Pinsker reduction conjecture for polynomial ergodic averages along primes

From papers

Let (X,B,μ,Zd)(X,\mathcal B,\mu,\mathbb Z^d) be a measure-preserving system generated by invertible transformations T1,,TdT_1,\ldots,T_d, and let pi,j(n)Z[n]p_{i,j}(n)\in\mathbb Z[n] be the polynomials from Theorem 1. Write Pμ(Zd)P_{\mu}(\mathbb Z^d) for the Pinsker σ\sigma-algebra, and let P={a0<a1<<an<}\mathbb P=\{a_0<a_1<\cdots<a_n<\cdots\} be the set of all prime numbers. Pinsker reduction conjecture. Under the assumptions of Theorem 1, for every f1,,fmL(X,B,μ)f_1,\ldots,f_m\in L^{\infty}(X,\mathcal B,\mu), the limit

limN1Nn=0N1j=1mfj(T1p1,j(an)Tdpd,j(an)x)\lim_{N\rightarrow\infty}\frac{1}{N}\sum_{n=0}^{N-1}\prod_{j=1}^{m}f_j\bigl(T_1^{p_{1,j}(a_n)}\cdots T_d^{p_{d,j}(a_n)}x\bigr)

exists almost everywhere if and only if, for every h1,,hmL(X,Pμ(Zd),μ)h_1,\ldots,h_m\in L^{\infty}(X,P_{\mu}(\mathbb Z^d),\mu), the limit

limN1Nn=0N1j=1mhj(T1p1,j(an)Tdpd,j(an)x)\lim_{N\rightarrow\infty}\frac{1}{N}\sum_{n=0}^{N-1}\prod_{j=1}^{m}h_j\bigl(T_1^{p_{1,j}(a_n)}\cdots T_d^{p_{d,j}(a_n)}x\bigr)

exists almost everywhere. The conjecture proposes that almost-everywhere convergence of these prime polynomial averages is completely determined by the Pinsker factor. The preceding theorem establishes this reduction for the special case in which each polynomial iterate uses only one transformation; the general case remains open in the source.

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Sources & referencesView supporting material

Primary source

Rongzhong Xiao, “Polynomial ergodic averages of measure-preserving systems acted by Z^d”, arXiv:2206.02197 (2023).

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