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 ?tale 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.
Cohomology and torsion cycles over the maximal cyclotomic extension
Rossler D.Co-primo
;Szamuely T.Co-primo
2019-01-01
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 ?tale 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.