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Grid method for divergence of averages
Published online by Cambridge University Press: 11 April 2023
Abstract
In this paper, we will introduce the ‘grid method’ to prove that the extreme case of oscillation occurs for the averages obtained by sampling a flow along the sequence of times of the form $\{n^\alpha : n\in {\mathbb {N}}\}$, where $\alpha $ is a positive non-integer rational number. Such behavior of a sequence is known as the strong sweeping-out property. By using the same method, we will give an example of a general class of sequences which satisfy the strong sweeping-out property. This class of sequences may be useful to solve a long-standing open problem: for a given irrational $\alpha $, whether the sequence $(n^\alpha )$ is bad for pointwise ergodic theorem in $L^2$ or not. In the process of proving this result, we will also prove a continuous version of the Conze principle.
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- © The Author(s), 2023. Published by Cambridge University Press