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Let $X$ be an abelian variety. In this question, that will mean that $X$ is a complex torus $\mathbb C^n / \Lambda$, where $\Lambda \subset \mathbb C^n$ is a lattice, and that $X$ also a projective variety. Does $X$ contain an elliptic curve?

The question comes from thinking about Demailly's definition of algebraic hyperbolicity. He said a projective variety $X$ is algebraically hyperbolic if for every Kahler class $\omega$ on $X$ there exists an $\varepsilon > 0$ such that if $C \subset X$ is a curve and $\widetilde C$ is its normalization we have $$ \varepsilon \leq \frac{g(\widetilde C)}{\deg_\omega C}. $$ Furthermore he proved that an abelian variety is not algebraically hyperbolic (because it admits a nonconstant map from an abelian variety, namely itself).

An idea for proving that a variety is not algebraically hyperbolic is to try to come up with a sequence of curves $(C_k)$ on $X$ such that $g(\widetilde C_k) / \deg_\omega C_k \to 0$. I'm wondering whether this works at all, or whether this ratio is generally bounded away from $0$ for curves that aren't simply rational or elliptic. If there exists an abelian variety that doesn't contain an elliptic curve, this idea must work sometimes.

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  • $\begingroup$ I guess not, at least not as a subgroup: if yes then there are $w_1,w_2\in \Lambda$ s.t. $\mathbb{R}$ span of them are complex, i.e. closed under multiplication by $\sqrt{-1}$, which in general not true. $\endgroup$ Commented Sep 17 at 8:50
  • $\begingroup$ It doesn’t have to be as a subgroup. $\endgroup$ Commented Sep 17 at 9:15
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    $\begingroup$ I just realize that it is a subgroup up to translation: say Corollary 1.2 in jmilne.org/math/CourseNotes/AV.pdf $\endgroup$ Commented Sep 17 at 9:24
  • $\begingroup$ @PeterWu Well, well, well! I think you can write that up as an answer if you want. $\endgroup$ Commented Sep 17 at 9:45
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    $\begingroup$ A word about terminology: by definition an abelian variety that doesn't contain any proper abelian subvariety is called simple. Searching online will turn up plenty of examples of simple abelian varieites. $\endgroup$ Commented Sep 17 at 10:31

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