Order of rank bias for rational elliptic curves

Let pp be a fixed prime. For each of the families Epr\mathcal E_{\mathrm{pr}}, Eall\mathcal E_{\mathrm{all}}, and Eht\mathcal E_{\mathrm{ht}}, let Er(X)\mathcal E_r(X) denote the curves of rank rr with size less than XX, and define

Ar(p,X;ϕ)=1#Er(X)EEr(X),E<X,(NE,p)=1ap(E)ϕ(NE).\mathcal A_r(p,X;\phi)=\frac{1}{\#\mathcal E_r(X)}\sum_{E\in\mathcal E_r(X),\,|E|<X,\,(N_E,p)=1}a_p(E)\phi(N_E).

Order of rank bias. If r0r\geq0 and Er\mathcal E_r is infinite, then there exists δ>0\delta>0 such that, for every ϵ>0\epsilon>0, if ϕ(N)(logN)δϵ\phi(N)\ll(\log N)^{\delta-\epsilon} then Ar(p,X;ϕ)0\mathcal A_r(p,X;\phi)\to0, while if ϕ(N)(logN)δϵ\phi(N)\gg(\log N)^{\delta-\epsilon} then Ar(p,X;ϕ)|\mathcal A_r(p,X;\phi)|\to\infty; moreover, the limit is ++\infty for r1r\leq1 and -\infty for r2r\geq2. This asserts that the rank bias has inverse polylogarithmic order in the conductor, subject to the stated infinitude hypothesis.

Sources & referencesView supporting material

Primary source

Kimball Martin and Thomas Pharis, “Rank bias for elliptic curves mod p”, arXiv:2103.02115 (2021).

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