  We study the possibility that supersymmetry is broken via a gaugino
condensate in four dimensional string theories. We derive an effective
low-energy theory describing the Goldstone mode associated with the R-symmetry
breaking driven by gaugino condensation and show that this gives a description
of gaugino condensation equivalent, at tree level, to other effective
Lagrangian approaches based on the symmetries of the theory. A study of the
mass gap equation shows that non-perturbative effects favour the appearance of
a gaugino condensate. By minimizing the effective potential describing both the
condensate and the moduli determining the gauge coupling constant and radius of
compactification we show that large hierarchy may occur between the gravitino
mass and the Planck mass with the existence of only one gaugino condensate.
Associated with this is a determination of the fine structure constant and the
compactification scale.

High Energy Physics - Phenomenology