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arXiv · 2212.13327

CM Elliptic Curves: Volcanoes, Reality and Applications, Part II

Pete L. Clark·Frederick Saia
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Abstract

Let $M \mid N$ be positive integers, and let $\Delta$ be the discriminant of an order in an imaginary quadratic field $K$. When $\Delta_K < -4$, the first author determined the fiber of the morphism $X_0(M,N) \rightarrow X(1)$ over the closed point $J_{\Delta}$ corresponding to $\Delta$ and showed that all fibers of the map $X_1(M,N) \rightarrow X_0(M,N)$ over $J_{\Delta}$ were connected. Here we complement this prior work by addressing the most difficult cases $\Delta_K \in \{-3,-4\}$. These works provide all the information needed to compute, for each positive integer $d$, all subgroups of $E(F)[\operatorname{tors}]$, where $F$ is a number field of degree $d$ and $E_{/F}$ is an elliptic curve with complex multiplication.

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Pete L. Clark, Frederick Saia. 2022-12-27. CM Elliptic Curves: Volcanoes, Reality and Applications, Part II. https://arxiv.org/abs/2212.13327

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