Mass hierarchy and flavour mixing from discrete symmetries

are fully compatible with the so-called Tri-Bimaximal (TB) mixing pattern which corresponds to a maximal θ23, an zero θ13 and a “magic” value of solar angle: sin 2 θ12 = 1/3. It is well known that the lepton mixing angles can be understood by a mechanism of vacuum misalignment in flavour space occurring in theories with non-abelian flavour symmetries [2]. Also the charged lepton mass hierarchy can be achieved via spontaneous breaking of the flavour symmetry. However, in most cases, a separate component of the flavour group is exploited to this purpose. Quite frequently the flavour group is of the type D × U(1)FN where D is a discrete component that controls the mixing angles and U(1)FN [3] is an abelian continuous symmetry that describes the mass hierarchy. In the present talk, we will consider a class of flavour symmetries in which the same flavon fields producing the mixing pattern are also responsible for the mass hierarchy employing an hybrid breaking pattern [4]. The idea is to selectively couple charged leptons and neutrinos to two different sets of flavons, Φe and Φν , respectively. The VEV of Φν breaks G down to a residual symmetry in the neutrino sector preferably containing the νμ − ντ exchange symmetry as indicated by the oscillation data. While, the VEV of Φe would break G down to a different subgroup, maximally breaking the previous νμ−ντ symmetry, guaranteeing a hierarchical and quasi diagonal matrix ml.