Chiral symmetry from type IIA branes

We propose a mechanism in which, using an 8-brane, a 6-brane ends on an NS-brane in type IIA superstring theory. We use this mechanism to construct N = 1 supersymmetric gauge theories in four dimensions with chiral matter localized in different points in space. Anomaly cancelation for the gauge theories is satisfied by requiring RR charge conservation for the various type IIA fields. The construction allows us to study a curious phase transition in which the number of flavors in supersymmetric QCD depends on the value of the ten-dimensional cosmological constant. These phenomena are related to the fact that every time a D8-brane crosses an NS-brane, a D6-brane is created in between them. (C) 1998 Elsevier Science B.V.