Lowering alpha_s by flipping SU(5)

Abstract

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 (${\delta }_{\mathrm{light}}$) and heavy (${\delta }_{\mathrm{heavy}}$) threshold effects. Unlike minimal SU(5), in flipped SU(5) the heavy threshold effects can naturally decrease the predicted value of ${\alpha }_s(M_Z)$. We also show that the value of the proton lifetime into the dominant channel $p\to e^{+}{\pi }^0$ is within the observable range at SuperKamiokande, and should discriminate against minimal supersymmetric SU(5), where the dominant mode is $p\to \bar{\nu }{K}^{+}$.

Comments: 11 pages, LaTeX, 2 figures (uuencoded)