Correlated Hierarchy, Dirac Masses and Large Mixing Angles

Abstract

We introduce a new parametrization of the MNS lepton mixing matrix which separates the hierarchical Grand Unified relations among quarks and leptons. We argue that one large angle stems from the charged leptons, the other from the seesaw structure of the neutral lepton mass matrix. We show how two large mixing angles can arise naturally provided there are special requirements on the Dirac ($ΔI_{\rm w}=1/2$) and Majorana ($ΔI_{\rm w}=0$) masses. One possibility is a correlated hierarchy between them, the other is that the $ΔI_{\rm w}=0$ Majorana mass has a specific texture; it is Dirac-like for two of the three families.