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Suppressing Proton Decay by Cancellation in S_4 Flavor Symmetric Extra U(1) Model

We consider proton stability based on E_6 inspired extra U(1) model with S_4 flavor symmetry. In this model, a long life time of proton is realized by the flavor symmetry. One of the interesting effects of flavor symmetry is that the proton decay widths of p -> mu^+, X are suppressed by cancellation. This suppression mechanism is important in the case that Yukawa coupling constants are hierarchical. Our model predicts p -> e^+, K^0 has larger decay width than that of p -> mu^+, K^0.