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

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 $\ge 2$ 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 $φ_{F_{1}, F_{2}}: \Isom^i(F_1, F_2)\rightarrow \Isom^{\Out}_{\cont}(G_{F_2}, G_{F_1})$ 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 $\ge 2$ over algebraic closures of prime fields are anabelian. We apply this to give a necessary and sufficient condition for an element of the Grothendieck-Teichmüller group to be an element of the absolute Galois group of $\bar{\mathbb{Q}}$.

30 pages, comments welcome!