SUPERHEAVY SPECTRUM AND SUPERSYMMETRIC GRAND UNIFICATION

We examine in detail the effect of the superheavy particle spectrum on the claim that recent data from CERN LEP are consistent with a SUSY SU(5) grand unified theory (GUT) whose superparticle spectrum is characterized by a single scale M(S) of approximately 1 TeV, and has three couplings unifying at a scale mu = M(V). Using the most recent LEP determination of alpha(s), 0.125+/-0.005, we find that SUSY unification requires that M(S) < 100 GeV. Larger values of M(S) can be accommodated by assuming that SIGMA, a multiplet transforming as the adjoint of SU(5), has a mass 8 to 12 orders of magnitude below the GUT scale, with the GUT scale close to or even above the Planck scale. Larger values of alpha(s), with unification below the Planck scale, may be accommodated only by breaking the degeneracy of the color octet and weak triplets of the SIGMA multiplet, but this splitting appears in SUSY SU(5) GUT's only as a gravitational effect in the form of nonrenormalizable operators.