He’s conjecture on connected components of affine Deligne–Lusztig varieties

Let GG be the reductive group, let bG(F˘)b\in G(\breve{F}) and let μ\mu be a cocharacter, with associated affine Deligne–Lusztig variety XμKp(b)X^{\mathcal{K}_p}_\mu(b). Write π0(XμKp(b))\pi_0(X^{\mathcal{K}_p}_\mu(b)) for its set of connected components, and let ωG\omega_G be the map to the subset cb,μπ1(G)Iφc_{b,\mu}\pi_1(G)_I^\varphi of the coinvariants of the algebraic fundamental group π1(G)\pi_1(G) under inertia II and Frobenius φ\varphi. Assume that (b,μ)(b,\mu) is HN-irreducible. He’s conjecture. The map

ωG:π0(XμKp(b))cb,μπ1(G)Iφ\omega_G:\pi_0(X^{\mathcal{K}_p}_\mu(b))\to c_{b,\mu}\pi_1(G)_I^\varphi

is bijective. The connected components of affine Deligne–Lusztig varieties are an important part of understanding their geometric structure. The statement is presented as a conjecture suggested by X. He; its resolution is not specified in the supplied text.

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Primary source

Ian Gleason, Dong Gyu Lim and Yujie Xu, “The connected components of affine Deligne–Lusztig varieties”, arXiv:2208.07195 (2025).

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