Precision Corrections to Supersymmetric Unification

We compute the full set of weak-scale gauge and Yukawa threshold corrections in the minimal supersymmetric standard model, including all finite (non-logarithmic) corrections, which we show to be important. We use our results to examine the effects of unification-scale threshold corrections in the minimal and missing-doublet SU(5) models. We work in the context of a unified mass spectrum, with scalar mass M_0 and gaugino mass M_1/2, and find that in minimal SU(5) with squark masses less than one TeV, successful gauge and Yukawa coupling unification requires M_1/2 << M_0 and M_0 \simeq 1 TeV. In contrast, we find that the missing-doublet model permits gauge and Yukawa unification for a wide range of supersymmetric masses.