Structure Constants of a Single Trace Operator and Determinant Operators from Hexagon.

We study the structure constant of a single trace operator and two determinant operators in ${\cal N}=4$ super Yang-Mills theory. Holographically such a quantity corresponds to the interaction vertex between a closed string and two open strings attached to the spherical $D$-branes. Relying on diagrammatic intuition, we conjecture that the structure constant at the finite coupling is nicely written by the hexagon form factors. Precisely we need to prepare two hexagon twist operators and appropriately glue edges together by integrating mirror particles contributions and by contracting boundary states. The gluing generates the worldsheet for a closed string and two open strings attached to the $D$-branes. At the weak coupling, the asymptotic expression simply reduces to sum over all possible partitions not only for the edge related to the closed string but also for the edges representing the half of the open string together with reflection effects for the opposite open string edges. We test the conjecture by directly computing various tree level structure constants. The result is nicely matched with our conjecture.