Comparison conjecture for loop Deligne–Lusztig and Drinfeld cohomology

Let rr divide nn' and let θ ⁣:Th(Fq)Wh×(Fqn)Q×\theta \colon \mathbb T_h(\mathbb F_q) \cong \mathbb W_h^\times(\mathbb F_{q^n}) \to \overline{\mathbb Q}_\ell^\times be a character with trivial Gal(L/k)\operatorname{Gal}(L/k)-stabilizer. Let χ=θWh1(Fqn)\chi=\theta|_{\mathbb W_h^1(\mathbb F_{q^n})}, and assume that the stabilizer of χ\chi in Gal(L/k)\operatorname{Gal}(L/k) is the unique subgroup of index n0rn_0r. Comparison conjecture. There is an isomorphism of virtual Gh(Fq)\mathbb G_h(\mathbb F_q)-representations

Hc(Xh,Q)[θ]Hc(Xh(r),Q)[θ].H_c^*(X_h, \overline{\mathbb Q}_\ell)[\theta] \cong H_c^*(X_h^{(r)}, \overline{\mathbb Q}_\ell)[\theta].

This conjecture seeks to compare the cohomology of the loop Deligne–Lusztig variety XhX_h with that of its Drinfeld stratification. The paper presents supporting evidence, but the conjecture is not stated as resolved.

Sources & referencesView supporting material

Primary source

Charlotte Chan and Alexander B. Ivanov, “The Drinfeld stratification for GL_n”, arXiv:2001.06600 (2020).

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