Natural Kobayashi-Maskawa Model of CP Violation and Flavor Physics
  We explore the possible tie between the naturalness of having a very small strong CP $\theta$ parameter in the Kobayashi-Maskawa Model and the flavor symmetry. We provide many examples in which the flavor symmetry group at high energy can naturally give rise to Kobayashi-Maskawa Model at low energy with a naturally small theta. 
Darwin Chang and Wai-Yee Keung