Splitting conjecture for the wild inertia extension of a local field

About 21 years old · traced to

Let K=QqK=\mathbb{Q}_q be unramified over Qp\mathbb{Q}_p, with maximal unramified extension KnrK^\mathrm{nr} and separable algebraic closure KsK^s. Let P=Gal⁡(Ks/Ktr)P=\operatorname{Gal}(K^s/K^\mathrm{tr}) be the wild inertia subgroup, and identify the tame quotient with Z^(1)(¬p)\widehat{\mathbb{Z}}(1)(\neg p). Splitting conjecture. The extension

1→P→Gal⁡(Ks/Knr)→Z^(1)(¬p)→11\to P\to \operatorname{Gal}(K^s/K^\mathrm{nr})\to \widehat{\mathbb{Z}}(1)(\neg p)\to 1

splits, so that

Gal⁡(Ks/Knr)≅P⋊Z^(1)(¬p).\operatorname{Gal}(K^s/K^\mathrm{nr})\cong P\rtimes\widehat{\mathbb{Z}}(1)(\neg p).

The claim describes the inertia group as a semidirect product of its pro-pp wild part and its prime-to-pp tame quotient. The source notes that the splitting would be immediate for finite kernel or quotient, but does not state a resolution in the general profinite case.

References

Primary source

Jack Morava, “Toward a fundamental groupoid for the stable homotopy category”, arXiv:math/0509001 (2009).

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