Stratified cohomology conjecture for Deligne–Lusztig varieties

Let WW be the Weyl group, let wWw\in W, and let Yx(w˙)Y_x(\dot w) be the stratum defined by

Yx(w˙)={gU0B0xU0/U0g1F(g)U0w˙U0}.Y_x(\dot w)=\{gU_0\in B_0xU_0/U_0\mid g^{-1}F(g)\in U_0\dot wU_0\}.

For a GG-regular linear character ψ:U0O×\psi:U_0\to\mathcal{O}^{\times}, let Oψ\mathcal{O}_\psi be the associated OU0\mathcal{O}U_0-module. Stratified cohomology conjecture. There are isomorphisms in Db(OT0wF)D^b(\mathcal{O}{\mathbf{T}}_0^{wF}):

RHomOU0(RΓc(Yx(w˙),O),Oψ){OT0wFif x=wΔ,0otherwise.R\operatorname{Hom}\nolimits^\bullet_{\mathcal{O}U_0}(R\Gamma_c(Y_x(\dot w),\mathcal{O}),\mathcal{O}_\psi)\simeq \begin{cases} \mathcal{O}{\mathbf{T}}_0^{wF} & \text{if }x=w_\Delta,\\ 0 & \text{otherwise.} \end{cases}

This conjecture refines the torus case by specifying which strata contribute to the cohomology. The source proposes it as a refinement; no general proof or disproof is supplied.

Sources & referencesView supporting material

Primary source

Cédric Bonnafé and Raphaël Rouquier, “Coxeter orbits and modular representations”, arXiv:math/0511737 (2006).

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