Phases in Leptonic Mass Matrices: Higher Order Invariants and   Applications to Models
  We discuss complex rephasing invariants of charged lepton and neutrino mass matrices and associated theorems which determine in general (i) the number of physically meaningful phases in these matrices and (ii) which elements of these matrices can be rendered real by rephasings. New results are presented on higher order complex invariants and the application of the methods to several models. 
A. Kusenko and R. Shrock