ScalingStacks

Proof. [031E]

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Proof.

Recall that thanks to Lemma 4.7, on B×ℂn−mB\times\mathbb{C}^{n-m} we can write

λt∗​p∗​T−σ∗​ω~t−p∗​(ωS​F+f∗​ω)=Et,\lambda_{t}^{*}p^{*}T_{-\sigma}^{*}\tilde{\omega}_{t}-p^{*}(\omega_{SF}+f^{*}\omega)=E_{t},

where the error term EtE_{t} is a (1,1)(1,1)-form that goes to zero smoothly on compact sets. From (4.8) we also have that

Et=λt∗​p∗​(T−σ∗​ω~t−f∗​ω−t​ωS​F).E_{t}=\lambda_{t}^{*}p^{*}(T_{-\sigma}^{*}\tilde{\omega}_{t}-f^{*}\omega-t\omega_{SF}).

If we restrict the form T−σ∗​ω~t−f∗​ω−t​ωS​FT_{-\sigma}^{*}\tilde{\omega}_{t}-f^{*}\omega-t\omega_{SF} to a fiber MyM_{y} and divide by tt we get

Ett|{y}×ℂn−m=λt∗​p∗​(T−σ∗​ω~t|Myt−ωS​F,y)\frac{E_{t}}{t}\bigg|_{\{y\}\times\mathbb{C}^{n-m}}=\lambda_{t}^{*}p^{*}\left(\frac{T_{-\sigma}^{*}\tilde{\omega}_{t}|_{M_{y}}}{t}-\omega_{SF,y}\right)

Pulling back this via the map λ1/t\lambda_{1/t} (the inverse of λt\lambda_{t}) we get

λ1/t∗​Ett|{y}×ℂn−m=p∗​(T−σ∗​ω~t|Myt−ωS​F,y).\frac{\lambda_{1/t}^{*}E_{t}}{t}\bigg|_{\{y\}\times\mathbb{C}^{n-m}}=p^{*}\left(\frac{T_{-\sigma}^{*}\tilde{\omega}_{t}|_{M_{y}}}{t}-\omega_{SF,y}\right).

Explicitly we have λ1/t​(y,z)=(y,z​t)\lambda_{1/t}(y,z)=(y,z\sqrt{t}), which implies that λ1/t∗​d​zi=t​d​zi\lambda_{1/t}^{*}dz^{i}=\sqrt{t}dz^{i}, and so

λ1/t∗​Ett|{y}×ℂn−m​(y,z)=Et|{y}×ℂn−m​(y,z​t),\frac{\lambda_{1/t}^{*}E_{t}}{t}\bigg|_{\{y\}\times\mathbb{C}^{n-m}}(y,z)=E_{t}\bigg|_{\{y\}\times\mathbb{C}^{n-m}}(y,z\sqrt{t}),

which goes to zero smoothly as tt approaches zero, uniformly in yy. It follows that T−σ∗​ω~t|Myt\frac{T_{-\sigma}^{*}\tilde{\omega}_{t}|_{M_{y}}}{t} converges smoothly to ωS​F,y\omega_{SF,y}, and the convergence is uniform as yy varies on compact sets of N\f⁡(S)N\backslash f(S). Pulling back via TσT_{\sigma}, and using the fact that Tσ∗​ωS​F,y=ωS​F,yT_{\sigma}^{*}\omega_{SF,y}=\omega_{SF,y}, we see that also ω~t|Myt\frac{\tilde{\omega}_{t}|_{M_{y}}}{t} converges smoothly to ωS​F,y\omega_{SF,y}, as desired. ∎

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