Strings at the intermediate scale or is the Fermi scale dual to the Planck scale?

We show that if the string scale is identified with the intermediate scale, M-s = root MWMPlanck similar to 10(11) GeV, then the notorious hierarchy, M-W/M-Planck similar to 10(-16), can be explained using only M-c/M-s similar to 0.01 similar to alpha(GUT) as small input parameters, where M-c is the compactification scale. This is possible for weakly-coupled Type-I open-string vacua if the observed world is assumed to live in an N = 1 supersymmetric 3-brane sector coupled to a separate, hidden, 3-brane world which breaks supersymmetry, because for such a model M-W/M-Planck = 1/2 alpha(GUT)(2) (M-c/M-s)(6). We discuss some of the phenomenological issues presented by such an intermediate-scale string, showing that its benefits include: (i) the possibility of logarithmic gauge-coupling unification of the SM couplings at M-s; (ii) a natural axionic solution to the strong-CP problem with a phenomenologically-acceptable Peccei-Quinn scale; (iii) experimentally-interesting neutrino masses, and more. (C) 1999 Published by Elsevier Science B.V. All rights reserved.