2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/47178Much curent theoretical analysis is based on the hypothesis that the physics beyond the Standard Model is a consequence of new principles that occur at the Planck scale. The question arises whether such principles can ever be directly tested. We show here that for a significant class of models, hypotheses made at the string or Planck scale can indeed be directly tested to a relatively high degree of precision by linear colliders. Three classes of models are examined: those with universal SUSY soft breaking at the string scale, those with a horizontal symmetry at the string or Planck scale, and simple Calabi-Yau superstring models with dilaton and moduli SUSY breaking. (Invited talk at Orbis97.)latex, 11 pages; invited talk at Orbis Scientiae 97, Miami Beach, FLHigh Energy Physics - Phenomenologytext