Delaunay's moment conjecture for Tate–Shafarevich groups

Let pp be a prime. For a finite abelian pp-group of type λ\lambda, let Cλ,μ(p2)C_{\lambda,\mu}(p^2) denote the corresponding subgroup-counting polynomial evaluated at p2p^2. Let Fu{\mathcal F}_u be the family of elliptic curves E/QE/\mathbb Q of Mordell–Weil rank uu, ordered by conductor, and write \tencyr\cyraccSh(E)[pj]\text{\tencyr\cyracc{Sh}}(E)[p^j] for the subgroup of the Tate–Shafarevich group annihilated by pjp^j.

Delaunay's moment conjecture. For every positive integer \ell, partition λ=1m12m2m\lambda=1^{m_1}2^{m_2}\cdots \ell^{m_\ell}, and nonnegative integer uu, the average over EFuE\in{\mathcal F}_u satisfies

AvgEFuj=1\tencyr\cyraccSh(E)[pj]mj=μλCλ,μ(p2)pμ(2u1).\operatorname{Avg}_{E\in{\mathcal F}_u}\,\prod_{j=1}^{\ell}|\text{\tencyr\cyracc{Sh}}(E)[p^j]|^{m_j}=\sum_{\mu\subseteq\lambda}C_{\lambda,\mu}(p^2)p^{-|\mu|(2u-1)}.

This extends Cohen–Lenstra-type moment predictions to Tate–Shafarevich groups in fixed-rank families of elliptic curves. The source states it as a conjecture and gives no resolution.

Sources & referencesView supporting material

Primary source

Christophe Delaunay and Frédéric Jouhet, “The Cohen-Lenstra heuristics, moments and p^j-ranks of some groups”, arXiv:1303.7337 (2013).

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