The generalized Jacobian reconstruction conjecture for pointed curves

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Let (C,[M])(C,[M]) and (C′,[M′])(C',[M']) be smooth, projective, irreducible pointed curves over Fq{\mathbb F}_q, with moduli m,m′{\mathfrak m},{\mathfrak m}' on C,C′C,C' respectively. Suppose the generalized Jacobians JmJ_{{\mathfrak m}} and Jm′′J_{{\mathfrak m}'}' have dimension at least two. Let UU and U′U' be the complements of the supports of m{\mathfrak m} and m′{\mathfrak m}' in CC and C′C', respectively. If

ψ:Jm(F‾q)→Jm′′(F‾q)\psi:J_{{\mathfrak m}}(\overline{{\mathbb F}}_q)\to J_{{\mathfrak m}'}'(\overline{{\mathbb F}}_q)

is a group isomorphism satisfying ψ(U(F‾q))=U′(F‾q)\psi(U(\overline{{\mathbb F}}_q))=U'(\overline{{\mathbb F}}_q) with respect to the Abel–Jacobi embeddings determined by MM and M′M', then ψ\psi arises from a morphism of curves composed with a limit of Frobenius maps sending m{\mathfrak m} to m′{\mathfrak m}'. The generalized Jacobian reconstruction conjecture. More precisely, there exists an integer mm, an isomorphism

α:Frob⁡m(C)≃C′,\alpha:\operatorname{Frob}^m(C)\simeq C',

and a generalized Frobenius β:F‾q→F‾q\beta:\overline{{\mathbb F}}_q\to\overline{{\mathbb F}}_q restricting to Frob⁡−m\operatorname{Frob}^{-m} on Fq{\mathbb F}_q, such that α∘β:C→C′\alpha\circ\beta:C\to C' sends m{\mathfrak m} to m′{\mathfrak m}' and MM to M′M', and induces ψ\psi on generalized Jacobians. This strengthens the known zero-modulus reconstruction result to generalized Jacobians with moduli.

References

Primary source

Jeremy Booher and José Felipe Voloch, “Recovering affine curves over finite fields from L-functions”, arXiv:2012.08683 (2021).

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