Geyer–Jarden's torsion conjecture for abelian varieties

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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 e≥2e\geq 2, then Ator(K~(σ))A_\mathrm{tor}(\tilde{K}(\sigma)) is finite; and if e≥1e\geq 1, then for every prime ll, the group A(K~(σ))[l∞]=⋃i=1∞A(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.

References

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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