A Landau-Ginzburg model for Lagrangian Grassmannians, Langlands duality and relations in quantum cohomology

In [Rie08], the second author defined a Landau-Ginzburg model for homogeneous spaces G/P, as a regular function on an affine subvariety of the Langlands dual group. In this paper, we reformulate this LG-model (X^,W_t) in the case of the Lagrangian Grassmannian LG(m) as a rational function on a Langlands dual orthogonal Grassmannian, in the spirit of work by R. Marsh and the second author [MR12] for type A Grassmannians. This LG model has some very interesting features, which are not visible in the type A case, to do with the non-triviality of Langlands duality. We also formulate a conjecture relating our superpotential with the quantum differential equations of LG(m). Finally, our expression for W_t also leads us to conjecture new formulas in the quantum Schubert calculus of LG(m).