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Cohomology and torsion cycles over the maximal cyclotomic extension

  • Damian Rössler EMAIL logo and Tamás Szamuely

Abstract

A classical theorem by K. Ribet asserts that an abelian variety defined over the maximal cyclotomic extension K of a number field has only finitely many torsion points. We show that this statement can be viewed as a particular case of a much more general one, namely that the absolute Galois group of K acts with finitely many fixed points on the étale cohomology with 𝐐/𝐙-coefficients of a smooth proper K¯-variety defined over K. We also present a conjectural generalization of Ribet’s theorem to torsion cycles of higher codimension. We offer supporting evidence for the conjecture in codimension 2, as well as an analogue in positive characteristic.

Funding statement: The second author was partially supported by NKFI grant No. K112735.

Acknowledgements

Many thanks to Anna Cadoret, Jean-Louis Colliot-Thélène, Wayne Raskind and Douglas Ulmer. We are also very grateful to the referee for his insightful comments which in particular enabled us to remove an unnecessary restriction in the statement of Theorem 1.9.

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Received: 2016-05-31
Revised: 2016-10-26
Published Online: 2017-01-12
Published in Print: 2019-07-01

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