CP Violation in Hierarchical Yukawa Models
  Because 4-dimensional CP is a good symmetry of many higher-dimensional theories, this suggests the possible existence of a universal CP-violating phase originating from the process of compactification. Such a phase, if it existed, would not be easy to uncover since the phases in Yukawa matrices are not simply related to the observed CKM phase $\delta$. Hierarchical Yukawa models of the type arising in F-theory GUT models provide an interesting exception. Recently, Heckman and Vafa studied a particular F-theory GUT model with hierarchical Yukawa matrices with complex phases of O(1) and showed, by examining the Jarlskog invariant, that this model leads to $\sin \delta \sim O(1)$. A more detailed examination of the model, although confirming their result, is seen to be also compatible with having a phase $\delta_o= \pi/3$ imprinted on the Hermitian Yukawa matrices, leading to $\sin \delta \simeq \sin \delta_o$. 
R. D. Peccei
hep-ph hep-th