Compositio Mathematica

Research Article

Hilbert’s 14th problem over finite fields and a conjecture on the cone of curves

Burt Totaroa1

a1 DPMMS, Wilberforce Road, Cambridge CB3 0WB, UK (email: b.totaro@dpmms.cam.ac.uk)

Abstract

We give the first examples over finite fields of rings of invariants that are not finitely generated. (The examples work over arbitrary fields, for example the rational numbers.) The group involved can be as small as three copies of the additive group. The failure of finite generation comes from certain elliptic fibrations or abelian surface fibrations having positive Mordell–Weil rank. Our work suggests a generalization of the Morrison–Kawamata cone conjecture on Calabi–Yau fiber spaces to klt Calabi–Yau pairs. We prove the conjecture in dimension two under the assumption that the anticanonical bundle is semi-ample.

(Received September 25 2007)

(Accepted February 19 2008)

2000 Mathematics subject classification

  • 13A50;
  • 14E30;
  • 14J32

Keywords

  • finite generation;
  • ring of invariants;
  • elliptic fibration;
  • Calabi–Yau fiber space;
  • klt pair;
  • cone conjecture