The strong coupling, unification, and recent data

Abstract

The prediction of the strong coupling assuming (supersymmetric) coupling constant unification is reexamined. We find, using the new electroweak data, $α_{s}(M_{Z}) \approx 0.129 \pm 0.010$. The implications of the large $α_{s}$ value are discussed. The role played by the $Z$ beauty width is stressed. It is also emphasized that high-energy (but not low-energy) corrections could significantly diminish the prediction. However, unless higher-dimension operators are assumed to be suppressed, at present one cannot place strong constraints on the super-heavy spectrum. Non-leading electroweak threshold corrections are also discussed.