Cvetič, MirjamWeigand, Timo2023-05-232023-05-232008-06-242011-01-25https://repository.upenn.edu/handle/20.500.14332/42797We construct the first globally consistent semirealistic type I string vacua on an elliptically fibered manifold where the zero modes of the Euclidean D1-instanton sector allow for the generation of nonperturbative Majorana masses of an intermediate scale. In another class of global models, a D1-brane instanton can generate a Polonyi-type superpotential breaking supersymmetry at an exponentially suppressed scale.Physical Sciences and MathematicsPhysicsArticle