Nagao's conjecture for the rank of an elliptic curve over Q(T)\mathbb{Q}(T)

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Let E\mathcal{E} be an elliptic curve over Q(T)\mathbb{Q}(T) as in the source. For each prime pp, let Et\mathcal{E}_t denote the elliptic curve over Q\mathbb{Q} obtained by specializing TT at t∈Qt\in\mathbb{Q}, and define at(p)a_t(p) by

p+1−at(p)=#Et(Fp)p+1-a_t(p)=\#\mathcal{E}_t(\mathbb{F}_p)

unless pp divides the discriminant of Et\mathcal{E}_t, in which case at(p)=0a_t(p)=0. Set

AE(p)=1p∑t=0p−1at(p).A_{\mathcal{E}}(p)=\frac{1}{p}\sum_{t=0}^{p-1}a_t(p).

Nagao's conjecture. The rank rr of E(Q(T))\mathcal{E}(\mathbb{Q}(T)) satisfies

r=lim⁡Q→∞log⁡QQ∑p≤Q−AE(p),r=\lim_{Q\rightarrow\infty}\frac{\log Q}{Q}\sum_{p\leq Q}-A_{\mathcal{E}}(p),

where the sum runs over all primes p≤Qp\leq Q. The conjecture relates the Mordell–Weil rank over the function field to averaged point-counting data of the specialized elliptic curves. It was proven by Rosen and Silverman for rational elliptic surfaces, while the general formulation remains beyond that result.

References

Primary source

Francesco Battistoni, Sandro Bettin and Christophe Delaunay, “Ranks of elliptic curves over Q(T) of small degree in T”, arXiv:2109.00738 (2021).

Additional references

3 papers in this index state this conjecture (2016–2021). The statement above is taken from the most recent of them; the others are arXiv:1712.02775, arXiv:1612.03095.

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