An elliptic curve $E$ defined over a number field $K$ is a $\mathbb{Q}$**-curve** if it is isogenous over $\overline{K}$ to each of its Galois conjugates. Note that the isogenies need not be defined over $K$ itself.

An elliptic curve which is the base change of a curve defined over $\mathbb{Q}$ is a $\mathbb{Q}$-curve, but not all $\mathbb{Q}$-curves are base-change curves.

Elliptic curves with CM are all $\mathbb{Q}$-curves, as are all those whose $j$-invariant is in $\mathbb{Q}$.

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- Last edited by John Jones on 2018-06-19 01:05:06

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- 2018-06-19 01:05:06 by John Jones (Reviewed)