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Numerical criteria for divisors on to be ample

Part of: Birational geometry Curves

Published online by Cambridge University Press:  04 September 2009

Angela Gibney
Angela Gibney*
Affiliation:
Department of Mathematics, University of Georgia, Athens, GA 30602, USA (email: [email protected])
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Abstract

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The moduli space of n-pointed stable curves of genus g is stratified by the topological type of the curves being parameterized: the closure of the locus of curves with k nodes has codimension k. The one-dimensional components of this stratification are smooth rational curves called F-curves. These are believed to determine all ample divisors. F-conjecture 

A divisor on  is ample if and only if it positively intersects theF-curves.

In this paper, proving the F-conjecture on is reduced to showing that certain divisors on for N⩽g+n are equivalent to the sum of the canonical divisor plus an effective divisor supported on the boundary. Numerical criteria and an algorithm are given to check whether a divisor is ample. By using a computer program called the Nef Wizard, written by Daniel Krashen, one can verify the conjecture for low genus. This is done on for g⩽24, more than doubling the number of cases for which the conjecture is known to hold and showing that it is true for the first genera such that is known to be of general type.

MSC classification

Secondary: 14H10: Families, moduli (algebraic) 14E30: Minimal model program (Mori theory, extremal rays)
Type
Research Article
Information
Compositio Mathematica , Volume 145 , Issue 5 , September 2009 , pp. 1227 - 1248
Copyright
Copyright © Foundation Compositio Mathematica 2009

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