Weak Endpoint Estimate for Commutators of Rough Maximal Singular Integral operators

Abstract

Let $d\geq 2$ and $T^*_{\Omega,b}$ be the commutator of the rough maximal singular integral on $\mathbb{R}^d$ defined by $$T^*_{\Omega,b}f(x)=\sup_{\varepsilon>0}\left|\int_{|x-y|>\varepsilon}\bigl(b(x)-b(y)\bigr)\frac{\Omega(x-y)}{|x-y|^d}f(y)\,dy\right|.$$ Assume that $\Omega\in L(\log L)^2(\mathbb{S}^{d-1})$ has mean zero and that $b\in\operatorname{BMO}(\mathbb{R}^d)$. We prove that, for every $\lambda>0$, \[\bigl|\{x\in\mathbb{R}^d:T^*_{\Omega,b}f(x)>\lambda\}\bigr|\lesssim_{\Omega,b}\int_{\mathbb{R}^d}\frac{|f(x)|}{\lambda}\log\!\left(e+\frac{|f(x)|}{\lambda}\right)\,dx.\] The argument starts from a Calder\'on-Zygmund decomposition of $f$ and a dyadic linearization of the maximal truncation. A decomposition of $\Omega$ by size, followed by regularization of the spatial cutoffs and a microlocal decomposition, reduces the problem to a family of estimates with quantitative decay. The required decay follows by interpolating localized $L^1$ and $L^3$ bounds and using an analytic-family argument for the commutators.