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arXiv 2112.10312math.AG
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关于霍赫希尔德同调和半正交分解的几点注记

Some remarks of Hochschild homology and semi-orthogonal decompositions

Xun Lin

摘要:

给定一个非平凡的半正交分解$\Perf(\X)=\langle \mathcal{A},\mathcal{B}\rangle$,并假设$ω_{\X}$的基轨迹是一个真闭子集,Kotaro Kawatani和Shinnosuke Okawa证明了所有具有$\x\notin \mathsf{Bs}\vert ω_{\X}\vert$的摩天大楼层$\k(\x)$属于且仅属于其中一个分支.很自然会问它是哪一个,以及我们是否可以通过某些线性不变量来确定它。本文利用有支撑的凝聚层的导出范畴的霍赫希尔德同调证明了如果一个分量的$-\n^þ$霍赫希尔德同调为非零,则我们所考虑的摩天大楼层属于这类分量,这一证明最初由Dmitrii Pirozhkov \cite [引理5.3]{pirozhkov 2020 admissible}证明.进一步证明了Kuznetsov提出的一个猜想,即在对Calabi-Yau范畴作进一步假设的情况下,对某个射影光滑簇$\X$,将$\Perf(\X)$($\dim \X=\n$)的$\n$-Calabi-Yau可容许子范畴分类.最后,我们注意到具有支撑的导出范畴的加法不变量可以为半正交分解提供更多的线性障碍。

英文摘要:

Given a nontrivial semi-orthogonal decomposition $\Perf(\X)=\langle \mathcal{A},\mathcal{B}\rangle$, and assume that the base locus of $ω_{\X}$ is a proper closed subset, it was proved by Kotaro Kawatani and Shinnosuke Okawa that all skyscraper sheaves $\k(\x)$ with $\x\notin \mathsf{Bs}\vert ω_{\X}\vert$ belong to exactly one and only one of the components. It is natural to ask which one it is, and whether we can determine this by certain linear invariants. In this note we use Hochschild homology of derived category of coherent sheaves with support to provide another proof that if the $-\n^þ$ Hochschild homology of a component is nonzero, then the skyscraper sheaves we consider above belong to such component, which was originally proved by Dmitrii Pirozhkov \cite[Lemma 5.3]{pirozhkov2020admissible}. Furthermore, we prove a conjecture proposed by Kuznetsov about classifying $\n$-Calabi-Yau admissible subcategory of $\Perf(\X)$ ($\dim \X=\n$) for certain projective smooth variety $\X$ if we put more assumptions to the Calabi-Yau categories. Finally we remark that the additive invariants of derived category with support could provide more linear obstructions to semi-orthogonal decompositions.

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