ScalingStacks

Proposition 6.24 . [02WH]

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Proposition 6.24.

Let Σ\Sigma be a complete fan on NℝN_{\mathbb{R}} and σ∈Σ\sigma\in\Sigma a cone of codimension dd. To it, we have associated the dimension dd closed subvariety V⁡(σ)V(\sigma) and the closed immersion ισ:XΣ⁡(σ)→XΣ\iota_{\sigma}\colon X_{\Sigma(\sigma)}\to X_{\Sigma} whose image is V⁡(σ)V(\sigma). Let LL be a toric line on XΣX_{\Sigma} generated by global sections, ss a toric section, Ψ\Psi the corresponding support function, and ∥⋅∥\|\cdot\| an approachable toric metric on LanL^{{\text{\rm an}}}. As usual write L¯=(L,∥⋅∥){\overline{L}}=(L,\|\cdot\|). Then

hL¯tor⁡(V⁡(σ))=hισ∗​L¯tor⁡(XΣ⁡(σ))=(d+1)!​∫FσϑL¯,s​d​volM⁡(Fσ),\operatorname{h}^{\operatorname{tor}}_{{\overline{L}}}(V(\sigma))=\operatorname{h}^{\operatorname{tor}}_{\iota_{\sigma}^{\ast}{\overline{L}}}(X_{\Sigma(\sigma)})=(d+1)!\int_{F_{\sigma}}\vartheta_{{\overline{L}},s}\,\text{\rm d}\operatorname{vol}_{M(F_{\sigma})},

where FσF_{\sigma} is the face of ΔΨ\Delta_{\Psi} corresponding to σ\sigma, M⁡(Fσ)M(F_{\sigma}) is the lattice induced by MM on the linear space associated to FσF_{\sigma} and ισ∗​L\iota_{\sigma}^{\ast}L has the structure of toric line bundle of Proposition 4.34.

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