Fine tuning in an A4-based Tri-Bimaximal neutrino-mixing model

Understand

The A4 group stands in the basis of many models that predict Tri-Bimaximal neutrino mixing at leading order.

• We study the Altarelli-Feruglio A4 symmetry model and show that in order to produce as small value of r_{23} (ratio of mass-squared differences) as measured, it requires fine tuning.
• This observation is important for an evaluation of the model, since the problem it is trying to solve in the first place is the tuning of the three mixing angles.
• We get the required level of fine tuning for the model in both its basic form and its seesaw realization.