ScalingStacks

Proposition 5.53 . [02UQ]

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Proposition 5.53.

Let Σ\Sigma be a complete fan in NℝN_{\mathbb{R}} and let Π\Pi be a complete SCR polyhedral complex in NℝN_{\mathbb{R}} with Σ=rec⁡(Π)\Sigma=\operatorname{rec}(\Pi).

  1. (1)

    Let XΣ,KX_{\Sigma,K} and XΣ,HX_{\Sigma,H} denote the toric varieties defined by Σ\Sigma over KK and HH respectively. Then

    XΣ,H=Spec⁡(H)×XΣ,K.X_{\Sigma,H}=\operatorname{Spec}(H)\times X_{\Sigma,K}.

    Moreover there is a commutative diagram

    XΣ,Han\textstyle{X_{\Sigma,H}^{{\text{\rm an}}}\ignorespaces\ignorespaces\ignorespaces\ignorespaces\ignorespaces\ignorespaces\ignorespaces\ignorespaces}ρΣ,H\scriptstyle{\rho_{\Sigma,H}}XΣ,Kan\textstyle{X^{{\text{\rm an}}}_{\Sigma,K}\ignorespaces\ignorespaces\ignorespaces\ignorespaces}ρΣ,K\scriptstyle{\rho_{\Sigma,K}}XΣ​(ℝ≥0),\textstyle{X_{\Sigma}(\mathbb{R}_{\geq 0}),}

    where the horizontal map is induced by the restriction of seminorms.

  2. (2)

    Let Π′\Pi^{\prime} be the polyhedral complex in NℝN_{\mathbb{R}} obtained from Π\Pi by applying a homothety of ratio eH/Ke_{H/K}. Then

    𝒳Π′,H∘=Nor⁡(Spec⁡(H∘)×𝒳Π,K∘),{\mathcal{X}}_{\Pi^{\prime},{H}^{\circ}}=\operatorname{Nor}(\operatorname{Spec}(H^{\circ})\times{\mathcal{X}}_{\Pi,K^{\circ}}),

    where Nor\operatorname{Nor} denotes the normalization of a scheme.

  3. (3)

    Let ψ\psi be a rational piecewise linear function on Π\Pi and denote Ψ=rec⁡(ψ)\Psi=\operatorname{rec}(\psi). Let L=𝒪⁡(DΨ)L=\mathcal{O}(D_{\Psi}) be the line bundle on XΣ,KX_{\Sigma,K} determined by Ψ\Psi and let ∥⋅∥\|\cdot\| be the metric on LanL^{{\text{\rm an}}} determined by ψ\psi. Let L′L^{\prime} be the line bundle obtained by base change and ∥⋅∥′\|\cdot\|^{\prime} the metric obtained by inverse image. Then

    ψ∥⋅∥′(u)=(ψeH/K)(u)=eH/Kψ(eH/K−1u).\psi_{\|\cdot\|^{\prime}}(u)=(\psi e_{H/K})(u)=e_{H/K}\psi(e_{H/K}^{-1}u).
  4. (4)

    There is a commutative diagram

    XΣ,Han\textstyle{X_{\Sigma,H}^{{\text{\rm an}}}\ignorespaces\ignorespaces\ignorespaces\ignorespaces}XΣ,Kan\textstyle{X^{{\text{\rm an}}}_{\Sigma,K}}XΣ​(ℝ≥0).\textstyle{X_{\Sigma}(\mathbb{R}_{\geq 0})\ignorespaces\ignorespaces\ignorespaces\ignorespaces\ignorespaces\ignorespaces\ignorespaces\ignorespaces.}θΣ,H\scriptstyle{\theta_{\Sigma,H}}θΣ,K\scriptstyle{\theta_{\Sigma,K}}

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