Cyclicity conjecture for elliptic curves

Let E/QE/\mathbb{Q} be a non-CM elliptic curve. For each positive integer kk, let E[k]E[k] be the kk-torsion subgroup and let Q(E[k])\mathbb{Q}(E[k]) be the field obtained by adjoining the coordinates of all points in E[k]E[k]. Define

πEcyc(x)=#{px:Ep(Fp) is cyclic}.\pi_E^{\mathrm{cyc}}(x)=\#\{p\leq x:E_p(\mathbb{F}_p)\text{ is cyclic}\}.

Here Ep/FpE_p/\mathbb{F}_p denotes the reduction of EE at a prime of good reduction, and μ\mu is the Möbius function. Cyclicity conjecture.

πEcyc(x)(k1μ(k)[Q(E[k]):Q])li(x).\pi_E^{\mathrm{cyc}}(x)\sim \left(\sum_{k\geq 1}\frac{\mu(k)}{[\mathbb{Q}(E[k]):\mathbb{Q}]}\right)\operatorname{li}(x).

This predicts the density of primes for which the group of points on the reduced elliptic curve is cyclic. The source gives no resolution status, so the conjecture is recorded as open.

Sources & referencesView supporting material

Primary source

Luke Fredericks, “Average Cyclicity for Elliptic Curves in Torsion Families”, arXiv:2101.06202 (2021).

Additional references

2 papers in this index state this conjecture (2007–2021). The statement above is taken from the most recent of them; the others are arXiv:0711.3484.

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