Traditional Humphreys conjecture on support varieties of tilting modules

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Assume p>hp>h. Let Wext∅W_{\mathrm{ext}}^\varnothing be the set of elements of the extended affine Weyl group that are minimal in their cosets modulo WW, let T(λ)\mathsf T(\lambda) be the indecomposable tilting module of highest weight λ\lambda, let N\mathcal N be the nilpotent cone, and let VG1(M)V_{\mathbf G_1}(M) be the support variety of a G1\mathbf G_1-module. For w∈Wext∅w\in W_{\mathrm{ext}}^\varnothing, let CC be the GG-orbit in N\mathcal N corresponding via Lusztig's bijection to the two-sided cell containing ww.

Traditional Humphreys conjecture.

VG1(T(w∙0))=C‾.V_{\mathbf G_1}(\mathsf T(w\bullet0))=\overline C.

Humphreys originally presented this as a hypothesis or statement worthy of inquiry. The supplied text does not establish its resolution.

References

Primary source

Pramod N. Achar and Simon Riche, “Tilting modules for reductive algebraic groups: characters and support varieties”, arXiv:2511.05063 (2025).

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