Multiple recurrence conjecture for multiplicative actions and linearly factorable rational polynomials

Let (X,X,μ,Tn)(X,\mathcal X,\mu,T_n) be a finitely generated multiplicative action, and let R1,,RR_1,\ldots,R_\ell be rational polynomials that factor linearly. Suppose there exist m0,n0Zm_0,n_0\in\mathbb Z such that Rj(m0,n0)=1R_j(m_0,n_0)=1 for j=2,,j=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 AXA\in\mathcal X with μ(A)>0\mu(A)>0, consider

lim infNEm,n[N]μ(ATR1(m,n)1ATR(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,,j=1,\ldots,\ell for some m0,n0Zm_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.

Sources & referencesView supporting material

Primary source

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

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