quasicoherent sheaf


quasicoherent sheaf

Definition

  • A sheaf \({\mathcal{F}}\in {\mathsf{Sh}}(X; {}_{{\mathcal{O}}_X}{\mathsf{Mod}} )\) is quasicoherent if \(X\) is covered by open affine subsets \(U_{i}=\operatorname{Spec} A_{i}\) such that for each \(i\) there is an \(A_{i}\)-module \(M_{i}\) with \(\left.\mathcal{F}\right|_{U_{i}} \cong \widetilde{M}_{i}\), the sheaf associated to a module for \(M_i\).

  • \(\mathcal{F}\) is coherent if it is quasicoherent and each \(M_{i}\) is finitely generated.

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Notes

Reference: https://arxiv.org/pdf/1410.1716.pdf #resources/papers

  • A Noetherian scheme \(X\) can be reconstructed from \(X\) can be reconstructed from \({\mathsf{QCoh}}(X)\), see Gabriel 1962.
    • Idea: associate to an ringed space \(\operatorname{Spec}\mathsf{A}\) and show \begin{align*}X \underset{\mathsf{RingSp}}{\xrightarrow{\cong}} \operatorname{Spec}\mathsf{{\mathsf{QCoh}}(A)}\end{align*}
  • A smooth variety \(X\) can not generally be reconstructed from its ample bundle.
  • In 2002 Balmer reconstructs a Noetherian scheme from its perfect complexes.
    • Lurie 2006ish: some more general result?

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🗓️ Timeline
  • Prismatic cohomology

    Upshot: \(\mathsf{WCart}^{\operatorname{HT}}= {\mathbf{B}}W^* [F]\) is a classifying stack. quasicoherent sheaves on the left and representations of the (classifying stack of the) group scheme on the right. I.e. \({ \mathsf{D} }_{\operatorname{qc}}(\mathsf{WCart}^{\operatorname{HT}}) = {\mathbf{R}}(W^*[F])\).

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