Lowering alpha(s) by flipping SU(5)

We show that the prediction for alpha(s)(M(z)) in flipped SU(5) is naturally lower than in minimal SU(5), and that the former can accommodate the full range of alpha(s)(M(z)) presently allowed by experiment. Our computations include two-loop (delta(2loop)) and light (delta(light)) and heavy (delta(heavy)) threshold effects. Unlike minimal SU(5), in flipped SU(5) the heavy threshold effects can naturally decrease the predicted value of a,(Mz). We also show that the value of the proton lifetime into the dominant channel p --> e(+) pi(0) is within the observable range at SuperKamiokande, and should discriminate against minimal supersymmetric SU(5), where the dominant mode is p --> <(nu)over bar K+>.