On the equivalence of N=1 brane worlds and geometric singularities with flux

We consider Kaluza Klein reductions of M-theory on the Z_N orbifold of the spin bundle over S^3 along two different U(1) isometries. The first one gives rise to the familiar ``large N duality'' of the N=1 SU(N) gauge theory in which the UV is realized as the world-volume theory of N D6-branes wrapped on S^3, whereas the IR involves N units of RR flux through an S^2. The second reduction gives an equivalent version of this duality in which the UV is realized geometrically in terms of an S^2 of A_{N-1} singularities, with one unit of RR flux through the S^2. The IR is reached via a geometric transition and involves a single D6 brane on a lens space S^3/Z_N or, alternatively, a singular background (S^2\times R^4)/Z_N, with one unit of RR flux through S^2 and, localized at the singularities, an action of their stabilizer group in the U(1) RR gauge bundle, so that no massless twisted states occur. We also consider linear sigma-model descriptions of these backgrounds.