In Baraka's paper [2], he obtained the Littlewood-Paley characterization of Campanato spaces $L^{ 2,\lambda}$ and introduced $\mathcal { L}^{ p,\lambda,s}$ spaces. He showed that $\mathcal { L}^{ 2,\lambda,s}=(-\triangle)^{ -\frac{ s}{ 2}}L^{ 2,\lambda}$ for $0\leq\lambda<n+2$. In [7], by using the properties of fractional Carleson measures, J Xiao proved that for $n\geq2$, $0<\alpha<1$. $(-\triangle)^{ -\frac{ \alpha}{ 2}}L^{ 2,n-2\alpha}$ is essential the $Q_{ \alpha}(\mathbb{ R}^n)$ spaces which were introduced in [4]. Then we could conclude that $Q_{ \alpha}(\mathbb{ R}^n)=\mathcal { L}^{ 2,n-2\alpha,\alpha}$ for $0<\alpha<1$. In fact, this result could be also obtained directly by using the method in [2]. In this paper, We proved this result in the spirit of [2]. This paper could be considered as the supplement of Baraka's work [2].
Categories: math.CA