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Brett D. Wick

Publications and source records attributed to Brett D. Wick.

At least 91 records · Page 5Linked to original sources
arXiv2017

Localization and compactness of Operators on Fock Spaces

For $0<p\leq\infty$, let $F^{p}_φ$ be the Fock space induced by a weight function $φ$ satisfying $ dd^c φ\simeq ω_0$. In this paper, given $p\in (0, 1]$ we introduce the concept of weakly localized operators on $ F^{p}_φ$, we characterize the compact operators in the algebra generated by weakly localized operators. As an application, for $0<p<\infty$ we prove that an operator $T$ in the algebra generated by bounded Toeplitz operators with $\textrm{BMO}$ symbols is compact on $F^p_φ$ if and only if its Berezin transform satisfies certain vanishing property at $\infty$. In the classical Fock space, we extend the Axler-Zheng condition on linear operators $T$, which ensures $T$ is compact on $F^p_α$ for all possible $0<p<\infty$.

math.CV↗
arXiv2017

Weak factorization of Hardy spaces in the Bessel setting

We provide the weak factorization of the Hardy spaces $H^{p}(\mathbb{R}_+, dm_λ)$ in the Bessel setting, for $p\in \left(\frac{2λ+ 1}{2λ+ 2}, 1\right]$. As a corollary we obtain a characterization of the boundedness of the commutator $[b, R_{Δ_λ}]$ from $L^{q}(\mathbb{R}_+, dm_λ)$ to $L^{r}(\mathbb{R}_+, dm_λ)$ when $b\in \textrm{Lip}_α(\mathbb{R}_+, dm_λ)$ provided that $α= \frac{1}{q} - \frac{1}{r}$. The results are a slight generalization and modification of the work of Duong, Li, Yang, and the second named author, which in turn are based on modifications and adaptations of work by Uchiyama.

math.CA↗
arXiv2017

Product BMO, little BMO and Riesz Commutators in the Bessel setting

In this paper, we study the product BMO space, little bmo space and their connections with the corresponding commutators associated with Bessel operators studied by Weinstein, Huber, and by Muckenhoupt-Stein. We first prove that the product BMO space in the Bessel setting can be used to prove the boundedness of the iterated commutators with the Bessel Riesz transforms. We next study the little $\rm bmo$ space in this Bessel setting and obtain the equivalent characterization of this space in terms of commutators. We further show that in analogy with the classical setting, the little $\rm bmo$ space is a proper subspace of the product $\rm BMO$ space. These extend the previous related results studied by Cotlar-Sadosky and Ferguson-Sadosky on the bidisc to the Bessel setting.

math.CA↗
arXiv2017

Two weight commutators for Beurling--Ahlfors operator

We establish the equivalent characterisation of the weighted BMO space on the complex plane $\mathbb{C}$ via the two weight commutator of the Beurling--Ahlfors operator with a BMO function. Our method of proofs relies on the explicit kernel of the Beurling--Ahlfors operator and the properties of Muckenhoupt weight class.

math.CA↗
arXiv2017

Commutators, Little BMO and Weak Factorization

In this paper, we provide a direct and constructive proof of weak factorization of $h^1(\mathbb{R})$ (the predual of little BMO space bmo$(\mathbb{R}\times\mathbb{R})$ studied by Cotlar-Sadosky and Ferguson-Sadosky), i.e., for every $f\in h^1(\mathbb{R}\times\mathbb{R})$ there exist sequences $\{α_j^k\}\in\ell^1$ and functions $g_j^k,h^k_j\in L^2(\mathbb{R}^2)$ such that \begin{align*} f=\sum_{k=1}^\infty\sum_{j=1}^\inftyα^k_j\Big(\, h^k_j H_1H_2 g^k_j - g^k_j H_1H_2 h^k_j\Big) \end{align*} in the sense of $h^1(\mathbb{R})$, where $H_1$ and $H_2$ are the Hilbert transforms on the first and second variable, respectively. Moreover, the norm $\|f\|_{h^1(\mathbb{R}\times\mathbb{R})}$ is given in terms of $\|g^k_j\|_{L^2(\mathbb{R}^2)}$ and $\|h^k_j\|_{L^2(\mathbb{R}^2)}$. By duality, this directly implies a lower bound on the norm of the commutator $[b,H_1H_2]$ in terms of $\|b\|_{{\rm bmo}(\mathbb{R}\times\mathbb{R})}$. Our method bypasses the use of analyticity and the Fourier transform, and hence can be extended to the higher dimension case in an arbitrary $n$-parameter setting for the Riesz transforms.

math.CA↗
arXiv2017

The Corona Problem for Kernel Multiplier Algebras

We prove an alternate Toeplitz corona theorem for the algebras of pointwise kernel multipliers of Besov-Sobolev spaces on the unit ball in $\mathbb{C}^{n}$, and for the algebra of bounded analytic functions on certain strictly pseudoconvex domains and polydiscs in higher dimensions as well. This alternate Toeplitz corona theorem extends to more general Hilbert function spaces where it does not require the complete Pick property. Instead, the kernel functions $k_{x}\left(y\right)$ of certain Hilbert function spaces $\mathcal{H}$ are assumed to be invertible multipliers on $\mathcal{H}$, and then we continue a research thread begun by Agler and McCarthy in 1999, and continued by Amar in 2003, and most recently by Trent and Wick in 2009. In dimension $n=1$ we prove the corona theorem for the kernel multiplier algebras of Besov-Sobolev Banach spaces in the unit disk, extending the result for Hilbert spaces $H^\infty\cap Q_p$ by A. Nicolau and J. Xiao.

math.CA↗
arXiv2017

Two weight Commutators in the Dirichlet and Neumann Laplacian settings

In this paper we establish the characterization of the weighted BMO via two weight commutators in the settings of the Neumann Laplacian $Δ_{N_+}$ on the upper half space $\mathbb{R}^n_+$ and the reflection Neumann Laplacian $Δ_N$ on $\mathbb{R}^n$ with respect to the weights associated to $Δ_{N_+}$ and $Δ_{N}$ respectively. This in turn yields a weak factorization for the corresponding weighted Hardy spaces, where in particular, the weighted class associated to $Δ_{N}$ is strictly larger than the Muckenhoupt weighted class and contains non-doubling weights. In our study, we also make contributions to the classical Muckenhoupt--Wheeden weighted Hardy space (BMO space respectively) by showing that it can be characterized via area function (Carleson measure respectively) involving the semigroup generated by the Laplacian on $\mathbb{R}^n$ and that the duality of these weighted Hardy and BMO spaces holds for Muckenhoupt $A^p$ weights with $p\in (1,2]$ while the previously known related results cover only $p\in (1,{n+1\over n}]$. We also point out that this two weight commutator theorem might not be true in the setting of general operators $L$, and in particular we show that it is not true when $L$ is the Dirichlet Laplacian $Δ_{D_+}$ on $\mathbb{R}^n_+$.

math.AP↗
arXiv2017

Product Hardy, BMO spaces and iterated commutators associated with Bessel Schrödinger operators

In this paper we establish the product Hardy spaces associated with the Bessel Schrödinger operator introduced by Muckenhoupt and Stein, and provide equivalent characterizations in terms of the Bessel Riesz transforms, non-tangential and radial maximal functions, and Littlewood--Paley theory, which are consistent with the classical product Hardy space theory developed by Chang and Fefferman. Moreover, in this specific setting, we also provide another characterization via the Telyakovskií transform, which further implies that the product Hardy space associated with this Bessel Schrödinger operator is isomorphic to the subspace of suitable "odd functions" in the standard Chang--Fefferman product Hardy space. Based on the characterizations of these product Hardy spaces, we study the boundedness of the iterated commutator of the Bessel Riesz transforms and functions in the product BMO space associated with Bessel Schrödinger operator. We show that this iterated commutator is bounded above, but does not have a lower bound.

math.CA↗
arXiv2017

Characterizations of $H^1_{Δ_N}(\mathbb{R}^n)$ and $\rm BMO_{Δ_N}(\mathbb{R}^n)$ via Weak Factorizations and Commutators

This paper provides a deeper study of the Hardy and $\rm BMO$ spaces associated to the Neumann Laplacian $Δ_N$. For the Hardy space $H^1_{Δ_N}(\mathbb{R}^n)$ (which is a proper subspace of the classical Hardy space $H^1(\mathbb{R}^n)$) we demonstrate that the space has equivalent norms in terms of Riesz transforms, maximal functions, atomic decompositions, and weak factorizations. While for the space ${\rm BMO}_{Δ_N}(\mathbb{R}^n)$ (which contains the classical $\rm BMO(\mathbb{R}^n)$) we prove that it can be characterized in terms of the action of the Riesz transforms associated to the Neumann Laplacian on $L^\infty(\mathbb{R}^n)$ functions and in terms of the behavior of the commutator with the Riesz transforms. The results obtained extend many of the fundamental results known for $H^1(\mathbb{R}^n)$ and $\rm BMO(\mathbb{R}^n)$.

math.CA↗
arXiv2016

Lower bounds for the dyadic Hilbert transform

In this paper, we seek lower bounds of the dyadic Hilbert transform (Haar shift) of the form $\left\Vert S f\right\Vert_{L^2(K)}\geq C(I,K)\left\Vert f\right\Vert_{L^2(I)}$ where $I$ and $K$ are two dyadic intervals and $f$ supported in $I$. If $I\subset K$ such bound exist while in the other cases $K\subsetneq I$ and $K\cap I=\emptyset$ such bounds are only available under additional constraints on the derivative of $f$. In the later case, we establish a bound of the form $\left\Vert S f\right\Vert_{L^2(K)}\geq C(I,K)|\left\langle f\right\rangle_I|$ where $\left\langle f\right\rangle_I$ is the mean of $f$ over $I$. This sheds new light on the similar problem for the usual Hilbert transform that we exploit.

math.CA↗
arXiv2016

Two weight estimates with matrix measures for well localized operators

In this paper, we give necessary and sufficient conditions for weighted $L^2$ estimates with matrix-valued measures of well localized operators. Namely, we seek estimates of the form: \[ \| T(\mathbf{W} f)\|_{L^2(\mathbf{V})} \le C\|f\|_{L^2(\mathbf{W})} \] where $T$ is formally an integral operator with additional structure, $\mathbf{W}, \mathbf{V}$ are matrix measures, and the underlying measure space possesses a filtration. The characterization we obtain is of Sawyer-type; in particular we show that certain natural testing conditions obtained by studying the operator and its adjoint on indicator functions suffice to determine boundedness. Working in both the matrix weighted setting and the setting of measure spaces with arbitrary filtrations requires novel modifications of a T1 proof strategy; a particular benefit of this level of generality is that we obtain polynomial estimates on the complexity of certain Haar shift operators.

math.FA↗
arXiv2016

Bergman projection induced by kernel with integral representation

Bounded Bergman projections $P_ω:L^p_ω(v)\to L^p_ω(v)$, induced by reproducing kernels admitting the representation $$ \frac{1}{(1-\overline{z}ζ)^γ}\int_0^1\frac{dν(r)}{1-r\overline{z}ζ}, $$ and the corresponding (1,1)-inequality are characterized in terms of Bekollé-Bonami-type conditions. The two-weight inequality for the maximal Bergman projection $P^+_ω:L^p_ω(u)\to L^p_ω(v)$ in terms of Sawyer-testing conditions is also discussed.

math.CV↗
arXiv2016

Characterizations of product Hardy spaces in Bessel setting

In this paper, we work in the setting of Bessel operators and Bessel Laplace equations studied by Weinstein, Huber, and the harmonic function theory in this setting introduced by Muckenhoupt--Stein, especially the generalised Cauchy--Riemann equations and the conjugate harmonic functions. We provide the equivalent characterizations of product Hardy spaces associated with Bessel operators in terms of the Bessel Riesz transforms, non-tangential and radial maximal functions defined via Poisson and heat semigroups, based on the atomic decomposition, the extension of Merryfield's result which connects the product non-tangential maximal function and area function, and on the grand maximal function technique which connects the product non-tangential and radial maximal function. We then obtain directly the decomposition of the product BMO space associated with Bessel operators. These results are a first extension for product Hardy and BMO associated to a differential operator other than the Laplacian and are a major step beyond the Chang--Fefferman setting.

math.AP↗
arXiv2016

Two Weight Inequalities for Riesz Transforms: Uniformly Full Dimension Weights

Fix an integer $ n$ and number $d$, $ 0< d\neq n-1 \leq n$, and two weights $ w$ and $ σ$ on $ \mathbb R ^{n}$. We two extra conditions (1) no common point masses and (2) the two weights separately are not concentrated on a set of codimension one, uniformly over locations and scales. (This condition holds for doubling weights.) Then, we characterize the two weight inequality for the $ d$-dimensional Riesz transform on $ \mathbb R ^{n}$, \begin{equation*} \sup_{0< a < b < \infty}\left\lVert \int_{a < \lvert x-y\rvert < b} f (y) \frac {x-y} {\lvert x-y\rvert ^{d+1}} \; σ(dy) \right\rVert_{L ^{2} (\mathbb{R}^n;w)} \le \mathscr N \lVert f\rVert_{L ^2 (\mathbb{R}^n;σ)} \end{equation*} in terms of these two conditions, and their duals: For finite constants $ \mathscr A_2$ and $ \mathscr T$, uniformly over all cubes $ Q\subset \mathbb R ^{n}$ \begin{gather*} \frac {w (Q)} {\lvert Q\rvert ^{d/n}} \int_{\mathbb R ^{n}} \frac {\lvert Q\rvert ^{d/n}} {\lvert Q\rvert ^{2d/n} +{dist}(x, Q) ^{2d/n}} \; σ(dx) \leq \mathscr A_2 \\ \int_{Q} \lvert \mathsf R_σ \mathbf 1_{Q} (x)\rvert ^2 \; w(dx) \le \mathscr T ^2 σ(Q), \end{gather*} where $ \mathsf R_σ$ denotes any of the truncations of the Riesz transform as above, the dual conditions are obtained by interchanging the roles of the two weights. Examples show that a key step of the proof fails in absence of the extra geometric condition imposed on the weights.

math.CA↗
arXiv2016

A remark on the multipliers on spaces of weak products of functions

If $\mathcal{H}$ denotes a Hilbert space of analytic functions on a region $Ω\subseteq \mathbb{C}^d$, then the weak product is defined by $$\mathcal{H}\odot\mathcal{H}=\left\{h=\sum_{n=1}^\infty f_n g_n : \sum_{n=1}^\infty \|f_n\|_{\mathcal{H}}\|g_n\|_{\mathcal{H}} <\infty\right\}.$$ We prove that if $\mathcal{H}$ is a first order holomorphic Besov Hilbert space on the unit ball of $\mathbb{C}^d$, then the multiplier algebras of $\mathcal{H}$ and of $\mathcal{H}\odot\mathcal{H}$ coincide.

math.CV↗
arXiv2016

Commutators in the Two-Weight Setting

Let $R$ be the vector of Riesz transforms on $\mathbb{R}^n$, and let $μ,λ\in A_p$ be two weights on $\mathbb{R}^n$, $1 < p < \infty$. The two-weight norm inequality for the commutator $[b, R] : L^p(\mathbb{R}^n;μ) \to L^p(\mathbb{R}^n;λ)$ is shown to be equivalent to the function $b$ being in a BMO space adapted to $μ$ and $λ$. This is a common extension of a result of Coifman-Rochberg-Weiss in the case of both $λ$ and $μ$ being Lebesgue measure, and Bloom in the case of dimension one.

math.CA↗