Stapledon's integrality conjecture for equivariant Ehrhart series

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Let GG be a finite group acting on a lattice polytope P⊆RnP\subseteq\mathbb{R}^n. Let MM be the sublattice obtained by translating the affine span of PP to the origin, and let ρ:G→GL(M)\rho:G\to GL(M) be the induced representation. For g∈Gg\in G, let PgP^g be the fixed-point polytope and let MgM^g be the sublattice of MM fixed by gg. Define ind⁡(P)\operatorname{ind}(P) as the smallest positive integer kk such that the affine span of kPkP contains a lattice point, and define det⁡(I−ρ(g))(Mg)⊥\det(I-\rho(g))_{(M^g)^\perp} using the restriction of ρ(g)\rho(g) to (Mg)⊥(M^g)^\perp. Stapledon's integrality conjecture. For every g∈Gg\in G,

H∗[1](g)=dim⁡(Pg)!⋅vol⁡(Pg)⋅det⁡(I−ρ(g))(Mg)⊥ind⁡(Pg)H^*[1](g)=\frac{\dim(P^g)!\cdot\operatorname{vol}(P^g)\cdot\det(I-\rho(g))_{(M^g)^\perp}}{\operatorname{ind}(P^g)}

is a non-negative integer. This conjecture predicts an arithmetic integrality property of the evaluation of the equivariant Ehrhart series and is part of Stapledon's program; the supplied text does not give a general resolution.

References

Primary source

Federico Ardila, Mariel Supina and Andrés R. Vindas-Meléndez, “The equivariant Ehrhart theory of the permutahedron”, arXiv:1911.11159 (2020).

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