Universality of Strength of Yukawa Couplings, Quark Singlets and   Strength of CP Violation
  We analyse the strength of CP violation in an extension of the standard model with an extra $Q=-1/3$ vector-like singlet quark, in the framework of the hypothesis of universality of strength of Yukawa couplings connecting standard quarks. We show that the correct pattern of quark masses and mixing can be obtained, including the observed strength of CP violation. 
G.C. Branco, H.R. Cola\c{c}o Ferreira, A.G. Hessler and J.I.   Silva-Marcos
hep-ph