Understanding the differences in neutrino and charged-fermion flavour structures

Abstract

We present a new mechanism to explain naturally and through a common flavour symmetry the mildly hierarchical neutrino masses with large mixings and the hierarchical Yukawa matrices with small mixing angles. Although this mechanism is not linked to a particular flavour symmertry, it is particularly simple in the framework of a SU(3) flavour symmetry. In this model, we obtain exactly maximal atmospheric mixing, large although not maximal solar mixing and a normal neutrino hierarchy. All neutrino parameters are basically fixed. For instance, we predict that the angle $\theta_{13}$ comes entirely from the charged lepton sector and, using the difference of the solar angle from maximality, we can fix the mass of lightest neutrino.