arXiv subjects
Publications and source records attributed to Congwen Liu.
In this paper, we characterize compactness in terms of the Berezin transform and obtain an essential norm estimate for operators in the Toeplitz algebra on Bergman spaces of the Siegel upper half-space.
In this paper, we classify positive solutions to the CR Yamabe equation on the Heisenberg group $\mathbb{H}^n$. We show that all such solutions are Jerison-Lee bubbles, without imposing any finite-energy or a priori symmetry assumptions. This result can be regarded as an analogue for $\mathbb{H}^n$ of the celebrated Caffarelli-Gidas-Spruck classification theorem in $\mathbb{R}^n$. To establish this, we develop a systematic approach to implement the method of moving spheres in the setting of the Heisenberg group.
This paper aims to determine the predual of the Bergman space $A_\lambda^1$ on the Siegel upper half-space. To achieve this, a Bloch-type space $\widetilde{\calB}$ is introduced and studied, and some of its essential properties are established. We identify the little Bloch-type space $\widetilde{\calB}_0$ with the predual of $A_\lambda^1$ via a duality pairing.
This short note is motivated by an attempt to understand the distinction between the Laplace operator and the hyperbolic Laplacian on the unit ball of $\mathbb{R}^n$, regarding the Lipschitz continuity of the solutions to the corresponding Dirichlet problems. We investigate the Dirichlet problem \begin{equation*} \left\{\begin{array}{ll} Δ_{\vartheta} u = 0, & \text{ in }\, \mathbb{B}^n,\\ u=ϕ, & \text{ on }\, \mathbb{S}^{n-1}, \end{array}\right. \end{equation*} where \[ Δ_{\vartheta} := (1-|x|^2) \bigg\{ \frac {1-|x|^2} {4} Δ+ \vartheta \sum_{j=1}^n x_{j} \frac {\partial } {\partial x_j} + \vartheta \left( \frac {n}{2}-1- \vartheta \right) I\bigg\}. \] We show that the Lipschitz continuity of boundary data always implies the Lipschitz continuity of the solutions if $\vartheta > 0$, but does not when $\vartheta \leq 0$.
In this paper, we show that the Bergman functions on the Siegel upper half-space enjoy the following uniqueness property: if $f\in A_t^p(\calU)$ and $\bfL^α f\equiv 0$ for some nonnegative multi-index $α$, then $f\equiv 0$, where $\bfL^α:=(\bfL_1)^{α_1} \cdots (\bfL_n)^{α_n}$ with $\bfL_j = \frac{\partial }{\partial z_j} + 2i \bar{z}_j \frac{\partial }{\partial z_n}$ for $j=1,\ldots, n-1$ and $\bfL_n = \frac{\partial }{\partial z_n}$. As a consequence, we obtain a new integral representation for the Bergman functions on the Siegel upper half-space. In the end, as an application, we derive a result that relates the Bergman norm to a "derivative norm", which suggests an alternative definition of the Bloch space and a notion of the Besov spaces over the Siegel upper half-space.
We study the boundedness of Toeplitz operators $T_ψ$ with locally integrable symbols on weighted harmonic Bergman spaces over the unit ball of $\mathbb{R}^n$. Generalizing earlier results for analytic function spaces, we derive a general sufficient condition for the boundedness of $T_ψ$ in terms of suitable averages of its symbol. We also obtain a similar "vanishing" condition for compactness. Finally, we show how these results can be transferred to the setting of the standard weighted Bergman spaces of analytic functions.
This paper is concerned with the $L^p$ integrability of $N$-harmonic functions with respect to the standard weights $(1-|x|^2)^α$ on the unit ball $\mathbb{B}$ of $\mathbb{R}^n$, $n\geq 2$. More precisely, our goal is to determine the real (negative) parameters $α$, for which $(1-|x|^2)^{α/p} u(x) \in L^p(\mathbb{B})$ implies that $u\equiv 0$, whenever $u$ is a solution of the $N$-Laplace equation on $\mathbb{B}$. This question is motivated by the uniqueness considerations of the Dirichlet problem for the $N$-Laplacian $Δ^N$. Our study is inspired by a recent work of Borichev and Hedenmalm [Adv. Math., 264(2014), pp. 464-505], where a complete answer to the above question in the case $n=2$ is given for the full scale $0<p<\infty$. When $n\geq 3$, we obtain an analogous characterization for $\frac{n-2}{n-1}\leq p<\infty$, and remark that the remaining case can be genuinely more difficult. Also, we extend the remarkable cellular decomposition theorem of Borichev and Hedenmalm to all dimensions.
Based on the recently proved Khavinson conjecture, we establish an inequality of Schwarz-Pick type for harmonic functions on the unit ball of $\mathbb{R}^n$.
We give a complete proof of the generalized Khavinson conjecture which states that, for bounded harmonic functions on the unit ball of $\mathbb{R}^n$, the sharp constants in the estimates for their radial derivatives and for their gradients coincide.
We characterize bounded and compact positive Toeplitz operators defined on the Bergman spaces over the Siegel upper half-space.
We determine exactly when two classes of integral operators are bounded on weighted $L^p$ spaces over the Siegel upper half-space.
We characterize the $L^p-L^q$ boundedness of Bergman-type operators over the Siegel upper half-space. This extends a recent result of Cheng et. al. (Trans. Amer. Math. Soc. 369:8643--8662, 2017) to higher dimensions.
Suppose $n\geq 3$ and let $B$ be the open unit ball in $\mathbb{R}^n$. Let $φ: B\to B$ be a $C^2$ map whose Jacobian does not change sign, and let $ψ$ be a $C^2$ function on $B$. We characterize bounded weighted composition operators $W_{φ,ψ}$ acting on harmonic Hardy spaces $h^p(B)$. In addition, we compute the operator norm of $W_{φ,ψ}$ on $h^p(B)$ when $φ$ is a Möbius transformation of $B$.
We obtain several estimates for the $L^p$ operator norms of the Bergman and Cauchy-Szegö projections over the the Siegel upper half-space. As a by-product, we also determine the precise value of the $L^p$ operator norm of a family of integral operators over the Siegel upper half-space.
We obtain new two-sided norm estimates for the family of Bergman-type projections arising from the standard weights $(1-|z|^2)^α$ where $α>-1$. As $α\to -1$, the lower bound is sharp in the sense that it asymptotically agrees with the norm of the Riesz projection. The upper bound is estimated in terms of the maximal Bergman projection, whose exact operator norm we calculate. The results provide evidence towards a conjecture that was posed very recently by the first author.