Some remarks on almost rational torsion points
Author(s) -
John Boxall,
David Grant
Publication year - 2006
Publication title -
journal de théorie des nombres de bordeaux
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.663
H-Index - 26
eISSN - 2118-8572
pISSN - 1246-7405
DOI - 10.5802/jtnb.531
Subject(s) - mathematics , elliptic curve , abelian variety , abelian group , complex multiplication , torsion (gastropod) , finite field , algebraic number field , commutative property , torsion subgroup , complex torus , discrete mathematics , pure mathematics , elementary abelian group , arithmetic of abelian varieties , algebraic number , combinatorics , rank of an abelian group , torus , mathematical analysis , geometry , medicine , surgery
For a commutative algebraic group G over a perfect field k, Ribet defined the set of almost rational torsion points G ar,k of G over k. For positive integers d, g, we show there is an integer Ud,g such that for all tori T of dimension at most d over number fields of degree at most g, T ar tors,k T(Ud,g). We show the corresponding result for abelian varieties with complex multi- plication, and under an additional hypothesis, for elliptic curves without complex multiplication. Finally, we show that except for an explicit finite set of semi-abelian varieties G over a finite field k, G ar,k is infinite, and use this to show for any abelian variety A over a p-adic field k, there is a finite extension of k over which A ar,k is infinite.
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