Anabelian Intersection Theory I: The Conjecture of Bogomolov-Pop and Applications

TL;DR

This paper proves a conjecture linking isomorphisms of certain function fields to outer automorphisms of their Galois groups, establishing anabelian properties for higher-dimensional varieties over algebraic closures of prime fields.

Contribution

It completes the proof of the Bogomolov-Pop conjecture, showing a bijection between field isomorphisms and Galois group automorphisms for fields of transcendence degree at least 2.

Findings

Function fields of dimension ≥ 2 are anabelian.

Established a bijection between field isomorphisms and Galois automorphisms.

Provided criteria for elements of the Grothendieck-Teichmüller group to lie in the absolute Galois group.

Abstract

We finish the proof of the conjecture of F. Bogomolov and F. Pop: Let $F_{1}$ and $F_{2}$ be fields finitely-generated and of transcendence degree $\geq 2$ over $k_{1}$ and $k_{2}$, respectively, where $k_{1}$ is either $\bar{\mathbb{Q}}$ or $\bar{\mathbb{F}}_{p}$, and $k_{2}$ is algebraically closed. We denote by $G_{F_1}$ and $G_{F_2}$ their respective absolute Galois groups. Then the canonical map $\varphi_{F_{1}, F_{2}}: \Isom^i(F_1, F_2)\rightarrow \Isom^{\Out}_{\cont}(G_{F_2}, G_{F_1})$ from the isomorphisms, up to Frobenius twists, of the inseparable closures of $F_1$ and $F_2$ to continuous outer isomorphisms of their Galois groups is a bijection. Thus, function fields of varieties of dimension $\geq 2$ over algebraic closures of prime fields are anabelian. We apply this to give a necessary and sufficient condition for an element of the Grothendieck-Teichm\"uller group to be an element of the absolute Galois group of $\bar{\mathbb{Q}}$.