$S_3$ model for lepton mass matrices with nearly minimal texture

We propose a simple extension of the electroweak standard model based on the discrete $S_3$ symmetry that is capable of realizing a nearly minimal Fritzsch-type texture for the Dirac mass matrices of both charged leptons and neutrinos. This is achieved with the aid of additional $Z_5$ and $Z_3$ symmetries, one of which can be embedded in $U(1{)}_{B-L}$. Five complex scalar singlet fields are introduced in addition to the standard model with right-handed neutrinos. Although more general, the modified texture of the model retains the successful features of the minimal texture without fine-tuning; namely, it accommodates the masses and mixing of the leptonic sector and relates the emergence of large leptonic mixing angles with the seesaw mechanism. For large deviations of the minimal texture, both quasidegenerate spectrum or inverted hierarchy are allowed for neutrino masses.

Figure 1

${sin}^2{\theta }_{13}$ as a function of ${sin}^2{\theta }_{23}$; the symbols $\times$ correspond to ${\beta }_{0l}={\beta }_{\nu }=0$ while dots correspond to $({\beta }_{0l},{\beta }_{\nu })=(1,-0.418)$.

Figure 2

${sin}^2{\theta }_{12}$ as a function of the lightest neutrino mass; the symbols $\times$ correspond to ${\beta }_{0l}={\beta }_{\nu }=0$ while dots correspond to $({\beta }_{0l},{\beta }_{\nu })=(1,-0.418)$.