On Sharpness of $L$ log $L$ Criterion for Weak Type $(1,1)$ boundedness of rough operators

In this note, we show that the $\Omega \in L\log L$ hypothesis is the strongest size condition on a function $\Omega $ on the unit sphere with mean value zero, which ensures that the corresponding singular integral $T_\Omega $ defined by \[ T_{\Omega }f(x)=p.v.\int \frac{1}{|x-y|^d}\Omega \Bigl (\fr...

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Bibliographic Details
Main Author: Bhojak, Ankit
Format: Article
Language:English
Published: Académie des sciences 2024-11-01
Series:Comptes Rendus. Mathématique
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Online Access:https://comptes-rendus.academie-sciences.fr/mathematique/articles/10.5802/crmath.633/
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Summary:In this note, we show that the $\Omega \in L\log L$ hypothesis is the strongest size condition on a function $\Omega $ on the unit sphere with mean value zero, which ensures that the corresponding singular integral $T_\Omega $ defined by \[ T_{\Omega }f(x)=p.v.\int \frac{1}{|x-y|^d}\Omega \Bigl (\frac{x-y}{|x-y|}\Big )f(y)\, \mathrm{d} y,\] maps $L^1(\mathbb{R}^d)$ to weak $L^1(\mathbb{R}^d)$, provided $T_\Omega $ is bounded in $L^2(\mathbb{R}^d)$.
ISSN:1778-3569