English

Pointwise convergence of some multiple ergodic averages

Dynamical Systems 2016-09-09 v1

Abstract

We show that for every ergodic system (X,μ,T1,,Td)(X,\mu,T_1,\ldots,T_d) with commuting transformations, the average 1Nd+10n1,,ndN10nN1f1(T1nj=1dTjnjx)f2(T2nj=1dTjnjx)fd(Tdnj=1dTjnjx).\frac{1}{N^{d+1}} \sum_{0\leq n_1,\ldots,n_d \leq N-1} \sum_{0\leq n\leq N-1} f_1(T_1^n \prod_{j=1}^d T_j^{n_j}x)f_2(T_2^n \prod_{j=1}^d T_j^{n_j}x)\cdots f_d(T_d^n \prod_{j=1}^d T_j^{n_j}x). converges for μ\mu-a.e. xXx\in X as NN\to\infty. If XX is distal, we prove that the average 1Ni=0Nf1(T1nx)f2(T2nx)fd(Tdnx)\frac{1}{N}\sum_{i=0}^{N} f_1(T_1^nx)f_2(T_2^nx)\cdots f_d(T_d^nx) converges for μ\mu-a.e. xXx\in X as NN\to\infty. We also establish the pointwise convergence of averages along cubical configurations arising from a system commuting transformations. Our methods combine the existence of sated and magic extensions introduced by Austin and Host respectively with ideas on topological models by Huang, Shao and Ye.

Keywords

Cite

@article{arxiv.1609.02529,
  title  = {Pointwise convergence of some multiple ergodic averages},
  author = {Sebastián Donoso and Wenbo Sun},
  journal= {arXiv preprint arXiv:1609.02529},
  year   = {2016}
}
R2 v1 2026-06-22T15:44:16.311Z