ScalingStacks

Proof. [01I6]

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Proof.

We argue as in the last part of the proof of Theorem B.3. Let 𝒜∈Pic⁡(𝒳)\mathcal{A}\in\Pic(\mathcal{X}) be sufficiently ample to guarantee:

  • (i)

    π∗​𝒜−c​D\pi^{*}\mathcal{A}-cD is nef.

  • (ii)

    𝒜⊗Rq​π∗​ω𝒳′​(−⌊c​D⌋)\mathcal{A}\otimes R^{q}\pi_{*}\omega_{\mathcal{X}^{\prime}}\left(-\lfloor c\,D\rfloor\right) is globally generated on 𝒳\mathcal{X}.

  • (iii)

    Hp​(𝒳,𝒜⊗Rm​π∗​ω𝒳′​(−⌊c​D⌋))=0​ for all ​p≥1​ and ​m≥0H^{p}\left(\mathcal{X},\mathcal{A}\otimes R^{m}\pi_{*}\omega_{\mathcal{X}^{\prime}}\left(-\lfloor c\,D\rfloor\right)\right)=0\,\,\text{ for all }p\geq 1\text{ and }m\geq 0.

Note that the first condition can be achieved since −D-D is π\pi-globally generated. The degeneration of the Leray spectral sequence shows that

H0​(𝒳,𝒜⊗Rq​π∗​ω𝒳′​(−⌊c​D⌋))=Hq​(𝒳′,ω𝒳′​(−⌊c​D⌋)⊗π∗​𝒜),H^{0}\left(\mathcal{X},\mathcal{A}\otimes R^{q}\pi_{*}\omega_{\mathcal{X}^{\prime}}\left(-\lfloor c\,D\rfloor\right)\right)=H^{q}\left(\mathcal{X}^{\prime},\omega_{\mathcal{X}^{\prime}}\left(-\lfloor c\,D\rfloor\right)\otimes\pi^{*}\mathcal{A}\right),

which vanishes by Theorem B.3. It follows that 𝒜⊗Rq​π∗​ω𝒳′​(−⌊c​D⌋)=0\mathcal{A}\otimes R^{q}\pi_{*}\omega_{\mathcal{X}^{\prime}}\left(-\lfloor c\,D\rfloor\right)=0 by global generation, whence the result. ∎

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