Zywina's agreeable-closure classification for rational non-CM jj-invariants

Let j\Qj \in \Q be a non-CM rational jj-invariant. Write \cGj\cG_j for the associated adelic Galois-image subgroup, let (\cGj)agr(\cG_j)_{\operatorname{agr}} be its agreeable closure, and let X(\cGj)agrX_{(\cG_j)_{\operatorname{agr}}} be the corresponding modular curve. Zywina's agreeable-closure classification. If the modular curve X(\cGj)agrX_{(\cG_j)_{\operatorname{agr}}} has infinitely many rational points, then the intersection \cGjSL(Z^)\cG_j \cap \operatorname{SL}(\widehat{\mathbb Z}) is one of the conjugacy classes given in the paper's table of infinite special-linear intersections. On the other hand, if X(\cGj)agrX_{(\cG_j)_{\operatorname{agr}}} has finitely many rational points, then jj and \cGj\cG_j are given in the paper's table of exceptional jj-invariants. This is a conjectural classification of the possible agreeable closures, and hence of the intersections with SL(Z^)\operatorname{SL}(\widehat{\mathbb Z}), for non-CM elliptic curves over Q\mathbb Q; the stated alternatives organize the cases according to whether the associated modular curve has infinitely or finitely many rational points.

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Primary source

Kenji Terao, “Degrees of points with rational j-invariant on X_0(n) and X_1(n)”, arXiv:2507.13199 (2025).

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