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

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 tQt\in\mathbb{Q}, and define at(p)a_t(p) by

p+1at(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)=1pt=0p1at(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=limQlogQQpQAE(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 pQp\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.

Sources & referencesView supporting material

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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