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    A characterization of two weight norm inequality for Littlewood-Paley gΞ»βˆ—g_{\lambda}^{*}-function

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    Let nβ‰₯2n\ge 2 and gΞ»βˆ—g_{\lambda}^{*} be the well-known high dimensional Littlewood-Paley function which was defined and studied by E. M. Stein, \begin{align*} g_{\lambda}^{*}(f)(x) =\bigg(\iint_{\mathbb R^{n+1}_{+}} \Big(\frac{t}{t+|x-y|}\Big)^{n\lambda} |\nabla P_tf(y,t)|^2 \frac{dy dt}{t^{n-1}}\bigg)^{1/2}, \ \quad \lambda > 1, \end{align*} where Ptf(y,t)=ptβˆ—f(y)P_tf(y,t)=p_t*f(y), pt(y)=tβˆ’np(y/t)p_t(y)=t^{-n}p(y/t) and p(x)=(1+∣x∣2)βˆ’(n+1)/2p(x) = (1+|x|^2)^{-(n+1)/2}, βˆ‡=(βˆ‚βˆ‚y1,…,βˆ‚βˆ‚yn,βˆ‚βˆ‚t)\nabla =(\frac{\partial}{\partial y_1},\ldots,\frac{\partial}{\partial y_n},\frac{\partial}{\partial t}). In this paper, we give a characterization of two-weight norm inequality for gΞ»βˆ—g_{\lambda}^{*}-function. We show that, βˆ₯gΞ»βˆ—(fΟƒ)βˆ₯L2(w)≲βˆ₯fβˆ₯L2(Οƒ)\big\| g_{\lambda}^{*}(f \sigma) \big\|_{L^2(w)} \lesssim \big\| f \big\|_{L^2(\sigma)} if and only if the two-weight Muchenhoupt A2A_2 condition holds, and a testing condition holds : \begin{align*} \sup_{Q : cubes \ in \mathbb R^n} \frac{1}{\sigma(Q)} \int_{\mathbb R^n} \iint_{\widehat{Q}} \Big(\frac{t}{t+|x-y|}\Big)^{n\lambda}|\nabla P_t(\mathbf{1}_Q \sigma)(y,t)|^2 \frac{w dx dt}{t^{n-1}} dy < \infty, \end{align*} where Q^\widehat{Q} is the Carleson box over QQ and (w,Οƒ)(w, \sigma) is a pair of weights. We actually prove this characterization for gΞ»βˆ—g_{\lambda}^{*}-function associated with more general fractional Poisson kernel pΞ±(x)=(1+∣x∣2)βˆ’(n+Ξ±)/2p^\alpha(x) = (1+|x|^2)^{-{(n+\alpha)}/{2}}. Moreover, the corresponding results for intrinsic gΞ»βˆ—g_{\lambda}^*-function are also presented.Comment: 21 pages, to appear in Journal of Geometric Analysi
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