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7 - Threefold divisorial contractions to singularities of cE type

Published online by Cambridge University Press:  05 January 2015

J. A. Chen
Affiliation:
National Taiwan University
Christopher D. Hacon
Affiliation:
University of Utah
Mircea Mustaţă
Affiliation:
University of Michigan, Ann Arbor
Mihnea Popa
Affiliation:
University of Illinois, Chicago
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Summary

Abstract

We survey some recent progress in the classification of three-dimensional divisorial contractions to cE points. In particular, we introduce a new structure of three-dimensional cE singularity and use this structure to explain the work of Hayakawa. We also provide some new examples.

Dedicated to Rob Lazarsfeld on the occasion of his sixtieth birthday

1 Introduction

The minimal model program has been one of the main tools in the study of birational algebraic geometry. After some recent advances in the study of the geometry of complex 3-folds, one might hope to build up an explicit classification theory for 3-folds similar to the theory of surfaces by using the minimal model program.

In the minimal model program, divisorial contractions, flips, and flops are considered to be elementary maps. Any birational map obtained from the minimal model program consists of a combination of the above-mentioned maps. Let us briefly recall some known results about three-dimensional birational maps. First of all, Mori and then Cutkosky classified birational maps from nonsingular 3-folds and Gorenstein 3-folds respectively [4, 20]. Tziolas has produced a series of work on divisorial contractions to curves passing through Gorenstein singularities (cf. [23-25]). The recent project of Mori and Prokhorov (cf. [21, 22]) on extremal contractions provides a treatment which is valid for divisorial contractions to curves and for conic bundles. They classified completely divisorial contractions to curves of type IA, IC, and IIB. Flops are studied in Kollár's article [16]. Flips are still quite mysterious, except for some examples in [2, 18].

Divisorial contractions to points are probably the best understood, due mainly to the works of Kawamata, Hayakawa, Markushevich, and Kawakita (cf. [5-7, 10-15, 19]). Divisorial contractions to points of index > 1 are now completely classified and realized as weighted blow-ups. Therefore, it remains to consider contractions to points of index 1, i.e., terminal Gorenstein singularities. The description of contractions to index 1 points can be found in [13]. In fact, contractions to cA points are classified completely in [13]. Recently, Hayakawa started a project to classify contractions to cD and cE points [8, 9].

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Recent Advances in Algebraic Geometry
A Volume in Honor of Rob Lazarsfeld’s 60th Birthday
, pp. 102 - 122
Publisher: Cambridge University Press
Print publication year: 2015

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References

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