Lowering αs by flipping SU(5)

Abstract

We show that the prediction for α 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 α s ( M z ) presently allowed by experiment. Our computations include two-loop ( δ 2loop) and light ( δ light) and heavy ( δ heavy) threshold effects. Unlike minimal SU(5), in flipped SU(5), the heavy threshold effects can naturally decrease the predicted value of α s ( M z ). We also show that the value of the proton lifetime into the dominant channel p → e + π 0 is within the observable range at SuperKamiokande, and should discriminate against minimal supersymmetric SU(5), where the dominant mode is p → νK + .