The Seesaw Mechanism in Quark-Lepton Complementarity

Understand

We systematically construct realistic mass matrices for the type-I seesaw mechanism out of more than 20 trillion possibilities.

• We use only very generic assumptions from extended quark-lepton complementarity, i.e., the leptonic mixing angles between flavor and mass eigenstates are either maximal, or parameterized by a single small quantity epsilon that is of the order of the Cabibbo angle epsilon theta_C.
• The small quantity epsilon also describes all fermion mass hierarchies.
• We show that special cases often considered in the literature, such as having a symmetric Dirac mass matrix or small mixing among charged leptons, constitute only a tiny fraction of our possibilities.