Comparison conjecture for loop Deligne–Lusztig and Drinfeld cohomology

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Let rr divide n′n' and let θ ⁣:Th(Fq)≅Wh×(Fqn)→Q‾ℓ×\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=θ∣Wh1(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‾ℓ)[θ]≅Hc∗(Xh(r),Q‾ℓ)[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.

References

Primary source

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

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