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Positivity properties of the bundle of logarithmic tensors on compact Kähler manifolds
Published online by Cambridge University Press: 21 September 2016
Abstract
Let $X$ be a compact Kähler manifold, endowed with an effective reduced divisor
$B=\sum Y_{k}$ having simple normal crossing support. We consider a closed form of
$(1,1)$ -type
$\unicode[STIX]{x1D6FC}$ on
$X$ whose corresponding class
$\{\unicode[STIX]{x1D6FC}\}$ is nef, such that the class
$c_{1}(K_{X}+B)+\{\unicode[STIX]{x1D6FC}\}\in H^{1,1}(X,\mathbb{R})$ is pseudo-effective. A particular case of the first result we establish in this short note states the following. Let
$m$ be a positive integer, and let
$L$ be a line bundle on
$X$ , such that there exists a generically injective morphism
$L\rightarrow \bigotimes ^{m}T_{X}^{\star }\langle B\rangle$ , where we denote by
$T_{X}^{\star }\langle B\rangle$ the logarithmic cotangent bundle associated to the pair
$(X,B)$ . Then for any Kähler class
$\{\unicode[STIX]{x1D714}\}$ on
$X$ , we have the inequality
$$\begin{eqnarray}\displaystyle \int _{X}c_{1}(L)\wedge \{\unicode[STIX]{x1D714}\}^{n-1}\leqslant m\int _{X}(c_{1}(K_{X}+B)+\{\unicode[STIX]{x1D6FC}\})\wedge \{\unicode[STIX]{x1D714}\}^{n-1}.\end{eqnarray}$$
$X$ is projective, then this result gives a generalization of a criterion due to Y. Miyaoka, concerning the generic semi-positivity: under the hypothesis above, let
$Q$ be the quotient of
$\bigotimes ^{m}T_{X}^{\star }\langle B\rangle$ by
$L$ . Then its degree on a generic complete intersection curve
$C\subset X$ is bounded from below by
$$\begin{eqnarray}\displaystyle \biggl(\frac{n^{m}-1}{n-1}-m\biggr)\int _{C}(c_{1}(K_{X}+B)+\{\unicode[STIX]{x1D6FC}\})-\frac{n^{m}-1}{n-1}\int _{C}\unicode[STIX]{x1D6FC}.\end{eqnarray}$$
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- © The Authors 2016
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