ScalingStacks

3.1 Calabi-Yau measure [008I]

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3.1 Calabi-Yau measure

The Calabi-Yau measure (2) is studied thoroughly in [3], but it is illustrative to recall it explicitly on a semistable snc model 𝒳\mathcal{X}. The discussion is local on the base, and we will follow the notations of section 2, e.g. the components of the central fibre are denoted as EiE_{i} for i∈Ii\in I.

The canonical divisor K𝒳=βˆ‘iai​EiK_{\mathcal{X}}=\sum_{i}a_{i}E_{i} is supported on the central fibre, since KXK_{X} is trivialised. Multiplying Ξ©\Omega by a power of tt, which does not change d​μtd\mu_{t}, we may assume min⁑ai=0\min a_{i}=0. In the local coordinates around EJE_{J} away from the deeper strata,

Ξ©=fJβ€‹βˆ0pziai​d​zi∧∏p+1nd​zj\Omega=f_{J}\prod_{0}^{p}z_{i}^{a_{i}}dz_{i}\wedge\prod_{p+1}^{n}dz_{j}

for some nowhere vanishing local holomorphic function fJf_{J}. Since t=z0​…​zpt=z_{0}\ldots z_{p},

Ξ©t=fJ​z0a0​…​zpapβ€‹βˆ1pd​log⁑zi∧∏p+1nd​zj,\Omega_{t}=f_{J}z_{0}^{a_{0}}\ldots z_{p}^{a_{p}}\prod_{1}^{p}d\log z_{i}\wedge\prod_{p+1}^{n}dz_{j},

hence

βˆ’1n2​Ωt∧Ω¯t=|fJ|2​|z0|2​a0​…​|zp|2​apβ€‹βˆ1pβˆ’1​d​log⁑zi∧d​log⁑zi¯∧∏p+1nβˆ’1​d​zj∧d​zΒ―j.\sqrt{-1}^{n^{2}}\Omega_{t}\wedge\overline{\Omega}_{t}=|f_{J}|^{2}|z_{0}|^{2a_{0}}\ldots|z_{p}|^{2a_{p}}\prod_{1}^{p}\sqrt{-1}d\log z_{i}\wedge d\overline{\log z_{i}}\wedge\prod_{p+1}^{n}\sqrt{-1}dz_{j}\wedge d\overline{z}_{j}.

The total measure ∫Xtβˆ’1n2​Ωt∧Ω¯t\int_{X_{t}}\sqrt{-1}^{n^{2}}\Omega_{t}\wedge\overline{\Omega}_{t} is of the order O⁑(|log⁑|t||m)O(|\log|t||^{m}) where

m=max{|J|βˆ’1:EJβ‰ βˆ…,ai=0Β forΒ i∈J}.m=\max\{|J|-1:E_{J}\neq\emptyset,a_{i}=0\text{ for }i\in J\}.

Thus d​μtd\mu_{t} satisfies a uniform upper bound of class (ai)(a_{i}) (cf. (4)).

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