English

Complete convergence of the Hilbert transform

Classical Analysis and ODEs 2022-08-04 v9

Abstract

Suppose that {aj}1\{a_j\}\in \ell^1, and suppose that for any sequence (tn)(t_n) of integers there exits a constant C1>0C_1>0 such that {kZ:supn1iBntn ⁣ ⁣ ⁣\raise1.9ex  ak+ii>λ}C1{kZ:supn1iBn ⁣ ⁣\raise1.9ex  ak+ii>λ},\sharp\left\{k\in\mathbb{Z}:\sup_{n\geq 1}\left|\sum_{i\in \mathcal{B}_n-t_n} \!\!\!\raise{1.9ex}\hbox{$\scriptsize\prime$}\; \frac{a_{k+i}}{i}\right|>\lambda\right\}\\ \leq C_1\sharp\left\{k\in\mathbb{Z}:\sup_{n\geq 1}\left|\sum_{i\in \mathcal{B}_n} \!\!\raise{1.9ex}\hbox{$\scriptsize\prime$}\; \frac{a_{k+i}}{i}\right|>\lambda\right\}, for all λ>0\lambda >0, where Bn={n,(n1),(n2),,n2,n1,n}\mathcal{B}_n=\{-n, -(n-1), -(n-2),\dots , n-2, n-1, n\}. Then there is a constant C2>0C_2>0 which does not depend on the sequence {aj}\{a_j\} such that n=1{kZ:i=nn ⁣ ⁣\raise1.9ex  ak+ii>λ}C2λi=ai\sum_{n=1}^\infty\sharp\left\{k\in\mathbb{Z}:\left|\sum_{i=-n}^{n} \!\!\raise{1.9ex}\hbox{$\scriptsize\prime$}\; \frac{a_{k+i}}{i}\right|>\lambda\right\}\leq\frac{C_2}{\lambda}\sum_{i=-\infty}^{\infty}|a_i| for all λ>0\lambda>0. Let (X,B,μ)(X,\mathscr{B},\mu ) be a measure space, τ:XX\tau :X\to X an invertible measure-preserving transformation, and suppose that fL1(X)f\in L^1(X) such that for any sequence (tn)(t_n) of integers there exists a constant C1>0C_1>0 such that μ{x:supn1iBntn ⁣ ⁣ ⁣\raise1.9ex  f(τix)i>λ}C1μ{x:supn1iBn ⁣ ⁣\raise1.9ex  f(τix)i>λ}\mu\left\{ x: \sup_{n\geq 1}\left|\sum_{i\in \mathcal{B}_n-t_n}\!\!\!\raise{1.9ex}\hbox{$\scriptsize\prime$}\; \frac{f(\tau^ix)}{i}\right| >\lambda \right\}\leq C_1\mu\left\{x: \sup_{n\geq 1}\left|\sum_{i\in \mathcal{B}_n}\!\!\raise{1.9ex}\hbox{$\scriptsize\prime$}\; \frac{f(\tau^i x)}{i}\right|>\lambda \right\} for all λ>0\lambda >0, where Bn={n,(n1),(n2),,n2,n1,n}\mathcal{B}_n=\{-n, -(n-1), -(n-2),\dots , n-2, n-1, n\}. Then there exists a constant C2>0C_2>0 which does not depend on ff such that n=1μ{x:i=nn ⁣ ⁣\raise1.9ex  f(τix)i>λ}C2λf1\sum_{n=1}^\infty\mu\left\{x:\left|\sum_{i=-n}^{n}\!\!\raise{1.9ex}\hbox{$\scriptsize\prime$} \;\frac{f(\tau^ix)}{i}\right|>\lambda\right\}\leq\frac{C_2}{\lambda}\|f\|_1 for all λ>0\lambda >0.

Keywords

Cite

@article{arxiv.2009.05822,
  title  = {Complete convergence of the Hilbert transform},
  author = {Sakin Demir},
  journal= {arXiv preprint arXiv:2009.05822},
  year   = {2022}
}
R2 v1 2026-06-23T18:29:34.180Z