# A $p$-adic Analytic Approach to the Absolute Grothendieck Conjecture

### Takahiro Murotani

Kyoto University, Japan

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## Abstract

Let $K$ be a field, $G_K$ the absolute Galois group of $K$, $X$ a hyperbolic curve over $K$ and $\pi_1(X)$ the \'{e}tale fundamental group of $X$. The absolute Grothendieck conjecture in anabelian geometry asks the following question: Is it possible to recover $X$ group-theoretically, solely from $\pi_1(X)$ (not $\pi_1(X)\twoheadrightarrow G_K$)? When $K$ is a $p$-adic field (i.e., a finite extension of $\mathbb{Q}_p$), this conjecture (called the $p$-adic absolute Grothendieck conjecture) is unsolved. To approach this problem, we introduce a certain $p$-adic analytic invariant defined by Serre (which we call $i$-invariant). Then the absolute $p$-adic Grothendieck conjecture can be reduced to the following problems: (A) determining whether a proper hyperbolic curve admits a rational point from the data of the $i$-invariants of the sets of rational points of the curve and its coverings; (B) recovering the $i$-invariant of the set of rational points of a proper hyperbolic curve group-theoretically. The main results of the present paper give a complete affirmative answer to (A) and a partial affirmative answer to (B).

## Cite this article

Takahiro Murotani, A $p$-adic Analytic Approach to the Absolute Grothendieck Conjecture. Publ. Res. Inst. Math. Sci. 55 (2019), no. 2, pp. 401–451

DOI 10.4171/PRIMS/55-2-6