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, Ms=MWMPlanck∼1011 GeV, then the notorious hierarchy, MW/MPlanck∼10−16, can be explained using only Mc/Ms∼0.01∼αGUT as small input parameters, where Mc 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 MW/MPlanck=12αGUT2(Mc/Ms)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 Ms; (ii) a natural axionic solution to the strong-CP problem with a phenomenologically-acceptable Peccei–Quinn scale; (iii) experimentally-interesting neutrino masses, and more.