CP Phases in Models with Some Fermion Masses Vanishing and/or Degenerate
  We count the number of CP breaking phases in models with $SU(2)_L\times U(1)_Y$ and $SU(2)_L\times SU(2)_R\times U(1)_{B-L}$ electroweak gauge groups and extended matter contents with some fermion masses vanishing and/or degenerate. Quarks and leptons, including Majorana neutrinos, are treated in a similar way. CP violation is characterized in the mass-eigenstate and in the weak-eigenstate bases. Necessary and sufficient conditions for CP conservation, invariant under weak basis redefinitions are also studied in these models. CP violating factors entering in physical observables and only invariant under phase redefinitions are discussed. 
F. del Aguila, M. Zralek