DETECTING PHYSICS AT THE POST-GRAND-UNIFIED-THEORY AND STRING SCALES BY LINEAR COLLIDERS

The ability of linear colliders to test physics at the post-GUT scale is investigated. Using current estimates of measurements available at such accelerators, it is seen that soft breaking masses can be measure d with errors of about (1-20)%. Three classes of models in the post-GU T region are examined: models with universal soft breaking masses at t he string scale, models with horizontal symmetry, and string models wi th Calabi-Yau compactifications. In each case, linear colliders would be able to test directly theoretical assumptions made at energies beyo nd the GUT scale to a good accuracy, distinguish between different mod els, and measure parameters that are expected to be predictions of str ing models.