Toric degenerations of integrable systems on Grassmannians and polygon spaces

Abstract

We introduce a completely integrable system on the Grassmannian of 2-planes in an $n$-space associated with any triangulation of a polygon with $n$ sides, and we compute the potential function for its Lagrangian torus fiber. The moment polytopes of this system for different triangulations are related by an integral piecewise-linear transformation, and the corresponding potential functions are related by its geometric lift in the sense of Berenstein and Zelevinsky.