Brane Configurations for Branes at Conifolds

We show that a set of type IIB D3 branes at a conifold singularity is T dual to a type IIA configuration of D4 branes stretched between two relatively rotated NS fivebranes. The T duality can be applied to a large family of other non-orbifold singularities. The four-dimensional N=1 field theories on the D3 brane world-volume can be easily described using the IIA brane configuration. These models include families of chiral theories continuously connected to the theories appearing in brane box models (or D3 branes at orbifold singularities). We propose that flop transitions between topologically different small resolutions of the singularities are related to the crossing of rotated NS fivebranes in the T dual picture, and thus to Seiberg's duality in one of the gauge factors. We also comment on the inclusion of orientifold planes in the IIA brane picture