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Intersecting brane worlds—a path to the standard model?

In this paper we describe the general geometrical framework of brane world constructions in orientifolds of type IIA string theory with D6-branes wrapping 3-cycles in a Calabi–Yau 3-fold. These branes generically intersect at points on the internal space, and the patterns of intersections govern the chiral fermion spectra. We discuss how the open string spectra in intersecting brane models are constructed, how the standard model can be embedded, and also how supersymmetry can be realized in this class of string vacua. After the general considerations we restrict the discussion to the case of orbifold backgrounds with intersecting D6-branes and to the quintic Calabi–Yau manifold. Then, we discuss parts of the effective action of intersecting brane world models. Specifically, from the Born–Infeld action of the wrapped D-branes we compute the tree-level, D-term scalar potential, which is important for the stability of the considered backgrounds as well as for questions related to supersymmetry breaking. Second, we review the recent computation concerning gauge coupling unification and also concerning one-loop gauge threshold corrections in intersecting brane world models. Finally, we also discuss some aspects of proton decay in intersecting brane world models.