The Problem of α_s in Supersymmetric Unified Theories

It is shown that in SO(10) there is a general connection between the suppression of higgsino mediated proton decay and the value of $\alpha_s$. However, agreement with the experimental value of $\alpha_s$ can be obtained if there are relatively large negative threshold corrections to $\alpha_s$ coming from superheavy split multiplets. It is shown that such split multiplets can arise in SO(10) without fine-tuning of parameters.