Scaling in the Neutrino Mass Matrix, mu-tau Symmetry and the See-Saw Mechanism

Understand

The scaling hypothesis postulates proportionality of two columns of the Majorana neutrino mass matrix in the flavor basis.

• This Ansatz was shown to lead to an inverted hierarchy and U_{e3} = 0.
• We discuss theoretical and phenomenological properties of this hypothesis.
• We show that (i) the neutrino mass matrix with scaling follows as a consequence of a generalized mu-tau symmetry imposed on the type-I see-saw model; (ii) there exists a unique texture for the Dirac mass matrix m_D which leads to scaling for arbitrary Majorana matrix M_R in the context of the type-I see-saw mechanism; (iii) unlike in the mu-tau symmetric case, a simple model with two right-handed neutrinos and scaling can lead to successful leptogenesis both with and without the inclusion of flavor effects.