the other is the overlap integration of localized lepton wave functions. A singlet scalar with an exponential-like vacuum expectation value plays a central role in these two mechanisms. For consistency in this model we introduce a $U(1{)}^{\prime }$ gauge symmetry, which will be broken by the singlet scalar. Parameters of our model can fit the masses and flavor mixing data well. These parameters can also predict all $CP$ violating phases including the Majorana ones and accidentally rescue the proton from decay.

• Received 29 October 2015

DOI:https://doi.org/10.1103/PhysRevD.93.036003