LOW ALPHA(S) - HINTS OF NEW PHYSICS AT THE GUT SCALE

In a SUSY GUT having an extra reverse doublet-triplet splitting near t he GUT scale, where the mass of an extra doublet is greater than the m ass of an extra triplet by two orders of magnitude, a low prediction o f alpha(s) can be achieved through threshold corrections via the heavy scalars in the fundamental representations, making the prediction con sistent with the values being suggested by low energy measurements. We implement this mechanism in a SUSY SU(5) GUT minimally extended to su ppress Higgsino-mediated proton decay. We also point out that as a con sequence of this extension a natural scenario arises with a large hier archy in Yukawa couplings (lambda(t)/lambda(b) similar to 40). An expe rimental low value of alpha(s)(m(Z)) along with the nonobservation of dimension-five proton decay modes at the SuperKamiokande detector will favor such an extension of the SUSY SU(5) GUT over the minimal case.