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Proton Decay: Flipped vs Unflipped SU(5)

We analyze nucleon decay modes in a no-scale supersymmetric flipped SU(5) GUT model, and contrast them with the predictions for proton decays via dimension-6 operators in a standard unflipped supersymmetric SU(5) GUT model. We find that these GUT models make very different predictions for the ratios $Γ(p \to π^0 μ^+)/Γ(p \to π^0 e^+)$, $Γ(p \to π^+ \barν)/Γ(p \to π^0 e^+)$, $Γ(p \to K^0 e^+)/Γ(p \to π^0 e^+)$ and $Γ(p \to K^0 μ^+)/Γ(p \to π^0 μ^+)$, and that predictions for the ratios $Γ(p \to π^0 μ^+)/Γ(p \to π^0 e^+)$ and $Γ(p \to π^+ \barν)/Γ(p \to π^0 e^+)$ also differ in variants of the flipped SU(5) model with normal- or inverse-ordered light neutrino masses. Upcoming large neutrino experiments may have interesting opportunities to explore both GUT and flavour physics in proton and neutron decays.