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arXiv · 2212.12635

CM points on Shimura curves via QM-equivariant isogeny volcanoes

Frederick Saia
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Abstract

We study CM points on the Shimura curves $X_0^D(N)_{/\mathbb{Q}}$ and $X_1^D(N)_{/\mathbb{Q}}$, parametrizing abelian surfaces with quaternionic multiplication and extra level structure. A description of the locus of points with CM by a specified order is obtained for general level, via an isogeny-volcano approach in analogy to work of Clark and Clark--Saia in the $D=1$ case of modular curves. This allows for a count of all points with CM by a specified order on such a curve, and a determination of all primitive residue fields and primitive degrees of such points on $X_0^D(N)_{/\mathbb{Q}}$. We leverage computations of least degrees towards the existence of sporadic CM points on $X_0^D(N)_{/\mathbb{Q}}$.

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Frederick Saia. 2022-12-24. CM points on Shimura curves via QM-equivariant isogeny volcanoes. https://doi.org/10.2140/pjm.2024.332.321

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