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arXiv · 2306.04844

Etale descent obstruction and anabelian geometry of curves over finite fields

Brendan Creutz·Jose Felipe Voloch
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Abstract

Let $C$ and $D$ be smooth, proper and geometrically integral curves over a finite field $F$. Any morphism from $D$ to $C$ induces a morphism of their \'etale fundamental groups. The anabelian philosophy proposed by Grothendieck suggests that, when $C$ has genus at least $2$, all open homomorphisms between the \'etale fundamental groups should arise in this way from a nonconstant morphism of curves. We relate this expectation to the arithmetic of the curve $C_K$ over the global function field $K = F(D)$. Specifically, we show that there is a bijection between the set of conjugacy classes of well-behaved morphism of fundamental groups and locally constant adelic points of $C_K$ that survive \'etale descent. We use this to provide further evidence for the anabelian conjecture by relating it to another recent conjecture by Sutherland and the second author.

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Brendan Creutz, Jose Felipe Voloch. 2023-06-08. Etale descent obstruction and anabelian geometry of curves over finite fields. https://doi.org/10.46298/epiga.2024.11483

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