Finitary Khintchine-type recurrence conjecture for finite abelian groups

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Let GG be a finite abelian group of order NN, let End(G)\textup{End}(G) denote its endomorphism ring, and let A⊆GA\subseteq G. For α,ε>0\alpha,\varepsilon>0, write N0=N0(α,ε)N_0=N_0(\alpha,\varepsilon) for a threshold depending only on these parameters. Finitary recurrence conjecture. For every α,ε>0\alpha,\varepsilon>0, there exists N0=N0(α,ε)N_0=N_0(\alpha,\varepsilon) such that, whenever N≥N0N\geq N_0, φ,ψ∈End(G)\varphi,\psi\in\textup{End}(G) satisfy that ψ−φ\psi-\varphi is an automorphism, and ∣A∣≥αN|A|\geq\alpha N, there exists y∈G∖{0}y\in G\setminus\{0\} such that

∣{x∈G:{x,x+φ(y),x+ψ(y)}⊆A}∣>(α3−ε)N.\left|\left\{x\in G:\{x,x+\varphi(y),x+\psi(y)\}\subseteq A\right\}\right|>(\alpha^3-\varepsilon)N.

This is the proposed finitary analogue of the infinite-group recurrence result, which gives syndetically many parameters with almost the expected density of three-term configurations. Its status is not resolved in the supplied text.

References

Primary source

Ethan Ackelsberg, “Khintchine-type double recurrence in abelian groups”, arXiv:2307.04698 (2024).

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