A cubulation of the associahedron using a torus-equivariant degeneration of the brick variety

Abstract: We describe a mixed subdivision of the $(n-1)$-dimensional Loday associahedron into $(n-1)!$ maximal cells which are combinatorial cubes, and we show that the face poset of this subdivision is isomorphic to the face poset of the subdivision of the $1\times 2\times \dotsb \times (n-1)$ box into unit cubes. More generally, we describe mixed subdivisions of generalized associahedra into pieces which are Minkowski sums of Bruhat interval polytopes. Our subdivisions arise from a torus-equivariant embedded (in a product of flag varieties) degeneration of brick varieties into reduced unions of products of Richardson varieties. The subdivision of Loday's associahedron allows us to `embed' the 1-skeleton of the permutahedron in the boundary of the associahedron.