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Pré-Publication, Document De Travail Année : 2020

QUASI-POSITIVE ORBIFOLD COTANGENT BUNDLES ; PUSHING FURTHER AN EXAMPLE BY JUNJIRO NOGUCHI

Résumé

In this work, we investigate the positivity of logarithmic and orbifold cotangent bundles along hyperplane arrangements in projective spaces. We show that a very interesting example given by Noguchi (as early as in 1986) can be pushed further to a very great extent. Key ingredients of our approach are the use of Fermat covers and the production of explicit global symmetric differentials. This allows us to obtain some new results in the vein of several classical results of the literature on hyperplane arrangements. These seem very natural using the modern point of view of augmented base loci, and working in Campana's orbifold category. As an application of our results, we derive two new orbifold hyperbolicity results, going beyond some classical results of value distribution theory. 0. Introduction Positive and quasi-positive cotangent bundles.-In recent years, families of varieties with ample cotangent bundles have attracted a lot of attention (see e.g. [Deb05, Xie18, BD18a, Den20, Moh18, CR20, Ete19]), and there have been significant progress in this area (even though finding an explicit surface with ample cotangent bundle in P 4 is still a tremendous challenge). With the development of our understanding, the enriching of techniques, and in connection with hyperbolicity problems, some variations of this problem have started to emerge. For instance, in [BD18b], the authors have been interested in the determination of the augmented base locus of logarithmic cotangent bundles along normal crossing divisors in projective spaces. The stable base locus B(L) ⊆ X of a line bundle L on a projective variety X is defined as the intersection of the base loci of all multiples of L. Then, the augmented base locus (or non-ample locus) B + (L) ⊆ X is B + (L) q∈N B(qL − A), for any ample line bundle A → X. The augmented base locus of a line bundle is a geometric measure of the positivity of its sheaf of global sections. In particular, it is different from the base variety when the line bundle is big, and it is empty when the line bundle is ample. For vector bundles, one studies the augmented base locus of the Serre line bundle on their projectivizations. The idea of augmented base loci for vector bundles can be traced back to [Nog77], where it was already used in connection to hyperbolicity (see below).
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Dates et versions

hal-02896877 , version 1 (10-07-2020)
hal-02896877 , version 2 (18-07-2022)
hal-02896877 , version 3 (19-09-2023)
hal-02896877 , version 4 (29-03-2024)

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  • HAL Id : hal-02896877 , version 1

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Lionel Darondeau, Erwan Rousseau. QUASI-POSITIVE ORBIFOLD COTANGENT BUNDLES ; PUSHING FURTHER AN EXAMPLE BY JUNJIRO NOGUCHI. 2020. ⟨hal-02896877v1⟩
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