2. School of Mathematics and Statistics, Xinyang Normal University, Xinyang 464000, Henan, China
2. 信阳师范学院数学与统计学院, 河南信阳 464000
Hausdorff operator[1] was first introduced in 1917. As is well known, the Hausdorff operator includes many famous operators such as Hardy operator, adjoint Hardy operator, Cesaro operator and Hardy-Littlewood-Polya operator (see the examples below). Especially, Hardy operator as a kind of very important average operator is widely studied by many mathematicians. Researchers have built a relatively complete and mature theory about Hardy operator. Naturally, an in-depth study on Hausdorff operator is of great significance. In the recent years, Hausdorff operator and its variations have been widely studied by many researchers. For example, Chen et al.[2-3] considered the boundedness properties of Hausdorff operator on Euclidean spaces, such as the Lebesgue spaces Lp, the Hardy spaces Hp and the Herz type spaces. For the sake of convenience, one can refer to Refs. [4-8] for more details of the recent progress on Hausdorff operators. In 2015, Gao et al.[9] studied the boundness properties of the (fractional) Hausdorff operators on the Lebesgue spaces Lp with powers. It is the starting point of our research.
1 Preliminaries and main resultsWe first recall the classical one-dimensional Hausdorff operator. For a function ϕ defined on
$ h_{\phi}(f)(x)=\int_{0}^{\infty} \frac{\phi(y)}{y} f\left(\frac{x}{y}\right) \mathrm{d} y, \quad x \in \mathbb{R}. $ |
It is worth mentioning that if we choose different ϕ, then we will get different operators. Here we present several important examples that have been extensively studied.
$ \begin{aligned} &h_{\phi}(f)(x)= \\ &\left\{\begin{array}{l} \frac{1}{x} \int_{0}^{x} f(y) \mathrm{d} y, x \neq 0, \text { if } \phi(y)=\frac{\chi_{(1, \infty)}(y)}{y} ; \\ \int_{x}^{\infty} \frac{f(y)}{y} \mathrm{~d} y, \text { if } \phi(y)=\chi_{(0,1)}(y) ; \\ \int_{0}^{1} \frac{(1-y)^{\delta-1}}{y} f\left(y^{-1} x\right) \mathrm{d} y, \text { if } \phi(y)=\frac{\chi_{(0,1)}(y)}{(1-y)^{-\delta}}; \\ \int_{0}^{\infty} \frac{f(y)}{\max (y, x)} \mathrm{d} y, \text { if } \phi(y)=\chi_{(0,1)}(y)+\frac{\chi_{(1, \infty)}(y)}{y}. \end{array}\right. \end{aligned} $ |
Here, with the different choice of ϕ, hϕ represents the famous Hardy operator, adjoint Hardy operator, Cesaro operator and Hardy-Littlewood-Polya operator, respectively.
High-dimensional Hausdorff operators have several versions (see Refs. [2, 4, 6]). In 2003, Anderson[10] studied the n-dimensonal Hausdorff operator
$ H_{\Phi} f(x)=\int_{\mathbb{R}^{n}} \frac{\Phi(x /|y|)}{|y|^{n}} f(y) \mathrm{d} y, $ |
where Φ is a function defined on
In this paper we will consider the following n-dimensional Hausdorff operator. Give a nonnegative function Φ defined on
$ \mathscr{H}_{\Phi} f(x)=\int_{\mathbb{R}^{n}} \frac{\Phi(y)}{|y|^{n}} f\left(\frac{x}{|y|}\right) \mathrm{d} y. $ |
Our main purpose of this paper is to study the sharp bound of the Hausdorff operators
Before stating our main results, we give some ordinary notations as follows. For a∈
Definition 1.1 Let 1≤p < ∞, -1/p≤λ < 0, ω=ω(x)=|x|α and α≥0. The Morrey space with power weights Lp, λ(
$ \begin{aligned} &L^{p, \lambda}\left(\mathbb{R}^{n},|x|{ }^{\alpha} \mathrm{d} x\right) \\ &:=\left\{f \in L_{\mathrm{loc}}^{p}\left(\mathbb{R}^{n},|x|{ }^{\alpha} \mathrm{d} x\right):\right. \\ &\left.\quad\|f\|_{L^{p, \lambda}\left(\mathbb{R}^{n},|x|^{\alpha} \mathrm{d} x\right)}<+\infty\right\}, \end{aligned} $ |
where
$ \begin{aligned} &\|f\|_{L^{p, \lambda}\left(\mathbb{R}^{n},|x|^{\alpha} \mathrm{d} x\right)}= \\ &\sup \limits_{a \in \mathbb{R}^{n}, R>0}\left(\frac{1}{\omega(Q(a, R))^{1+p \lambda}} \int_{Q(a, R)}|f(x)|^{p}|x|^{\alpha} \mathrm{d} x\right)^{\frac{1}{p}} . \end{aligned} $ |
Definition 1.2 Let 1≤p < ∞, -1/p≤λ < 0, ω=ω(x)=|x|α and α≥0. The homogeneous central Morrey space with power weights
$ \begin{aligned} &\dot{B}{}^{p, \lambda}\left(\mathbb{R}^{n},|x|{ }^{\alpha} \mathrm{d} x\right) \\ &:=\left\{f \in L_{\mathrm{loc}}^{p}\left(\mathbb{R}^{n},|x|^{\alpha} \mathrm{d} x\right):\|f\|_{\dot{B}{}^{p, \lambda}\left(\mathbb{R}^{n},|x|^{\alpha} \mathrm{d} x\right)}<+\infty\right\}, \end{aligned} $ |
where
$ \begin{aligned} &\|f\|_{\dot{B}{}^{p, \lambda}\left(\mathbb{R}^{n},|x|^{\alpha} \mathrm{d}x\right)}= \\ &\sup \limits_{R>0}\left(\frac{1}{\omega(B(0, R))^{1+p \lambda}} \int_{B(0, R)}|f(x)|^{p}|x|^{\alpha} \mathrm{d} x\right)^{\frac{1}{p}} . \end{aligned} $ |
Now we formulate our two main results about
Theorem 1.1 Let 1≤p < ∞, -1/p≤λ < 0 and α≥0. Then
$ C:=\int_{\mathbb{R}^{n}} \frac{\Phi(y)}{|y|^{n+(\alpha+n) \lambda}} \mathrm{d} y<\infty. $ |
Furthermore,
However, when we consider the boundedness of
Theorem 1.2 Let 1≤p < ∞, -1/p≤λ < 0 and α≥0. Then
$ C:=\int_{\mathbb{R}^{n}} \frac{\Phi(y)}{|y|^{n+(\alpha+n) \lambda}} \mathrm{d} y<\infty. $ |
Proposition 1.1 Let 1≤p < ∞ and -1/p≤λ < 0. Then
$C:=\int_{\mathbb{R}^{n}} \frac{\Phi(y)}{|y|^{n+n\lambda}} \mathrm{d} y<\infty. $ |
Furthermore,
Our results can be extended to product spaces. Let m, ni∈${\mathbb{N}}^ + $, 1≤i≤m. Φ(y1, …, ym) is a nonnegative function defined on
$ \begin{aligned} \mathscr{H}_{\Phi}^{m}(f)\left(x_{1}, \cdots, x_{m}\right)= \int_{\mathbb{R}^{n_1}} \ldots \int_{\mathbb{R}^{n_m}} \frac{\Phi\left(y_{1}, \cdots, y_{m}\right)}{\left|y_{1}\right|^{n_{1}} \cdots\left|y_{m}\right|^{n_{m}}} \times \\ & f\left(\frac{x_{1}}{\left|y_{1}\right|}, \cdots, \frac{x_{m}}{\left|y_{m}\right|}\right) \mathrm{d} y_{1} \cdots \mathrm{d} y_{m}, \end{aligned} $ |
where x=(x1, …, xm)∈
For the sake of convenience, we use the following notations.
Let n =(n1, …, nm),
Correspondingly, we define the product Morrey spaces with power weights.
Definition 1.3 Let 1≤p < ∞, m∈
$ \begin{aligned} &L^{p, \boldsymbol{\lambda}}\left(\mathbb{R}^{\boldsymbol{n}},|x|^{\boldsymbol{\alpha}} \mathrm{d} x\right) \\ &:=\left\{f \in L_{\mathrm{loc}}^{p}\left(\mathbb{R}^{\boldsymbol{n}},|x|^{\boldsymbol{\alpha}} \mathrm{d} x\right):\|f\|_{L^{p, \boldsymbol{\lambda}}\left(\mathbb{R}^{\boldsymbol{n}},|x|^{\boldsymbol{\alpha}} \mathrm{d} x\right)}\right. \\ & \ \ \ \ \ \ <+\boldsymbol{\infty}\}, \end{aligned} $ |
where
$ \begin{aligned} & {\|f\|_{L^{p, \boldsymbol{\lambda}}\left(\mathbb{R}^{\boldsymbol{n}},|x| ^{\boldsymbol{\alpha}}{\mathrm{d}x}\right)}=\sup \limits_{{a_{i} \in \mathbb{R}{}^{n_{i}}{R_{i}}>0}\atop{1 \leqslant i \leqslant m}}}{\left(\frac{1}{\prod\nolimits_{i=1}^{m} \omega_{i}\left(Q\left(a_{i}, R_{i}\right)\right)^{1+p \lambda_{i}}} \times \right.}\\ &\left.\int_{Q\left(a_{1}, R_{1}\right)} \cdots \int_{Q\left(a_{m}, R_{m}\right)}|f(x)|^{p}|x|^{\alpha} \mathrm{d} x\right)^{\frac{1}{p}}. \end{aligned} $ |
Definition 1.4 Let 1≤p < ∞, m∈
$ \begin{aligned} &\dot{B}{}^{p, \boldsymbol{\lambda}}\left(\mathbb{R}^{\boldsymbol{n}}, \ \ |x|{ }^{\boldsymbol{\alpha}} \mathrm{d} x\right) \\ &:=\left\{f \in L_{\mathrm{loc}}^{p}\left(\mathbb{R}^{\boldsymbol{n}},|x|^{\boldsymbol{\alpha}} \mathrm{d} x\right):\|f\|_{\dot{B}{}^{p, \boldsymbol{\lambda}}{\left(R^{\boldsymbol{n}},|x|\right.}^{\boldsymbol{\alpha}}{\mathrm{d}x)}}<+\boldsymbol{\infty}\right\}, \end{aligned} $ |
where
$ \begin{aligned} &\|f\|_{\dot{B}{}^{p, \boldsymbol{\lambda}}(\mathbb{R}^{\boldsymbol{n}},|x|^{\boldsymbol{\alpha}} {\mathrm{d} x)}}=\sup \limits_{R_{i}>0,1 \leqslant i \leqslant m}\left(\frac{1}{\prod\nolimits_{i=1}^{m} \omega_{i}\left(B\left(0, R_{i}\right)\right)^{1+p \lambda_{i}}}\right) \times \\ &\ \ \left.\int_{B\left(0, R_{1}\right)} \cdots \int_{B\left(0, R_{m}\right)}|f(x)|^{p}|x|^{\alpha} \mathrm{d} x\right)^{\frac{1}{p}}. \end{aligned} $ |
Now we formulate our two main results about
Theorem 1.3 Let 1≤p < ∞, -1/p≤λi < 0, λ=(λ1, …, λm).αi≥0 and 1≤i≤m. Then
$ \begin{aligned} &C_{m}:=\int_{\mathbb{R}^{n_{1}}} \cdots \int_{\mathbb{R}^{n_{m}}} \times \\ &\frac{\Phi\left(y_{1}, \cdots, y_{m}\right)}{\left|y_{1}\right|^{n_{1}+\left(\alpha_{1}+n_{1}\right) \lambda_{1}} \cdots\left|y_{m}\right|^{n_{m}+\left(\alpha_{m}+n_{m}\right) \lambda_{m}}} \mathrm{~d} y<\boldsymbol{\infty}. \end{aligned} $ |
Furthermore,
Theorem 1.4 Let 1≤p < ∞, -1/p≤λi < 0, λ=(λ1, …, λm), αi≥0 and 1≤i≤m. Then
$ \begin{aligned} C_{m}&:=\int_{\mathbb{R}^{n_{1}}} \cdots \int_{\mathbb{R}^{n_{m}}} \times \\ &\frac{\Phi\left(y_{1}, \cdots, y_{m}\right)}{\left|y_{1}\right|^{n_{1}+\left(\alpha_{1}+n_{1}\right) \lambda_{1}} \cdots\left|y_{m}\right|^{n_{m}+\left(\alpha_{m}+n_{m}\right) \lambda_{m}}} \mathrm{~d} y<\boldsymbol{\infty}. \end{aligned} $ |
Proof of Theorem 1.1 We first prove the sufficiency. Since
$ \begin{aligned} &\left\|\mathscr{H}_{\Phi}(f)\right\|_{\dot{B}{}^{p, \lambda}\left(\mathbb{R}^{n},|x|^{\alpha} \mathrm{d} x\right)} \\ &=\sup \limits_{R>0}\left(\frac{1}{\omega(B(0, R))^{1+p \lambda}} \int_{B(0, R)}\left|\mathscr{H}_{\Phi}(f)(x)\right|^{p}|x|^{\alpha} \mathrm{d} x\right)^{\frac{1}{p}} \\ &=\sup \limits_{R>0}\left(\frac{1}{\omega(B(0, R))^{1+p \lambda}} \int_{B(0, R)}\left|\int_{\mathbb{R}^{n}} \frac{\Phi(y)}{|y|^{n}} f\left(\frac{x}{|y|}\right) \mathrm{d} y\right|^{p} \times\right. \\ &\left.\quad|x|^{\alpha} \mathrm{d} x\right)^{\frac{1}{p}}\\ &\leqslant \sup \limits_{R>0} \int_{\mathbb{R}^{n}}\left(\frac{1}{\omega(B(0, R))^{1+p \lambda}} \int_{B(0, R)}\left|\frac{\Phi(y)}{|y|^{n}} f\left(\frac{x}{|y|}\right)\right|^{p} \times\right.\\ &\quad\left.|x|^{\alpha} \mathrm{d} x\right)^{\frac{1}{p}} \mathrm{~d} y \\ &= \sup \limits_{R>0} \int_{\mathbb{R}^{n}} \frac{\Phi(y)}{|y|^{n}}\left(\frac{1}{\omega(B(0, R))^{1+p \lambda}} \int_{B(0, R)}\left|f\left(\frac{x}{|y|}\right)\right|^{p} \times\right.\\ &\quad\left.|x|^{\alpha} \mathrm{d} x\right)^{\frac{1}{p}} \mathrm{~d} y \quad(x \mapsto|y| x)\\ &= \sup \limits_{R>0} \int_{\mathbb{R}^{n}} \frac{\Phi(y)}{|y|^{n+(n+\alpha) \lambda}}\left(\frac{1}{\omega(B(0, R /|y|))^{1+p \lambda}} \int_{B(0, R|y|)} \times\right.\\ &\quad\left.|f(x)|^{p}|x|^{\alpha} \mathrm{d} x\right){ }^{\frac{1}{p}} \mathrm{~d} y \\ &\leqslant \int_{\mathbb{R}^{n}} \frac{\Phi(y)}{|y|^{n+(n+\alpha) \lambda}}\|f\|_{\dot{B}{}^{p, \lambda}\left(\mathbb{R}^{n},|x|^{\alpha} \mathrm{d} x\right)} \\ &= C\|f\|_{\dot{B}{}^{p, \lambda}\left(\mathbb{R}^{n},|x|^{\alpha}\mathrm{d} x\right)}. \end{aligned} $ | (1) |
Hence
Next we prove the necessity. Since
$ \left\|\mathscr{H}_{\Phi}\right\|_{\dot{B}{}^{p, \lambda}\left(\mathbb{R}^{n},|x|^{\alpha} \mathrm{d} x\right) \rightarrow \dot{B}{}^{p, \lambda}(\mathbb{R}^{n},|x| ^{\alpha}{\mathrm{d} x})}<\infty. $ |
From (1), we can get that
$ \left\|\mathscr{H}_{\Phi}\right\|_{\dot{B}{}^{p, \lambda}\left(\mathbb{R}^{n},|x|^{\alpha} \mathrm{d} x\right) \rightarrow \dot{B}{}^{p, \lambda}(\mathbb{R}^{n},|x| ^{\alpha}{\mathrm{d} x})} \le C. $ | (2) |
If we take g(x)=|x|(α+n)λ, it is easy to check that g belongs to
$ \mathscr{H}_{\Phi}(g)(x)={Cg}(x). $ | (3) |
In fact, we have that
$ \mathscr{H}_{\Phi}(g)(x)=\int_{\mathbb{R}^{n}} \frac{\Phi(y)}{|y|^{n}} \frac{|x|^{(\alpha+n) \lambda}}{|y|^{(\alpha+n) \lambda}} \mathrm{d} y={Cg}(x). $ |
It follows that
$ \begin{aligned} &\|g\|_{\dot{B}{}^{p, \lambda}\left(\mathbb{R}^{n},|x|^{\alpha} \mathrm{d} x\right)}\\ &=\sup \limits_{R>0}\left(\frac{1}{\omega(B(0, R))^{1+p \lambda}} \int_{B(0, R)}|g(x)|^{p}|x|^{\alpha} \mathrm{d} x\right)^{\frac{1}{p}} \\ &=\sup \limits_{R>0}\left(\frac{1}{\left(\frac{\omega_{n-1}}{\alpha+n} R^{\alpha+n}\right)^{1+p \lambda}} \int_{B(0, R)}|x|^{(\alpha+n) \lambda p+\alpha} \mathrm{d} x\right) \\ &=\left(\left(\frac{\alpha+n}{\omega_{n-1}}\right)^{1+p \lambda} \frac{\omega_{n-1}}{(\alpha+n)(1+p \lambda)}\right)^{\frac{1}{p}}<\infty. \end{aligned} $ |
It implies from (3) that
$ \left\|\mathscr{H}_{\Phi}\right\|_{\dot{B}{}^{p, \lambda}\left(\mathbb{R}^{n},|x|^{\alpha} \mathrm{d}x\right) \rightarrow \dot{B}{}^{p, \lambda}\left(\mathbb{R}^{n},|x|^{\alpha} \mathrm{d} x\right)} \geqslant C . $ | (4) |
Combining (2) with (4) yields that
$ \left\|\mathscr{H}_{\Phi}\right\|_{\dot{B}{}^{p, \lambda}\left(\mathbb{R}^{n},|x|^{\alpha} \mathrm{d}x\right) \rightarrow \dot{B}{}^{p, \lambda}\left(\mathbb{R}^{n},|x|^{\alpha} \mathrm{d} x\right)}=C<\infty. $ |
Proof of Theorem 1.2 Since
$ C:=\int_{\mathbb{R}^{n}} \frac{\Phi(y)}{|y|^{n+(\alpha+n) \lambda}} \mathrm{d} y<\infty, $ |
it follows from Minkowski inequality that
$ \begin{aligned} &\left\|\mathscr{H}_{\Phi}(f)\right\|_{L^{p, \lambda}\left(\mathbb{R}^{n},|x|^{\alpha} \mathrm{d} x\right)} \\ &=\sup \limits_{a \in \mathbb{R}^{n}, R>0}\left(\frac{1}{\omega(Q(a, R))^{1+p \lambda}} \int_{Q(a, R)}\left|\mathscr{H}_{\Phi}(f)(x)\right|^{p} \times\right. \\ &\left.\quad|x|^{\alpha} \mathrm{d} x\right)^{\frac{1}{p}} \\ &=\sup \limits_{a \in \mathbb{R}^{n}, R>0}\left(\frac{1}{\omega(Q(a, R))^{1+p \lambda}} \int_{Q(a, R)} \left| \int_{\mathbb{R}^{n}} \frac{\Phi(y)}{|y|^{n}} \times\right.\right.\\ &\left.\left. \quad f\left(\frac{x}{|y|}\right) \mathrm{d} y\right|^{p}|x|^{\alpha} \mathrm{d} x\right)^{\frac{1}{p}} \\ &\leqslant \left.\quad \sup \limits_{a \in \mathbb{R}^{n}, R>0} \int_{\mathbb{R}^{n}}\left(\frac{1}{\omega(Q(a, R))^{1+p \lambda}} \int_{Q(a, R)} \right| \frac{\Phi(y)}{|y|^{n}} \times\right. \\ &\left.\left.\quad f\left(\frac{x}{|y|}\right) \mathrm{d} y\right|^{p}|x|^{\alpha} \mathrm{d} x\right)^{\frac{1}{p}} \mathrm{~d} y \\ &= \int_{\mathbb{R}^{n}} \frac{\Phi(y)}{|y|^{n}}\left(\frac{1}{\omega(Q(a, R))^{1+p \lambda}} \int_{Q(a, R)}\left|f\left(\frac{x}{|y|}\right)\right|^{p} \times\right. \\ &\left.\quad|x|^{\alpha} \mathrm{d} x\right)^{\frac{1}{p}} \mathrm{~d} y(x \mapsto|y| x)\\ &=\int_{\mathbb{R}^{n}} \frac{\Phi(y)}{|y|^{n}} \left( \frac{\omega\left(Q\left(\frac{a}{|y|}, \frac{R}{|y|}\right)\right)^{1+p \lambda}}{\omega(Q(a, R))^{1+p \lambda}} \frac{1}{\omega\left(Q\left(\frac{a}{|y|}, \frac{R}{|y|}\right)\right)^{1+p \lambda}} \times\right. \\ &\left.\quad \int_{Q\left(\frac{a}{|y|}, \frac{R}{|y|}\right)}|f(x)|^{p}|x|^{\alpha}|y|^{\alpha+n} \mathrm{~d} x\right)^{\frac{1}{p}} \mathrm{~d} y \\ &=\int_{\mathbb{R}^{n}} \frac{\Phi(y)}{|y|^{n}}\left( |y|^{-(\alpha+n) p \lambda} \frac{1}{\omega\left(Q\left(\frac{a}{|y|}, \frac{R}{|y|}\right)\right)^{1+p \lambda}} \times\right.\\ &\left.\quad \int_{Q\left(\frac{a}{|y|}, \frac{R}{|y|}\right)}|f(x)|^{p}|x|^{\alpha} \mathrm{d} x\right)^{\frac{1}{p}} \mathrm{~d} y \\ &\leqslant\ \int_{\mathbb{R}^{n}} \frac{\Phi(y)}{|y|^{n+(n+\alpha) \lambda}}\|f\|_{\dot{B}{}^{p, \lambda}\left(\mathbb{R}^{n},|x|^{\alpha} \mathrm{d} x\right)} \\ &=C\|f\|_{\dot{B}{}^{p, \lambda}\left(\mathbb{R}^{n},|x|^{\alpha} \mathrm{d}x\right)}. \end{aligned} $ |
Hence
Proof of Proposition 1.1 By Theorem 1.2 we merely need to prove the necessity. More precisely, we need to find a function g∈Lp, λ(
$ \frac{\left\|\mathscr{H}_{\Phi}(g)\right\|_{L^{p, \lambda}\left(\mathbb{R}^{n}, \mathrm{~d} x\right)}}{\|g\|_{L^{p, \lambda}\left(\mathbb{R}^{n}, \mathrm{~d} x\right)}}=C. $ |
Taking g(x)=|x|nλ, by Ref.[11], we can easily check g∈Lp, λ(
Case 1: if |a|>2R, then |x|>R. For
$ \begin{aligned} &\quad \frac{1}{|Q(a, R)|{ }^{1+p \lambda}} \int_{Q(a, R)}|x|{ }^{n \lambda p} \mathrm{~d} x \\ &\leqslant \frac{1}{|Q(a, R)|^{1+p \lambda}} \int_{Q(a, R)} R^{n \lambda p} \mathrm{~d} x=1. \end{aligned} $ |
Case 2: if |a| < R, then Q(a, R)⊂Q(0, 3R), we have
$ \begin{aligned} &\frac{1}{|Q(a, R)|^{1+p \lambda}} \int_{Q(a, R)}|x|{ }^{n \lambda p} \mathrm{~d} x \\ &\leqslant \frac{1}{|Q(a, R)|^{1+p \lambda}} \int_{Q(0,3 R)} R^{n \lambda p} \mathrm{~d} x \\ &=\frac{|Q(0,3 R)|^{1+p \lambda}}{|Q(a, R)|^{1+p \lambda}} \frac{1}{|Q(0,3 R)|^{1+p \lambda}} \int_{Q(0,3 R)}|x|^{n \lambda p} \mathrm{~d} x \\ &=3^{n(1+p \lambda)} \frac{1}{|Q(0,3 R)|^{1+p \lambda}} \int_{Q(0,3 R)}|x|{ }^{n \lambda p} \mathrm{~d} x \\ &\leqslant 3^{n(1+p \lambda)}(\sqrt{n})^{n \lambda p} \\ &<+\infty . \end{aligned} $ |
Hence, g∈Lp, λ(
Proof of Theorem 1.3 We just prove the theorem for m=2. For m>3, the method is similar. We first prove the sufficiency.
Since C2 < ∞, by the definitions of
$ \begin{aligned} &\left\|\mathscr{H}_{\Phi}^{2}(f)\right\|_{\dot{B}{}^{p, \boldsymbol{\lambda}}\left(\mathbb{R}^{\boldsymbol{n}},|x|^{\boldsymbol{\alpha}} \mathrm{d} x\right)} \\ &=\sup \limits_{R_{1}, R_{2}>0}\left(\frac{1}{\prod\nolimits_{i=1}^{2} \omega_{i}\left(B\left(0, R_{i}\right)\right)^{1+p \lambda_{i}}} \int_{B\left(0, R_{1}\right)} \int_{B\left(0, R_{2}\right)} \times\right. \\ &\left.\quad\left|\mathscr{H}_{\Phi}^{2}(f)\left(x_{1}, x_{2}\right)\right|^{p}|x|^{\boldsymbol{\alpha}} \mathrm{d} x\right)^{\frac{1}{p}} \\ &=\sup \limits_{R_{1}, R_{2}>0}\left(\frac{1}{\prod\nolimits_{i=1}^{2} \omega_{i}\left(B\left(0, R_{i}\right)\right)^{1+p \lambda_{i}}} \int_{B\left(0, R_{1}\right)} \int_{B\left(0, R_{2}\right)} \left| \int_{\mathbb{R}}{ }_{n_{1}} \times\right. \right.\\ &\left.\left.\quad \int_{\mathbb{R}^{n_{2}}} \frac{\Phi\left(y_{1}, y_{2}\right)}{\left|y_{1}\right|^{n_{1}}\left|y_{2}\right|^{n_{2}}} f\left(\frac{x_{1}}{\left|y_{1}\right|}, \frac{x_{2}}{\left|y_{2}\right|}\right) \mathrm{d} y_{1} \mathrm{~d} y_{2}\right|^{p}|x|^{\boldsymbol{\alpha}} \mathrm{d} x\right)^{\frac{1}{p}}\\ &\leqslant \sup \limits_{R_{1}, R_{2}>0} \int_{\mathbb{R}^{n_{1}}} \int_{\mathbb{R}^{n_{2}}} \frac{\Phi\left(y_{1}, y_{2}\right)}{\left|y_{1}\right|^{n_{1}}\left|y_{2}\right|^{n_{2}}}\left(\frac{1}{\prod\nolimits_{i=1}^{2} \omega_{i}\left(B\left(0, R_{i}\right)\right)^{1+p \lambda_{i}}} \times\right. \\ &\quad \int_{\mathbb{R}^{n_{1}}} \int_{\mathbb{R}^{n_{2}}}\left|f\left(\frac{x_{1}}{\left|y_{1}\right|}, \frac{x_{2}}{\left|y_{2}\right|}\right)\right|^{p}\left|x_{1}\right|^{\alpha_{1}}\left|x_{2}\right|^{\alpha_{2}} \times \\ &\left.\quad \mathrm{d} x_{1} \mathrm{~d} x_{2}\right)^{\frac{1}{p}} \mathrm{~d} y_{1} \mathrm{~d} y_{2}\\ &=\sup \limits_{R_{1}, R_{2}>0} \int_{\mathbb{R}^{n_{1}}} \int_{\mathbb{R}^{n_{2}}} \frac{\Phi\left(y_{1}, y_{2}\right)}{\left|y_{1}\right|^{n_{1}+\left(\alpha_{1}+n_{1}\right) \lambda_{1}}\left|y_{2}\right|^{n_{2}+\left(\alpha_{2}+n_{2}\right) \lambda_{2}}} \times\\ &\quad\left(\frac{1}{\prod\nolimits_{i=1}^{2} \omega_{i}\left(B\left(0, \frac{R}{\left|y_{i}\right|}\right)\right)^{1+p \lambda_{i}}} \int_{B\left(0, \frac{R_{1}}{\mid y_{1}\mid}\right)} \int_{B\left(0, \frac{R_{2}}{\left|y_{2}\right|}\right)} \times\right.\\ &\quad\left.\left|f\left(x_{1}, x_{2}\right)\right|^{p}\left|x_{1}\right|^{\alpha_{1}}\left|x_{2}\right|^{\alpha_{2}} \mathrm{~d} x_{1} \mathrm{~d} x_{2}\right)^{\frac{1}{p}} \mathrm{~d} y_{1} \mathrm{~d} y_{2} \text {. } \end{aligned} $ |
Then we get
$ \begin{aligned} &\left\|\mathscr{H}_{\Phi}^{2}(f)\right\|_{\dot{B}{}^{p, \boldsymbol{\lambda}}\left(\mathbb{R}^{\boldsymbol{n}},|x|^{\boldsymbol{\alpha}} \mathrm{d} x\right) }\\ &\leqslant \sup \limits_{R_{1}, R_{2}>0} \int_{\mathbb{R}^{n_{1}}} \int_{\mathbb{R}^{n_{2}}} \frac{\Phi\left(y_{1}, y_{2}\right)}{\left|y_{1}\right|^{n_{1}+\left(\alpha_{1}+n_{1}\right) \lambda_{1}}\left|y_{2}\right|^{n_{2}+\left(\alpha_{2}+n_{2}\right) \lambda_{2}}} \times \\ &\quad\|f\|_{\dot{B}{}^{p, \boldsymbol{\lambda}}\left(\mathbb{R}^{\boldsymbol{n}},|x|^{\boldsymbol{\alpha}} \mathrm{d} x\right)} \\ &=C_{2}\|f\|_{\dot{B}{}^{p, \boldsymbol{\lambda}}\left(\mathbb{R}^{\boldsymbol{n}},|x|^{\boldsymbol{\alpha}} \mathrm{d} x\right)}. \end{aligned} $ |
Hence
Next we prove the necessity. Take
$ g\left(x_{1}, x_{2}\right)=\left|x_{1}\right|{ }^{\left(\alpha_{1}+n_{1}\right) \lambda_{1}}\left|x_{2}\right|^{\left(\alpha_{2}+n_{2}\right) \lambda_{2}}. $ |
By the similar consideration and computation of the necessity of Theorem 1.1, we can obtain our conclusion immediately.
Proof of Theorem 1.4 The proof of Theorem 1.4 is similar to the proof of Theorem 1.2, so we omit the details.
[1] |
Hurwitz W A, Silverman L L. On the consistency and equivalence of certain definitions of summability[J]. Transactions of the American Mathematical Society, 1917, 18(1): 1-20. DOI:10.1090/S0002-9947-1917-1501058-2 |
[2] |
Chen J C, Fan D S, Wang S L. Hausdorff operators on Euclidean spaces[J]. Applied Mathematics: A Journal of Chinese Universities Series B, 2013, 28(4): 548-564. DOI:10.1007/s11766-013-3228-1 |
[3] |
Chen J C, Dai J W, Fan D S, et al. Boundedness of Hausdorff operators on Lebesgue spaces and Hardy spaces[J]. Science China Mathematics, 2018, 61(9): 1647-1664. DOI:10.1007/s11425-017-9246-7 |
[4] |
Brown G, Móricz F. Multivariate Hausdorff operators on the spaces Lp(${\mathbb{R}}^n$)[J]. Journal of Mathematical Analysis and Applications, 2002, 271(2): 443-454. DOI:10.1016/S0022-247X(02)00128-2 |
[5] |
Chen J C, Fan D S, Zhang C J. Multilinear Hausdorff operators and their best constants[J]. Acta Mathematica Sinica, English Series, 2012, 28(8): 1521-1530. DOI:10.1007/s10114-012-1455-7 |
[6] |
Chen J C, Fan D S, Liu J. Hausdorff operators on function spaces[J]. Chinese Annals of Mathematics, Series B, 2012, 33(4): 537-556. DOI:10.1007/s11401-012-0724-1 |
[7] |
Lin X Y, Sun L J. Some estimates on the Hausdorff operator[J]. Acta Scientiarum Mathematicarum (Szeged), 2012, 78(3/4): 669-681. |
[8] |
Wu X M. Best constants for a class of Hausdorff operators on Lebesgue spaces[J]. Advances in Mathematics, 2017, 46(5): 793-800. |
[9] |
Gao G L, Wu X M, Guo W C. Some results for Hausdorff operators[J]. Mathematical Inequalities and Applications, 2015, 18(1): 155-168. |
[10] |
Andersen K F. Boundedness of Hausdorff operators on Lp(${\mathbb{R}}^n$), H1(${\mathbb{R}}^n$) and BMO(${\mathbb{R}}^n$)[J]. Acta Scientiarum Mathematicarum (Szeged), 2003, 69(1/2): 409-418. |
[11] |
Fu Z W, Grafakos L, Lu S Z, et al. Sharp bounds for m-linear Hardy and Hilbert operators[J]. Houston Journal of Mathematics, 2012, 38(1): 225-244. |