English

MV polytopes and reduced double Bruhat cells

Combinatorics 2023-01-26 v1 Algebraic Geometry

Abstract

When GG is a complex reductive algebraic group, MV polytopes are in bijection with the non-negative tropical points of the unipotent group of GG. By fixing ww from the Weyl group, we can define MV polytopes whose highest vertex is labelled by ww. We show that these polytopes are in bijection with the non-negative tropical points of the reduced double Bruhat cell labelled by w1w^{-1}. To do this, we define a collection of generalized minor functions Δγnew\Delta_\gamma^\text{new} which tropicalize on the reduced Bruhat cell to the BZ data of an MV polytope of highest vertex ww. We also describe the combinatorial structure of MV polytopes of highest vertex ww. We explicitly describe the map from the Weyl group to the subset of elements bounded by ww in the Bruhat order which sends uvu \mapsto v if the vertex labelled by uu coincides with the vertex labelled by vv for every MV polytope of highest vertex ww. As a consequence of this map, we prove that these polytopes have vertices labelled by Weyl group elements less than ww in the Bruhat order.

Keywords

Cite

@article{arxiv.2301.10627,
  title  = {MV polytopes and reduced double Bruhat cells},
  author = {Kathlyn Dykes},
  journal= {arXiv preprint arXiv:2301.10627},
  year   = {2023}
}

Comments

29 pages

R2 v1 2026-06-28T08:19:59.307Z