Intersecting brane landscape

Abstract

This thesis studies intersecting brane models, which are a class of quasi-realistic compactifications of string theory. Techniques are developed for exploring the complete space of intersecting brane models on an orientifold. The classification of all solutions for the widely-studied T6/Z2 x Z2 orientifold is made possible by computing all combinations of branes with negative tadpole contributions. This provides the necessary information to systematically and efficiently identify all models in this class with specific characteristics. In particular, all ways in which a desired group G can be realized by a system of intersecting branes (either as a subgroup or as the full gauge group) can be enumerated in polynomial time. For this orientifold we identify all distinct brane realizations of the gauge groups SU(3) x SU(2) and SU(3) x SU(2) x U(1) which can be embedded in any model which is compatible with the tadpole and SUSY constraints. We compute the distribution of the number of generations of "quarks" and find that 3 is neither suppressed nor particularly enhanced. The overall distribution of models is found to have a long tail. This tail in the distribution contains much of the diversity of low-energy physics structure. The tools developed in this thesis can be used to systematically explore the properties of a large class of string vacua, looking for patterns and correlations which may help in relating string theory to observed particle physics.