The good-reduction lifting conjecture for cyclic covers of the projective line

Let KK be the ground field, let X=PK1X=\mathbb{P}^1_K, and let xˉ0\bar{x}_0 be the distinguished branch point with residue field κ0\kappa_0. For a character χHpn1(K)\chi\in H^1_{p^n}(\mathbb{K}), call it admissible if it defines the relevant Z/pn\mathbb{Z}/p^n-cover, and call it a lift of χˉHpn1(κ0)\bar{\chi}\in H^1_{p^n}(\kappa_0) when its reduction is χˉ\bar{\chi}. Say that such a character has good reduction when it has étale reduction and the cover corresponding to its reduction is smooth.

Suppose that X=PK1X=\mathbb{P}^1_K. Let χˉHpn1(κ0)\bar{\chi}\in H^1_{p^n}(\kappa_0) be a character of order pnp^n, unramified outside xˉ0\bar{x}_0. Then, after replacing KK by a finite extension if necessary, there exists an admissible character χHpn1(K)\chi\in H^1_{p^n}(\mathbb{K}) with good reduction lifting χˉ\bar{\chi}.

This is a reformulation of the local Oort conjecture for Z/pn\mathbb{Z}/p^n-covers of the projective line. Its status depends on the local lifting result being used; the supplied text gives no resolution evidence for this formulation.

Sources & referencesView supporting material

Primary source

Andrew Obus and Stefan Wewers, “Cyclic Extensions and the Local Lifting Problem”, arXiv:1203.5057 (2012).

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