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arXiv · 2307.14131

On $r$-isogenies over $\mathbb{Q}(\zeta_r)$ of elliptic curves with rational $j$-invariants

Filip Najman
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Abstract

The main goal of this paper is to determine for which prime numbers $r\geq 3$ can an elliptic curve~$E$ defined over $\mathbb Q$ have an $r$-isogeny over $\mathbb Q(\zeta_r)$. We study this question under various assumptions on the 2-torsion of $E$. Apart from being a natural question itself, the mod~$r$ representations attached to such $E$ arise in the Darmon program for the generalized Fermat equation of signature $(r,r,p)$, playing a key role in the proof of modularity of certain Frey varieties in the recent work of Billerey, Chen, Dieulefait and Freitas.

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Filip Najman. 2023-07-26. On $r$-isogenies over $\mathbb{Q}(\zeta_r)$ of elliptic curves with rational $j$-invariants. https://arxiv.org/abs/2307.14131

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