Orlik's orbit-average conjecture for reverse operators on 1-standard gradings

Let g=iZg(i)\mathfrak g=\bigoplus_{i\in\mathbb Z}\mathfrak g(i) be a 11-standard Z\mathbb Z-grading, so that g(1)\mathfrak g(1) is a simple g(0)\mathfrak g(0)-module and the semisimple part of g(0)\mathfrak g(0) is g(0)~\widetilde{\mathfrak g(0)}. Let Δ(1)\Delta(1) be the associated weight poset, let XΔ(1)\mathfrak X_{\Delta(1)} be its reverse operator, and set

d1=max{ht(γ)γΔ(1)}.d_1=\max\{{\mathsf{ht}}(\gamma)\mid\gamma\in\Delta(1)\}.

Orlik's orbit-average conjecture. The following assertions hold: (i) ord(XΔ(1))=d1+1{\mathsf{ord}}(\mathfrak X_{\Delta(1)})=d_1+1; (ii) the average size of the antichains in every XΔ(1)\mathfrak X_{\Delta(1)}-orbit is

dimg(1)d1+1=#Δ(1)ord(XΔ(1));\frac{\dim\mathfrak g(1)}{d_1+1}=\frac{\#\Delta(1)}{{\mathsf{ord}}(\mathfrak X_{\Delta(1)})};

and (iii) the average size of the upper ideals in every XΔ(1)\mathfrak X_{\Delta(1)}-orbit is dimg(1)/2\dim\mathfrak g(1)/2.

These properties are supported by computations and are established in several special classes, but the general 1-standard case remains open.

Sources & referencesView supporting material

Primary source

Dmitri I. Panyushev, “Antichains in weight posets associated with gradings of simple Lie algebras”, arXiv:1411.7683 (2014).

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