Multiple recurrence conjecture for multiplicative actions and linearly factorable rational polynomials

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Let (X,X,μ,Tn)(X,\mathcal X,\mu,T_n) be a finitely generated multiplicative action, and let R1,…,RℓR_1,\ldots,R_\ell be rational polynomials that factor linearly. Suppose there exist m0,n0∈Zm_0,n_0\in\mathbb Z such that Rj(m0,n0)=1R_j(m_0,n_0)=1 for j=2,…,ℓj=2,\ldots,\ell, and either R1(m0,n0)=1R_1(m_0,n_0)=1 or (m0,n0)(m_0,n_0) is a simple zero of R1R_1. For A∈XA\in\mathcal X with μ(A)>0\mu(A)>0, consider

lim inf⁡N→∞Em,n∈[N]μ(A∩TR1(m,n)−1A∩⋯∩TRℓ(m,n)−1A).\liminf_{N\to\infty}\mathbb E_{m,n\in[N]}\mu\bigl(A\cap T^{-1}_{R_1(m,n)}A\cap\cdots\cap T^{-1}_{R_\ell(m,n)}A\bigr).

Multiple recurrence conjecture. This liminf is positive. Furthermore, if all the rational polynomials have degree 00 and Rj(m0,n0)=1R_j(m_0,n_0)=1 for j=1,…,ℓj=1,\ldots,\ell for some m0,n0∈Zm_0,n_0\in\mathbb Z, then the conclusion holds for all multiplicative actions. The conjecture generalizes the known one-polynomial case, which follows from results cited in the source. It predicts multiple recurrence for substantially broader polynomial patterns, while the case of several polynomials remains open.

References

Primary source

Nikos Frantzikinakis, “Decomposition results for multiplicative actions and applications”, arXiv:2503.15175 (2025).

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