Lowering αs by flipping SU(5)

We show that the prediction for αs(Mz) in flipped SU(5) is naturally lower than in minimal SU(5), and that the former can accommodate the full range of αs(Mz) presently allowed by experiment. Our computations include two-loop (δ2loop) and light (δlight) and heavy (δheavy) threshold effects. Unlike minimal SU(5), in flipped SU(5), the heavy threshold effects can naturally decrease the predicted value of αs(Mz). We also show that the value of the proton lifetime into the dominant channel p → e+ π0 is within the observable range at SuperKamiokande, and should discriminate against minimal supersymmetric SU(5), where the dominant mode is p → νK+.