Symmetrizing polytopes and posets

Abstract

Motivated by the authors' work on permuto-associahedra, which can be considered as a symmetrization of the associahedron using the symmetric group, we introduce and study the $\mathfrak{G}$-symmetrization of an arbitrary polytope $P$ for any reflection group $\mathfrak{G}$. We show that the combinatorics, and moreover, the normal fan of such a symmetrization can be recovered from its refined fundamental fan, a decorated poset describing how the normal fan of $P$ subdivides the fundamental chamber associated to the reflection group $\mathfrak{G}$. One important application of our results is providing a way to approach the realization problem of a $\mathfrak{G}$-symmetric poset F, that is, the problem of constructing a polytope whose face poset is F. Instead of working with the original poset F, we look at its dual poset T (which is $\mathfrak{G}$-symmetric as well) and focus on a generating subposet Z of T, and reduce the problem to realizing Z as a refined fundamental fan.