Tri-bimaximal lepton mixing from symmetry only

Understand

We construct a model for tri-bimaximal lepton mixing which employs only family symmetries and their soft breaking; neither vacuum alignment nor supersymmetry, extra dimensions, or non-renormalizable terms are used in our model.

• It is an extension of the Standard Model making use of the seesaw mechanism with five right-handed neutrino singlets.
• The scalar sector comprises four Higgs doublets and one complex gauge singlet.
• The horizontal symmetry of our model is based on the permutation group S_3 of the lepton families together with the three family lepton numbers--united this constitutes a symmetry group Delta(6\infty^2).