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arXiv · 1502.01288

Local-Global principles for certain images of Galois representations

Anastassia Etropolski
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Abstract

Let $K$ be a number field and let $E/K$ be an elliptic curve whose mod $\ell$ Galois representation locally has image contained in a group $G$, up to conjugacy. We classify the possible images for the global Galois representation in the case where $G$ is a Cartan subgroup or the normalizer of a Cartan subgroup. When $K = \mathbf{Q}$, we deduce a counterexample to the local-global principle in the case where $G$ is the normalizer of a split Cartan and $\ell = 13$. In particular, there are at least three elliptic curves (up to twist) over $\mathbf{Q}$ whose mod $13$ image of Galois is locally contained in the normalizer of a split Cartan, but whose global image is not.

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Anastassia Etropolski. 2015-02-04. Local-Global principles for certain images of Galois representations. https://arxiv.org/abs/1502.01288

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