Quantitative weighted bounds for the $q$-variation of singular integrals with rough kernels

TL;DR

This paper establishes the best known quantitative weighted bounds for the $q$-variation of singular integrals with rough kernels, extending previous results and providing new bounds of independent interest.

Contribution

It introduces new quantitative weighted bounds for $q$-variation operators with rough kernels, improving upon existing bounds and exploring their sharpness.

Findings

Established bounds for $V_qigrace T_{oldsymbol{ ext{Ω,ε}}}igrace$ operators

Derived bounds for convolutions with smooth functions $oldsymbol{ ext{φ}_k}$

Provided bounds for the $oldsymbol{ ext{S}_q}$ operator with sharpness results

Abstract

In this paper, we study the quantitative weighted bounds for the $q$-variational singular integral operators with rough kernels. The main result is for the sharp truncated singular integrals itself $$ \|V_q\{T_{\Omega,\varepsilon}\}_{\varepsilon>0}\|_{L^p(w)\rightarrow L^p(w)}\leq c_{p,q,n} \|\Omega\|_{ L^\infty}(w)_{A_p}^{1+1/q}\{w\}_{A_p},$$ where the quantity $(w)_{A_p}$, $\{w\}_{A_p}$ will be recalled in the introduction; we do not know whether this is sharp, but it is the best known quantitative result for this class of operators, since when $q=\infty$, it coincides with the best known quantitative bounds by Di Pilino--Hyt\"{o}nen--Li or Lerner. In the course of establishing the above estimate, we obtain several quantitative weighted bounds which are of independent interest. We hereby highlight two of them. The first one is $$ \|V_q\{\phi_k\ast T_{\Omega}\}_{k\in\mathbb Z}\|_{L^p(w)\rightarrow L^p(w)}\leq c_{p,q,n} \|\Omega\|_{ L^\infty}(w)_{A_p}^{1+1/q}\{w\}_{A_p},$$ where $\phi_k(x)=\frac1{2^{kn}}\phi(\frac x{2^k})$ with $\phi\in C^\infty_c(\mathbb R^n)$ being any non-negative radial function, and the sharpness for $q=\infty$ is due to Lerner; the second one is $$ \|\mathcal{S}_q\{T_{\Omega,\varepsilon}\}_{\varepsilon>0}\|_{L^p(w)\rightarrow L^p(w)}\leq c_{p,q,n} \|\Omega\|_{ L^\infty}(w)_{A_p}^{1/q}\{w\}_{A_p},$$ and the sharpness for $q=\infty$ follows from the Hardy--Littlewood maximal function.