Abstract :
We consider properties of the CKM phase in the heterotic orbifold models. We find that at the renormalizable level the CKM phase vanishes identically for the prime orbifolds, whereas it can be nonzero for some nonprime orbifolds. In particular, we study in detail the Z6-I orbifold which allows for a nontrivial CKM phase and analyze the modular properties of the corresponding Jarlskog invariant. The CKM phase is shown to vanish if the moduli fields are stabilized at ImTi=±1/2.
