Geyer–Jarden's torsion conjecture for abelian varieties

Let KK be a finitely generated field over its prime field, let ee be a positive integer, and let σ\sigma range over Gal(Ksep/K)e\mathrm{Gal}(K^\mathrm{sep}/K)^e. For almost all such σ\sigma, let AA be an abelian variety of positive dimension defined over K~(σ)\tilde{K}(\sigma), with Ator(K~(σ))A_\mathrm{tor}(\tilde{K}(\sigma)) denoting its torsion subgroup and A(K~(σ))[n]A(\tilde{K}(\sigma))[n] its group of nn-torsion points. Geyer–Jarden's conjecture. Theorem 1.2 remains true when the elliptic curve EE is replaced by an arbitrary abelian variety AA of positive dimension: if e=1e=1, then Ator(K~(σ))A_\mathrm{tor}(\tilde{K}(\sigma)) is infinite, and there exist infinitely many primes ll such that A(K~(σ))[l]0A(\tilde{K}(\sigma))[l]\neq 0; if e2e\geq 2, then Ator(K~(σ))A_\mathrm{tor}(\tilde{K}(\sigma)) is finite; and if e1e\geq 1, then for every prime ll, the group A(K~(σ))[l]=i=1A(K~(σ))[li]A(\tilde{K}(\sigma))[l^\infty]=\bigcup_{i=1}^\infty A(\tilde{K}(\sigma))[l^i] is finite. The conjecture generalizes Geyer and Jarden's theorem on torsion subgroups of elliptic curves. Jacobson and Jarden proved that it is true when KK is a finite field; its general status is therefore not fully resolved in the source.

Sources & referencesView supporting material

Primary source

Takuya Asayama, “Torsion points of Drinfeld modules over large algebraic extensions of finitely generated function fields”, arXiv:2007.13949 (2020).

Additional references

2 papers in this index state this conjecture (2010–2020). The statement above is taken from the most recent of them; the others are arXiv:1010.2444.

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