On the descending central sequence of absolute Galois groups

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Efrat, Ido
Minac, Jan
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Abstract
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Let $p$ be an odd prime number and $F$ a field containing a primitive $p$th root of unity. We prove a new restriction on the group-theoretic structure of the absolute Galois group $G_F$ of $F$. Namely, the third subgroup $G_F^{(3)}$ in the descending $p$-central sequence of $G_F$ is the intersection of all open normal subgroups $N$ such that $G_F/N$ is 1, $\mathbb{Z}/p^2$, or the modular group $M_{p^3}$ of order $p^3$.
Comment: We implemented the referee's comments. The paper will appear in The American Journal of Mathematics
Keywords
Mathematics - Number Theory, Mathematics - K-Theory and Homology, 12F10, 12G05, 12E30
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