Low-energy signatures of semiperturbative unification

We consider the low-energy signatures of, and high-energy motivations for, scenarios of semiperturbative gauge coupling unification. Such scenarios can leave striking imprints on the low-energy sparticle spectrum, including novel gaugino mass ratios (including $M_2{/M}_1\approx 1$), substantial compression of the intragenerational squark-to-slepton mass ratios, and an overall lifting of scalar masses relative to the gauginos. We also demonstrate that the unification scale can be raised to $M_X\approx 4\times {10}^{17}$ GeV while still in the perturbative regime-close to the one-loop heterotic string scale. We employ a three-loop calculation of the running of the gauge couplings as a test of the perturbativity of the high-scale theory.