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Let $(M, \omega)$ be a compact Kähler manifold. An $\omega$-quasi-plurisubharmonic function on $M$ is an upper semi-continuous function $\varphi : M \to \mathbb{R} \cup \{ - \infty \}$ such that $\omega + dd^c \varphi \geq 0$ in the sense of currents. The prototype in the non-compact or quasi-projective setting is $\log | f |^2$, where $f$ is a holomorphic function (e.g., the local defining section for a divisor $D \subset M$).

Are there examples of quasi-plurisubharmonic functions with polynomial decay?

Here is a non-example: Suppose we have a smooth divisor $D$ in $M$ with local defining section $s_D$. For $\varepsilon >0$, we may consider $| s_D |^{-2\varepsilon}$, where the norm is taken with respect to a Hermitian metric on the line bundle $\mathscr{O}_D$ associated to $D$. A standard calculation gives $$\sqrt{-1} \partial \overline{\partial} | s_D |^{-2\varepsilon} \geq \varepsilon | s_D |^{-2\varepsilon} R_D,$$ where $R_D$ is the curvature form of the Hermitian metric on $\mathscr{O}_D$. This example blows up at a polynomial rate, but in the wrong direction. I want a quasi-plurisubharmonic function which decays to $-\infty$ polynomially. Of course, this is not quasi-plurisubharmonic either.

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  • $\begingroup$ quasi-psh functions are exponentially integrable (Hörmander "An introduction to complex analysis in several variables" Thm 4.4.5) $\endgroup$
    – YangMills
    Commented Jun 21, 2021 at 4:28
  • $\begingroup$ to be clear, my previous comment shows that there are no quasi-psh functions with "polynomial decay", since those would not be exponentially integrable $\endgroup$
    – YangMills
    Commented Jun 22, 2021 at 19:09

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