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Elliptic curves with abelian division fields. (English) Zbl 1410.11051

Summary: Let \(E\) be an elliptic curve over \(\mathbb Q\), and let \(n\geq 1\). The central object of study of this article is the division field \(\mathbb Q(E[n])\) that results by adjoining to \(\mathbb Q\) the coordinates of all \(n\)-torsion points on \(E(\overline{\mathbb Q})\). In particular, we classify all curves \(E/\mathbb Q\) such that \(\mathbb Q(E[n])\) is as small as possible, that is, when \(\mathbb Q(E[n])=\mathbb Q(\zeta _n)\), and we prove that this is only possible for \(n=2,3,4\), or 5. More generally, we classify all curves such that \(\mathbb Q(E[n])\) is contained in a cyclotomic extension of \(\mathbb Q\) or, equivalently (by the Kronecker-Weber theorem), when \(\mathbb Q(E[n])/\mathbb Q\) is an abelian extension. In particular, we prove that this only happens for \(n=2,3,4,5,6\), or 8, and we classify the possible Galois groups that occur for each value of \(n\).

MSC:

11G05 Elliptic curves over global fields
14H52 Elliptic curves

References:

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