Deriving the Simplest Gauge-String Duality -- I: Open-Closed-Open Triality

We lay out an approach to derive the closed string dual to the simplest possible gauge theory, a single hermitian matrix integral, in the conventional 't Hooft large $N$ limit. In this first installment of three papers, we propose and verify an explicit correspondence with a (mirror) pair of closed topological string theories. On the A-model side, this is a supersymmetric $SL(2, \mathbb{R})_1/U(1)$ Kazama-Suzuki coset (with background momentum modes turned on). The mirror B-model description is in terms of a Landau-Ginzburg theory with superpotential $W(Z)=\frac{1}{Z}+t_2Z$ and its deformations. We arrive at these duals through an "open-closed-open triality". This is the notion that two open string descriptions ought to exist for the same closed string theory depending on how closed strings manifest themselves from open string modes. Applying this idea to the hermitian matrix model gives an exact mapping to the Imbimbo-Mukhi matrix model. The latter model is known to capture the physical correlators of the $c=1$ string theory at self-dual radius, which, in turn, has the equivalent topological string descriptions given above. This enables us to establish the equality of correlators, to all genus, between single trace operators in our original matrix model and those of the dual closed strings. Finally, we comment on how this simplest of dualities might be fruitfully viewed in terms of an embedding into the full AdS/CFT correspondence.