ScalingStacks

Proof. [027B]

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Proof.

First we assume that hh is semipositive. By using Proposition 3.10, we can find a positive integer nn such that L⊗nL^{\otimes n} is generated by global sections and

|.|hn​(x)≤|.|hnquot​(x)≤en​ϵ/2​|.|hn​(x)|\raisebox{1.72218pt}{.}|_{h^{n}}(x)\leq|\raisebox{1.72218pt}{.}|^{\mathrm{quot}}_{h^{n}}(x)\leq e^{n\epsilon/2}|\raisebox{1.72218pt}{.}|_{h^{n}}(x)

for all x∈Xanx\in X^{\mathrm{an}}. On the other hand, there is s∈H0​(X,L⊗n)κ^​(x)∖{0}s\in H^{0}(X,L^{\otimes n})_{\hat{\kappa}(x)}\setminus\{0\} such that ‖s‖hn,κ^​(x)≤en​ϵ/2​|s|hnquot​(x)\|s\|_{h^{n},\hat{\kappa}(x)}\leq e^{n\epsilon/2}|s|^{\mathrm{quot}}_{h^{n}}(x). Thus,

‖s‖hn,κ^​(x)≤en​ϵ/2​|s|hnquot​(x)≤en​ϵ​|s|hn​(x).\|s\|_{h^{n},\hat{\kappa}(x)}\leq e^{n\epsilon/2}|s|^{\mathrm{quot}}_{h^{n}}(x)\leq e^{n\epsilon}|{s}|_{h^{n}}(x).

Next we consider the converse. For a positive integer mm, there is a positive integer eme_{m} such that, for any x∈Xanx\in X^{\mathrm{an}}, we can find s∈H0​(X,L⊗em)κ^​(x)∖{0}s\in H^{0}(X,L^{\otimes e_{m}})_{\hat{\kappa}(x)}\setminus\{0\} with ‖s‖hem,κ^​(x)≤eem/m​|s|hem​(x)\|s\|_{h^{e_{m}},\hat{\kappa}(x)}\leq e^{e_{m}/m}|s|_{h^{e_{m}}}(x). Clearly L⊗emL^{\otimes e_{m}} is generated by global sections. Moreover,

|s|hem​(x)≤|s|(H0​(X,L⊗em),‖.‖hem)quot​(x)≤eem/m​|s|hem​(x),|s|_{h^{e_{m}}}(x)\leq|s|^{\mathrm{quot}}_{(H^{0}(X,L^{\otimes e_{m}}),\|\raisebox{1.20552pt}{.}\|_{h^{e_{m}}})}(x)\leq e^{e_{m}/m}|s|_{h^{e_{m}}}(x),

that is,

0≤1em​log⁡(|.|(H0​(X,L⊗em),‖.‖hem)quot​(x)|.|hem​(x))≤1m.0\leq\frac{1}{e_{m}}\log\left(\frac{|\raisebox{1.72218pt}{.}|^{\mathrm{quot}}_{(H^{0}(X,L^{\otimes e_{m}}),\|\raisebox{1.20552pt}{.}\|_{h^{e_{m}}})}(x)}{|\raisebox{1.72218pt}{.}|_{h^{e_{m}}}(x)}\right)\leq\frac{1}{m}.

Thus hh is semipositive. ∎

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