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 $δ$. 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 $\sin δ\sim O(1)$. A more detailed examination of the model, although confirming their result, is seen to be also compatible with having a phase $δ_o= π/3$ imprinted on the Hermitian Yukawa matrices, leading to $\sin δ\simeq \sin δ_o$.

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