English

On the birational section conjecture with local conditions

Algebraic Geometry 2015-09-18 v3 Group Theory Number Theory

Abstract

A birationally liftable Galois section s of a hyperbolic curve X/k over a number field k yields an adelic point x(s) in the smooth completion of X. We show that x(s) is X-integral outside a set of places of Dirichlet density 0, or s is cuspidal. The proof relies on GL2(F)GL_2(F_\ell)-quotients of π1(U)\pi_1(U) for some open U of X. If k is totally real or imaginary quadratic, we prove that all birationally adelic, non-cuspidal Galois sections come from rational points as predicted by the section conjecture of anabelian geometry. As an aside we also obtain a strong approximation result for rational points on hyperbolic curves over Q or imaginary quadratic fields.

Keywords

Cite

@article{arxiv.1203.3236,
  title  = {On the birational section conjecture with local conditions},
  author = {Jakob Stix},
  journal= {arXiv preprint arXiv:1203.3236},
  year   = {2015}
}

Comments

Theorem C (and Section 7) of the original version have been deleted due to a gap in the proof. This is the journal version

R2 v1 2026-06-21T20:34:13.808Z