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An elliptic curve is an algebraic curve of genus one with some additional properties. Questions with this tag will often have the top-level tags nt.number-theory or ag.algebraic-geometry. Note also the tag arithmetic-geometry as well as some related tags such as rational-points, abelian-varieties, heights. Please do not use this tag for questions related to ellipses; instead use conic-sections.

6 votes
Accepted

Image of isogeny of elliptic curves determines kernel?

It is possible. Suppose $E$ has complex multiplication defined over a number field $F$ by the ring of integers $\mathcal{O}_K$ in a quadratic imaginary field $K$ (and we take $K$ that only has $\pm 1$ …
Kestutis Cesnavicius's user avatar
6 votes

Root number of a quadratic twist of an elliptic curve

I will prove a stronger Claim: Let $A$ be a $g$-dimensional abelian variety over $\mathbb{Q}$, let $N_A$ be its conductor, let $D$ be a squarefree integer, let $\psi_D$ be the Dirichlet character ass …
Kestutis Cesnavicius's user avatar
1 vote

Q(\sqrt{-l_0}) satisfies Heegner hypothesis for an Elliptic curve of conductor C implies C i...

It is a general fact that if $K$ is a number field, $K'/K$ is a quadratic extension, $E \rightarrow \mathrm{Spec}\, K$ is an elliptic curve, and $E' \rightarrow \mathrm{Spec}\, K'$ is its quadratic tw …
Kestutis Cesnavicius's user avatar
8 votes
2 answers
1k views

Distance functions on elliptic curves over number fields

My question originates from the book of Silverman "The Aritmetic of Elliptic Curves", 2nd edition (call it [S]). On p. 273 of [S] the author is considering an elliptic curve $E/K$ defined over a numbe …
Kestutis Cesnavicius's user avatar
15 votes
Accepted

Do there exist elliptic curves over schemes which have all primes as residue characteristics?

Yes, there can. Choose any elliptic curve $E$ over $\mathbb{Q}$ with potential good reduction (for instance, a curve with potential CM) and pass to a number field $K$ over which the reduction is every …
Kestutis Cesnavicius's user avatar
2 votes
Accepted

Interpreting Frobenius pullback as an invariant differential in the case of an elliptic curve

This is explained in the proof of Theorem 3 of section 15 of Mumford's "Abelian varieties" (pages 138-140 in the new edition) in the case when the base is an algebraically closed field of characterist …
Kestutis Cesnavicius's user avatar
13 votes
Accepted

$\lambda$-invariant is constant for isogenous elliptic curves

Given the brevity of the question, I am not sure about the precise setup, so let me assume that you are looking at some $\mathbf{Z}_p$-extension and that you assume (or know in the situation at hand) …
Kestutis Cesnavicius's user avatar
4 votes
Accepted

Rational points and torsion points of CM elliptic curve

See Cor. 5.18 of Rubin "Elliptic curves with complex multiplication" in LNM 1716 for a proof (that uses the main theorem of complex multiplication).
Kestutis Cesnavicius's user avatar
10 votes

Elliptic curve and Galois representation

None of these conditions implies that $E$ has good reduction at $p$. Consider, for instance, the elliptic curve $E = X_0(11)$, for which $E[5] \cong \mathbb{Z}/5\mathbb{Z} \oplus \mu_5$. Then for $l = …
Kestutis Cesnavicius's user avatar
6 votes

Elliptic curve E and Galois representation

Both questions have incorrect expectations. This has already been noted for the second question by S. Carnahan in the comments. For the first question, take any elliptic curve for which the semisimpli …
Kestutis Cesnavicius's user avatar
5 votes

Explicit calculation of Weil Deligne representations

Yes, it is possible. For all this explained clearly and in detail, see David Rohrlich's paper "Elliptic curves and the Weil-Deligne group" along with the accompanying "Student's supplement to "Ellipti …
Kestutis Cesnavicius's user avatar