Brane dynamics and chiral non-chiral transitions

We study brane realizations of chiral matter in N=1 supersymmetric gauge theories in four dimensions. A ''cross'' configuration which leads to ''flavor doubling'' is found to have a superpotential. The main example is realized using a special ''fork'' configuration. Many of the results are found by studying a SU x SU product gauge group first. The chiral theory is then an orientifold projection of the product gauge group. An interesting observation in the brane picture is that there are transitions between chiral and non-chiral models. These transitions are closely related to small instanton transitions in six dimensions. (orig.)