The positive-depth Lusztig induction and Kim–Yu type structure conjecture

Assume G\mathbf{G}' is a twisted Levi subgroup of G\mathbf{G} containing T\mathbf{T}. Let α\alpha be any representation of Gr(Fq)\mathbb{G}'_r(\mathbb{F}_q) of depth <r<r, and let ϕ ⁣:Gr(Fq)Q×\phi\colon \mathbb{G}'_r(\mathbb{F}_q)\to\overline{\mathbb{Q}}_\ell^{\times} be a (G,G)(\mathbf{G}',\mathbf{G})-generic character of depth rr. Write RGrGrR_{\mathbb{G}'_r}^{\mathbb{G}_r} for positive-depth Lusztig induction, K0Gx,0K_0\subseteq G_{\mathbf{x},0} for the relevant compact subgroup, and let ραϕ\rho_{\alpha\otimes\phi} be the representation constructed in Yu's construction in the context of Kim–Yu types. Positive-depth Lusztig induction conjecture. One has

RGrGr(αϕ)=IndK0Gx,0(ϵG/Gραϕ),\left|R_{\mathbb{G}'_r}^{\mathbb{G}_r}(\alpha\otimes\phi)\right|=\operatorname{Ind}_{K_0}^{G_{\mathbf{x},0}}\left(\epsilon^{G/G'}\otimes\rho_{\alpha\otimes\phi}\right),

where ϵG/G\epsilon^{G/G'} is the FKS twist. This conjectural identity is intended to relate positive-depth Lusztig induction directly to the construction of Kim–Yu types; it is motivated by Howe factorizations, positive-depth character sheaves, and the known successive-induction structure of the modified Deligne–Lusztig representation, but no resolution is supplied here.

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Primary source

Charlotte Chan and Masao Oi, “Green functions for positive-depth Deligne–Lusztig induction”, arXiv:2506.04449 (2025).

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