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 …