Pome

Theorem 20.2.347EFDFA26519B

Theorem 20.2.34.7EFDFA26519B If $Y\not\subseteq \operatorname{nn}(\alpha )$, then

3C4F71AC116E 20.2.35
\begin{equation} \begin{aligned} \operatorname{vol}_{X|Y}(\alpha ) & = \lim _{\epsilon \to 0+}\int _ Y \Bigl (\theta |_ Y + \epsilon \omega |_ Y + \mathrm{dd}^{\mathrm{c}}V_{\theta + \epsilon \omega }|_ Y\Bigr )^ m\\ =& \lim _{\epsilon \to 0+}\int _ Y \left(\theta |_ Y + \epsilon \omega |_ Y + \mathrm{dd}^{\mathrm{c}}\operatorname{Tr}_ Y^{\theta + \epsilon \omega }(V_{\theta + \epsilon \omega }) \right)^ m \\ & =\int _ Y \left( \theta |_ Y+\mathrm{dd}^{\mathrm{c}}\operatorname{Tr}_ Y^{\theta }(V_{\theta }) \right)^ m, \end{aligned} \end{equation}

where the last term is understood as $0$ if $\operatorname{Tr}_ Y^{\theta }(V_{\theta })$ is not defined.

Proof. Since $\nu (V_\theta , Y)=0$, we have $Y\not\subseteq \operatorname{nK}(\alpha +\epsilon \{ \omega \} )$ for all $\epsilon >0$. Therefore, by (20.2.31) and (20.2.33), only the last equality of (20.2.35) needs to be argued.

Thanks to 16.9.50, we have

\[ V_{\theta +\epsilon \omega }\xrightarrow {d_ S}V_{\theta } \]

as $\epsilon \to 0+$.

Therefore, using proposition 20.2.22, we find

\[ \operatorname{Tr}_ Y\left( V_{\theta +\epsilon \omega } \right) \xrightarrow {d_ S} \operatorname{Tr}_ Y\left(V_{\theta }\right). \]

Set

\[ M\coloneqq \lim _{\epsilon _0\to 0+}\int _ Y \left(\theta |_ Y+\epsilon _0\omega |_ Y\right)^ m_{\operatorname{Tr}_ Y^{\theta +\epsilon _0\omega }(V_{\theta })}. \]

By example 20.2.17, if $\operatorname{Tr}_ Y^{\theta }(V_{\theta })$ is defined, then

\[ M=\int _ Y (\theta |_ Y)^ m_{\operatorname{Tr}_ Y^{\theta }(V_{\theta })}, \]

whereas if $\operatorname{Tr}_ Y^{\theta }(V_{\theta })$ is not defined, then $M=0$. Thus $M$ is the last term of (20.2.35), with the convention made in the statement.

Thanks to theorem 16.9.30, for any $\epsilon _0>0$, we have

\[ \begin{aligned} \lim _{\epsilon \to 0+}\int _ Y \left(\theta |_ Y + \epsilon _0 \omega |_ Y\right)^ m_{\operatorname{Tr}_ Y^{\theta + \epsilon _0 \omega }(V_{\theta + \epsilon \omega })} & = \int _ Y (\theta |_ Y + \epsilon _0 \omega |_ Y)^ m_{\operatorname{Tr}_ Y^{\theta + \epsilon _0 \omega }(V_{\theta })}. \end{aligned} \]

By the definition of $M$, this implies the existence of $(\epsilon _ j)_{j>0}$ such that $0<\epsilon _ j<1/j$ and

6EEF71F49B54 20.2.36
\begin{equation} \lim _{j\to \infty }\int _ Y \left(\theta |_ Y + j^{-1}\omega |_ Y\right)^ m_{\operatorname{Tr}_ Y^{\theta + j^{-1} \omega }(V_{\theta + \epsilon _ j \omega }) } = M. \end{equation}

Moreover, for each $j>0$,

E74D68200A33 20.2.37
\begin{equation} \begin{aligned} \int _ Y \left(\theta |_ Y + j^{-1} \omega |_ Y\right)^ m_{\operatorname{Tr}_ Y^{\theta + j^{-1} \omega }(V_{\theta + \epsilon _ j \omega }) } \geq & \int _ Y \left(\theta |_ Y + \epsilon _ j \omega |_ Y\right)^ m_{\operatorname{Tr}_ Y^{\theta + \epsilon _ j\omega }(V_{\theta + \epsilon _ j \omega }) } \\ \geq & M. \end{aligned} \end{equation}

Indeed, the first inequality follows from the multi-linearity of the non-pluripolar products proposition 13.11.4 6. For the second one, if $M=0$ there is nothing to prove; if $M>0$, then example 20.2.17 shows that $\operatorname{Tr}_ Y^\theta (V_\theta )$ is defined, and the inequality follows from the multi-linearity of the non-pluripolar products proposition 13.11.4 6 and the monotonicity theorem proposition 16.8.22. Putting (20.2.36) and (20.2.37) together, it follows that

\[ \lim _{j\to \infty }\int _ Y \left(\theta |_ Y + \epsilon _ j \omega |_ Y\right)^ m_{\operatorname{Tr}_ Y^{\theta + \epsilon _ j \omega }(V_{\theta + \epsilon _ j \omega }) } = M. \]

Finally, since $\int _ Y \left(\theta |_ Y + \epsilon \omega |_ Y + \mathrm{dd}^{\mathrm{c}}\operatorname{Tr}_ Y^{\theta + \epsilon \omega }(V_{\theta + \epsilon \omega }) \right)^ m$ depends monotonically on $\epsilon >0$, we conclude that

\[ \lim _{\epsilon \to 0+}\int _ Y \left(\theta |_ Y + \epsilon \omega |_ Y + \mathrm{dd}^{\mathrm{c}}\operatorname{Tr}_ Y^{\theta + \epsilon \omega }(V_{\theta + \epsilon \omega }) \right)^ m=M. \]

This completes the proof. $\square$

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