Faithfulness of tensoring by a quasi-coherent sheaf on Deligne–Mumford stacks

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Let XX be a quasi-separated Deligne–Mumford stack with generically trivial stabilizer. Let M∈QCoh⁡(X)\mathcal{M}\in \operatorname{QCoh}(X) and let α∈Br(X)\alpha\in \mathrm{Br}(X). Write QCoh⁡(X,α)\operatorname{QCoh}(X,\alpha) for the category of α\alpha-twisted quasi-coherent sheaves on XX. Tensor-action faithfulness conjecture. The functor

−⊗OXM ⁣:QCoh⁡(X,α)⟶QCoh⁡(X,α)-\otimes_{\mathcal{O}_{X}}\mathcal{M}\colon \operatorname{QCoh}(X,\alpha)\longrightarrow \operatorname{QCoh}(X,\alpha)

is naturally isomorphic to the identity functor id⁡\operatorname{id} if and only if M≅OX\mathcal{M}\cong \mathcal{O}_{X}. The statement would extend the corresponding faithfulness result from varieties to Deligne–Mumford stacks with generically trivial stabilizer; the source notes that the preceding results fail for some Deligne–Mumford stacks and asks whether examples with generically trivial stabilizers exist.

References

Primary source

Ting Gong, Yeqin Liu and Yu Shen, “Picard group action on the category of twisted sheaves”, arXiv:2508.09379 (2025).

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