Pome

Proposition 12.21.458574FAEC5B7

Proposition 12.21.4.58574FAEC5B7 For each integer $m>1$ there is a smooth semipositive nonclosed form on $X$ with common order $1-1/m$. For each $b>0$ there is also one with

\[ \mathcal V_\mu (\theta +\epsilon h)\sim \frac{2b}{\pi \log (1/\epsilon )} \quad (\epsilon \downarrow 0); \]

it has volume zero and both orders zero.

Proof. In proposition 12.21.1 take $a=b>0$ and $r=0$. Fix a point $z_0\in E$ and a flat coordinate $\zeta =z-z_0$ on a small disk about $z_0$. Choose $q$ smooth, positive outside $z_0$, and equal to $|\zeta |^{2m}$ on that disk; a positive smooth extension exists away from the disk. For $m=1$, polar coordinates give

\[ I=\int _ E\frac{\omega _1}{q+\epsilon } =\pi \log (1/\epsilon )+O(1), \]

and (12.21.2) gives the asymptotic formula of the statement. If $m>1$, the substitution $s=|\zeta |^2=\epsilon ^{1/m}t$ gives

\[ I\sim C_ m\epsilon ^{1/m-1},\qquad C_ m=\pi \int _0^\infty \frac{\mathrm{d} t}{1+t^ m}>0, \]

so the common order is $1-1/m$. In the logarithmic case, $\lambda _\mu (\theta )\geq 0$ by semipositivity, while $\lambda _\mu (\theta )\leq \lambda _\mu (\theta +\epsilon h)\to 0$ by monotonicity; hence $\mathcal V_\mu (\theta )=0$. Moreover, the quotient of the volume by $\epsilon ^\delta $ diverges for every $\delta >0$, so both orders vanish. Finally, $\mathrm{d}\theta =\mathrm{d} q\wedge \omega _2\ne 0$, so these backgrounds are not closed. $\square$

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