ScalingStacks

Proof. [02DU]

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Proof.

Observe that ωn=E​d​λ\omega^{n}=Ed\lambda for some smooth density E≥0E\geq 0 which vanishes along the exceptional divisor of π\pi, thus

μ=f1​d​λ=f​ωn, where ​f=f1/E.\mu=f_{1}d\lambda=f\omega^{n},\text{ where }f=f_{1}/E.

Fix local coordinates (zi)1≤i≤n(z^{i})_{1\leq i\leq n} on a polydisk 𝔻⊂X\mathbb{D}\subset X and a local embedding F:V→ℂmF:V\to\mathbb{C}^{m}. Note that EE is comparable to |∂F∂z1∧…∧∂F∂z1|2≃∑i=1r|fi|2|\frac{\partial F}{\partial z^{1}}\wedge\ldots\wedge\frac{\partial F}{\partial z^{1}}|^{2}\simeq\sum_{i=1}^{r}|f_{i}|^{2}, fif_{i} being holomorphic on 𝔻\mathbb{D}. Therefore E∈Ll​o​c∞​(𝔻)E\in L^{\infty}_{loc}(\mathbb{D}) and E−α∈Ll​o​c1​(𝔻,d​λ)E^{-\alpha}\in L_{loc}^{1}(\mathbb{D},d\lambda) for some 0<α<10<\alpha<1.

Choose 0<α′<α0<\alpha^{\prime}<\alpha such that 1p+1α=1α′\frac{1}{p}+\frac{1}{\alpha}=\frac{1}{\alpha^{\prime}}. Then fα′=f1α′​E−α′f^{\alpha^{\prime}}=f_{1}^{\alpha^{\prime}}E^{-\alpha^{\prime}} is the product of a function in Lp/α′​(d​λ)L^{p/\alpha^{\prime}}(d\lambda) and a function in Lα/α′​(d​λ)L^{\alpha/\alpha^{\prime}}(d\lambda), hence it is in Ll​o​c1​(𝔻,d​λ)L^{1}_{loc}(\mathbb{D},d\lambda) by Hölder’s inequality. A second application of Hölder’s inequality yields

∫𝔻f1+ε​ωn=∫𝔻fϵ​f1​𝑑λ≤(∫𝔻fϵ​q​𝑑λ)1/q​(∫𝔻f1p​𝑑λ)1/p<+∞,\int_{{\mathbb{D}}}f^{1+\varepsilon}\omega^{n}=\int_{\mathbb{D}}f^{\epsilon}f_{1}d\lambda\leq\left(\int_{\mathbb{D}}f^{\epsilon q}d\lambda\right)^{1/q}\left(\int_{\mathbb{D}}f_{1}^{p}d\lambda\right)^{1/p}<+\infty,

where qq denotes the conjugate exponent to pp. This shows that f∈Lp′​(ωn)f\in L^{p^{\prime}}(\omega^{n}) if p′=1+ε>1p^{\prime}=1+\varepsilon>1 is chosen so small that ε​q<α′\varepsilon q<\alpha^{\prime}. ∎

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