Type I seesaw mechanism for quasi degenerate neutrinos

Understand

We discuss symmetries and scenarios leading to quasi-degenerate neutrinos in type-I seesaw models.

• The existence of degeneracy in the present approach is not linked to any specific structure for the Dirac neutrino Yukawa coupling matrix $y_D$ and holds in general.
• Basic input is the application of the minimal flavour violation principle to the leptonic sector.
• Generalizing this principle, we assume that the structure of the right handed neutrino mass matrix is determined by $y_D$ and the charged lepton Yukawa coupling matrix $y_l$ in an effective theory invariant under specific groups ${\cal G}_F$ contained in the full symmetry group of the kinetic energy terms.