The generalized Jacobian reconstruction conjecture for pointed curves

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,CC,C' respectively. Suppose the generalized Jacobians JmJ_{{\mathfrak m}} and JmJ_{{\mathfrak m}'}' have dimension at least two. Let UU and UU' be the complements of the supports of m{\mathfrak m} and m{\mathfrak m}' in CC and CC', respectively. If

ψ:Jm(Fq)Jm(Fq)\psi:J_{{\mathfrak m}}(\overline{{\mathbb F}}_q)\to J_{{\mathfrak m}'}'(\overline{{\mathbb F}}_q)

is a group isomorphism satisfying ψ(U(Fq))=U(Fq)\psi(U(\overline{{\mathbb F}}_q))=U'(\overline{{\mathbb F}}_q) with respect to the Abel–Jacobi embeddings determined by MM and MM', 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:Frobm(C)C,\alpha:\operatorname{Frob}^m(C)\simeq C',

and a generalized Frobenius β:FqFq\beta:\overline{{\mathbb F}}_q\to\overline{{\mathbb F}}_q restricting to Frobm\operatorname{Frob}^{-m} on Fq{\mathbb F}_q, such that αβ:CC\alpha\circ\beta:C\to C' sends m{\mathfrak m} to m{\mathfrak m}' and MM to MM', and induces ψ\psi on generalized Jacobians. This strengthens the known zero-modulus reconstruction result to generalized Jacobians with moduli.

Sources & referencesView supporting material

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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