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Explicit open images for elliptic curves over $\mathbb{Q}$

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arxiv 2206.14959 v2 pith:E4UFGB4U submitted 2022-06-30 math.NT

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keywords mathbbwidehatcurvesellipticmodularoverlinealgorithmexplicit
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abstract

For a non-CM elliptic curve $E$ defined over $\mathbb{Q}$, the Galois action on its torsion points gives rise to a Galois representation $\rho_E: Gal(\overline{\mathbb{Q}}/\mathbb{Q})\to GL_2(\widehat{\mathbb{Z}})$ that is unique up to isomorphism. A renowned theorem of Serre says that the image of $\rho_E$ is an open, and hence finite index, subgroup of $GL_2(\widehat{\mathbb{Z}})$. We describe an algorithm that computes the image of $\rho_E$ up to conjugacy in $GL_2(\widehat{\mathbb{Z}})$; this algorithm is practical and has been implemented. Up to a positive answer to a uniformity question of Serre and finding all the rational points on a finite number of explicit modular curves of genus at least $2$, we give a complete classification of the groups $\rho_E(Gal(\overline{\mathbb{Q}}/\mathbb{Q}))\cap SL_2(\widehat{\mathbb{Z}})$ and the indices $[GL_2(\widehat{\mathbb{Z}}):\rho_E(Gal(\overline{\mathbb{Q}}/\mathbb{Q}))]$ for non-CM elliptic curves $E/\mathbb{Q}$. Much of the paper is dedicated to the efficient computation of modular curves via modular forms expressed in terms of Eisenstein series.

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Cited by 4 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. Non-split Cartan curves and a characterization of fake elliptic curves

    math.NT 2026-08 conditional novelty 7.0 of 10

    An abelian surface over an imaginary quadratic field has quaternionic multiplication exactly when its residual Galois image is non-split Cartan at two or more primes, under a conjecture that is verified for small levels.

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    math.NT 2025-07 conditional novelty 7.0 of 10

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  3. Effective bounds for adelic Galois representations attached to elliptic curves over the rationals

    math.NT 2024-12 conditional novelty 7.0 of 10

    For every non-CM elliptic curve over Q, the index of the adelic Galois image is bounded by 10^21(h_F(E)+40)^4.42, and by h_F(E)^{3+o(1)} as the height grows.

  4. A uniform bound on the smallest surjective prime of an elliptic curve

    math.NT 2025-01 conditional novelty 6.0 of 10

    For every non-CM elliptic curve over Q, one of its 2-, 3-, or 5-adic Galois representations is surjective unless its j-invariant is one of six listed values, in which case 7 is the minimal surjective prime.

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