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arXiv 2112.03322math.DSmath.CA
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幂零群上的多项式平均和点态遍历定理

Polynomial averages and pointwise ergodic theorems on nilpotent groups

Alexandru D. Ionescu, Ákos Magyar, Mariusz Mirek, Tomasz Z. Szarek

摘要:

在$σ$ -有限测度空间上,建立了保测变换第二步的幂零群中多项式序列遍历平均的点态几乎处处收敛性.建立了相应的$L^p$上的极大不等式(对于$1<p\leq \infty$)和$L^2$上的$ρ$ -变分不等式(对于$2<ρ<\infty$).这在第二步的离散幂零群幂群中的所有多项式遍历平均的线性情形下对Furstenberg-Bergelson-Leibman猜想给出了肯定的回答。我们的证明是基于几乎正交技术,远远超出傅立叶变换工具,这是不可用的非交换,幂零设置。特别是,我们开发了我们所谓的幂零圈方法,使我们能够适应一些思想的经典圈方法的设置幂零群。

英文摘要:

We establish pointwise almost everywhere convergence for ergodic averages along polynomial sequences in nilpotent groups of step two of measure-preserving transformations on $σ$-finite measure spaces. We also establish corresponding maximal inequalities on $L^p$ for $1<p\leq \infty$ and $ρ$-variational inequalities on $L^2$ for $2<ρ<\infty$. This gives an affirmative answer to the Furstenberg-Bergelson-Leibman conjecture in the linear case for all polynomial ergodic averages in discrete nilpotent groups of step two. Our proof is based on almost-orthogonality techniques that go far beyond Fourier transform tools, which are not available in the non-commutative, nilpotent setting. In particular, we develop what we call a nilpotent circle method that allows us to adapt some of the ideas of the classical circle method to the setting of nilpotent groups.

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