English

Boundedness of Fano type fibrations

Algebraic Geometry 2022-09-20 v1

Abstract

In this paper, we prove various results on boundedness and singularities of Fano fibrations and of Fano type fibrations. A Fano fibration is a projective morphism XZX\to Z of algebraic varieties with connected fibres such that XX is Fano over ZZ, that is, XX has "good" singularities and KX-K_X is ample over ZZ. A Fano type fibration is similarly defined where XX is assumed to be close to being Fano over ZZ. This class includes many central ingredients of birational geometry such as Fano varieties, Mori fibre spaces, flipping and divisorial contractions, crepant models, germs of singularities, etc. We develop the theory in the more general framework of log Calabi-Yau fibrations. Dans cet article, nous prouvons divers r\'esultats sur les limites et les singularit\'es de fibrations de Fano et les fibrations de type Fano. Une fibration de Fano est un morphisme projectif XZX\to Z de vari\'et\'es alg\'ebriques \`a fibres connexes tel que XX est Fano sur ZZ, c'est-\`a-dire que XX a de "bonnes" singularit\'es et KX-K_X est ample sur ZZ. Une fibration de type Fano est d\'efinie de fa\c{c}on similaire quand XX est suppos\'e \^etre proche d'\^etre Fano sur ZZ. Cette classe comprend de nombreux ingr\'edients centraux de g\'eom\'etrie birationnelle tels que les vari\'et\'es de fano, les espaces de fibres Mori, le flip et les contractions divisorielles, les mod\`eles r\'ep\'etiteurs, les germes de singularit\'es, etc. Nous d\'eveloppons la th\'eorie dans le cadre plus g\'en\'eral des log-fibrations de Calabi-Yau.

Keywords

Cite

@article{arxiv.2209.08797,
  title  = {Boundedness of Fano type fibrations},
  author = {Caucher Birkar},
  journal= {arXiv preprint arXiv:2209.08797},
  year   = {2022}
}

Comments

To appear in Ann. Sci. ENS, 48 pages; this paper consists of the results of arXiv:1811.10709 on Fano type fibrations; the latter is kept because it contains other results and there are many references to it