On open/closed string duality

It was recently shown, using the AdS/CFT correspondence, that the low energy effective action of a large N open string theory satisfies a holographic RG flow equation closely related to the Hamilton-Jacobi equation of 5-d supergravity. In this paper we re-obtain the same flow equation in the dual regime of small 't Hooft coupling λ ≪ 1. Our derivation makes use of the conformal equivalence between planar open string diagrams and closed string tree diagrams. This equiva-lence can be viewed as a microscopic explanation of the open/closed string duality that underlies the AdS/CFT correspondence.