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Singularities on the base of a Fano type fibration

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Veröffentlicht/Copyright: 16. Mai 2014

Abstract

Let f:XZ be a Mori fibre space. McKernan conjectured that the singularities of Z are bounded in terms of the singularities of X. Shokurov independently proposed a more general conjecture in the setting of pairs: let (X,B) be a pair with klt singularities and f:XZ be a contraction such that KX+B0/Z and that the general fibres of f are Fano type varieties; adjunction for fibre spaces produces a discriminant divisor BZ and a moduli divisor MZ on Z. It is then conjectured that the singularities of (Z,BZ+MZ) are bounded in terms of the singularities of (X,B). We prove Shokurov's conjecture when (F,SuppBF) belongs to a bounded family where F is a general fibre of f and KF+BF=(KX+B)|F.

Thanks to Yuri Prokhorov for useful discussions on his results with Mori. Thanks to Florin Ambro and Vyacheslav V. Shokurov for their historical comments. Also thanks to the referee for valuable corrections and suggestions.

Received: 2013-5-9
Revised: 2014-3-16
Published Online: 2014-5-16
Published in Print: 2016-6-1

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