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

Let XX be a quasi-separated Deligne–Mumford stack with generically trivial stabilizer. Let MQCoh(X)\mathcal{M}\in \operatorname{QCoh}(X) and let αBr(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 MOX\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.

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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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