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Lemma 14.3.2D570CDA4FA55

Lemma 14.3.2.D570CDA4FA55 Suppose $u$ is smooth, $\eta =\omega +\mathrm{dd}^{\mathrm{c}}u>0$, and $\eta ^ n\leq \Lambda \omega ^ n$ for a fixed $\Lambda >0$. There are constants $p_0\geq 1$ and $C$ depending only on $\omega $ and $\Lambda $ such that

\[ \int _ X\mathrm{d}(\mathrm{e}^{-pu/2})\wedge \mathrm d^{\mathrm c}(\mathrm{e}^{-pu/2})\wedge \omega ^{n-1} \leq Cp\int _ X\mathrm{e}^{-pu}\omega ^ n\quad (p\geq p_0). \]

Proof. For a fixed real $p\geq 1$, define $M_ k$ for $0\leq k\leq n$ and $J_ k$ for $0\leq k\leq n-1$ by

\[ M_ k=\int _ X\mathrm{e}^{-pu}\eta ^ k\wedge \omega ^{n-k},\qquad J_ k=\int _ X\mathrm{e}^{-pu}\mathrm{d}u\wedge \mathrm d^{\mathrm c}u\wedge \eta ^ k\wedge \omega ^{n-k-1}, \quad J=\sum _{k=0}^{n-1}J_ k. \]

All these numbers are nonnegative. The proof first bounds $pJ$ in terms of the masses $M_ k$, and then bounds these masses by a recurrence. Let $T=\sum _{k=0}^{n-1}\eta ^ k\wedge \omega ^{n-k-1}$, so that $\eta ^ n-\omega ^ n=\mathrm{dd}^{\mathrm{c}}u\wedge T$. Since $\mathrm{d}\eta =\mathrm{d}\omega $, differentiation gives

\[ \mathrm{d}T=n\sum _{k=0}^{n-2}\eta ^ k\wedge \omega ^{n-k-2}\wedge \mathrm{d}\omega . \]

The sum is empty when $n=1$. Stokes' theorem gives the exact identity

\[ \begin{split} \int _ X\mathrm{e}^{-pu}(\eta ^ n-\omega ^ n) & =\int _ X\mathrm{e}^{-pu}\mathrm{dd}^{\mathrm{c}}u\wedge T\\ & =pJ+\int _ X\mathrm{e}^{-pu}\mathrm d^{\mathrm c}u\wedge \mathrm{d}T. \end{split} \]

The density assumption bounds the left-hand side above by $(\Lambda +1)M_0$. Apply lemma 14.3.1 to the last integral, with $\delta =K/p$ for a sufficiently large fixed $K$. The contribution proportional to $J/\delta $ is then at most $pJ/2$, and after absorbing it we obtain

B38AB5EB6BF0 14.3.3
\begin{equation} pJ\leq CM_0+\frac Cp\sum _{k=0}^{n-2}M_ k. \end{equation}

This estimate alone does not suffice, because the mixed weighted masses on the right have not yet been bounded.

For $1\leq k\leq n-2$, a second integration by parts gives

2D25F9B7C178 14.3.4
\begin{equation} M_ k-M_{k-1}=pJ_{k-1}+R_ k, \qquad R_ k=\int _ X\mathrm{e}^{-pu}\mathrm d^{\mathrm c}u\wedge \mathrm{d}(\eta ^{k-1}\wedge \omega ^{n-k}). \end{equation}

The derivative in $R_ k$ has two terms, with coefficients $k-1$ and $n-k$. Applying the pointwise estimate with $\delta =1/p$ to each of them, and omitting terms with negative indices, we obtain

\[ |R_ k|\leq Cp(J_{k-2}+J_{k-1}) +\frac Cp(M_{k-2}+M_{k-1}), \qquad M_{-1}=J_{-1}=0. \]

Consequently, for $p\geq 1$,

\[ M_ k\leq C(M_{k-1}+M_{k-2}+pJ). \]

Induction over the finitely many values of $k$ proves

\[ \sum _{k=0}^{n-2}M_ k\leq C(M_0+pJ). \]

For $n=2$ this is immediate, and for $n=1$ the sum is empty. Inserting this bound in (14.3.3) gives $pJ\leq CM_0+C'J$. For $p\geq 2C'$ the last term can be absorbed, and $pJ\leq CM_0$.

Finally,

\[ \int _ X\mathrm{d}(\mathrm{e}^{-pu/2})\wedge \mathrm d^{\mathrm c}(\mathrm{e}^{-pu/2})\wedge \omega ^{n-1} =\frac{p^2}{4}J_0\leq \frac{p^2}{4}J\leq CpM_0. \]

This proves the claimed estimate for all $p\geq p_0$. $\square$

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