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Evgueni Doubtsov

Publications and source records attributed to Evgueni Doubtsov.

At least 19 recordsLinked to original sources
arXiv2026

Square function characterization of Hardy-type spaces

The well-known characterization of Hardy spaces $\mathrm{H}_{p}(\mathbb D)$, $0 < p < \infty$, in terms of the Littlewood-Paley g-function $$ S f (\zeta) = \left(\int_0^1 |f' (r \zeta)|^2 (1 - r) \mathrm dr\right)^{1/2} \in \mathrm{L}_{p} $$ is generalized to Hardy-type spaces $X_A$ corresponding to quasi-Banach lattices $X$ on the unit circle $\mathbb T$ under the assumption that the Hardy-Littlewood maximal operator $M$ is bounded in $(X^\delta)'$ with some $\delta > 0$. As an application to composition operators $C_\varphi$, we derive an exact criterion for the boundedness and compactness of $C_\varphi : \mathcal{B}^\omega \to X_A$, where $\mathcal{B}^\omega = \{f \mid \sup |f'|/\omega < \infty\}$ is the weighted Bloch space with a log-convex radial weight $\omega$, generalizing recent results in the one-dimensional setting.

math.FA↗
arXiv2026

Composition operators between de Branges-Rovnyak and Hardy spaces

Let $d\ge 1$ and $\varphi: B_d\to\mathbb{D}$ be a holomorphic function, where $B_d$ denotes the open unit ball of $\mathbb{C}^d$ and $\mathbb{D} = B_1$. Let $b: \mathbb{D} \to \mathbb{D}$ be a holomorphic function and $\mathcal {H}(b)$ denote the corresponding de Branges-Rovnyak space. We show that compactness of the composition operator $C_\varphi$ from $\mathcal{H}(b)$ to the Hardy space $H^2(B_d)$ is related to natural restrictions on the Nevanlinna counting functions of the slice-functions $\varphi_\zeta$, $\zeta\in \partial B_d$.

math.CV↗
arXiv2026

Composition operators between model and Hardy spaces

Let $n\ge 1$ and $\varphi: \mathbb{D}^n\to\mathbb{D}$ be a holomorphic function, where $\mathbb{D}$ denotes the open unit disk of $\mathbb{C}$. Let $\Theta: \mathbb{D} \to \mathbb{D}$ be an inner function and $K^p_\Theta$, $p>0$, denote the corresponding model space. We obtain characterizations of the compact composition operators $C_\varphi: K^p_\Theta \to H^p(\mathbb{D}^n)$, $1<p<\infty$, where $H^p(\mathbb{D}^n)$ denotes the Hardy space.

math.CV↗
arXiv2026

Weighted Chui's conjecture

The goals of this paper are threefold. First, we show that a counterpart of the Newman bound related to the Chui conjecture is valid in the case where the gradient of Coulomb potential is generated by arbitrary positive charges placed at the boundary of a unit ball. Second, we prove that our bound is sharp in the two-dimensional case. Finally, we discuss a related problem, where the unit charges are placed in the unit disc.

math.CA↗
arXiv2024

Reverse Carleson measures for spaces of analytic functions

Let $X$ be a quasi-Banach space of analytic functions in the unit disc and let $q>0$. A finite positive Borel measure $\mu$ in the closed unit disc $\overline{\mathbb{D}}$ is called a $q$-reverse Carleson measure for $X$ if and only if there exists a constant $C>0$ such that $$\|f\|_{X}\leq C \|f\|_{L^q(\overline{\mathbb D},d\mu)} $$ for all $f\in X\cap C(\overline{\mathbb D})$. We fully characterize the $q$-reverse Carleson measures with all $q>0$ for Hardy spaces $H^p(\mathbb D)$ with all $0<p\leq \infty$, for the space $\mathrm{BMOA}(\mathbb D)$ and for the Bloch space. In addition, we describe $q$-reverse Carleson measures for the holomorphic Triebel--Lizorkin spaces $HF_0^{q,r}$ and the holomorphic Besov spaces $HB_0^{q,r}$. Related results are obtained for the Hardy spaces and certain holomorphic Triebel--Lizorkin spaces in the unit ball of $\mathbb{C}^d$.

math.CV↗
arXiv2024

A characterization of Calder\'on-Zygmund operators on RBMO

Let $\mathrm{RBMO}(\mu) = \mathrm{RBMO}(\mathbb{R}^m, \mu)$ denote the regular BMO space introduced by X. Tolsa for an $n$-dimensional finite positive measure on $\mathbb{R}^m$, $0<n \le m$. We characterize the bounded Calder\'on-Zygmund operators $T:\mathrm{RBMO}(\mu) \to \mathrm{RBMO}(\mu)$ in terms of the function $T1$.

math.FA↗
arXiv2024

Compact linear combinations of composition operators on Hardy spaces

Let $\varphi_j$, $j=1,2, \dots, N$, be holomorphic self-maps of the unit disk $\mathbb{D}$ of $\mathbb{C}$. We prove that the compactness of a linear combination of the composition operators $C_{\varphi_j}: f\mapsto f\circ\varphi_j$ on the Hardy space $H^p(\mathbb{D})$ does not depend on $p$ for $0<p<\infty$. This answers a conjecture of Choe et al. about the compact differences $C_{\varphi_1} - C_{\varphi_2}$ on $H^p(\mathbb{D})$, $0<p<\infty$.

math.CV↗
arXiv2024

Compact composition operators on model spaces

Let $\varphi: B_d\to\mathbb{D}$, $d\ge 1$, be a holomorphic function, where $B_d$ denotes the open unit ball of $\mathbb{C}^d$ and $\mathbb{D}= B_1$. Let $\Theta: \mathbb{D} \to \mathbb{D}$ be an inner function and let $K^p_\Theta$ denote the corresponding model space. For $p>1$, we characterize the compact composition operators $C_\varphi: K^p_\Theta \to H^p(B_d)$, where $H^p(B_d)$ denotes the Hardy space.

math.CV↗
arXiv2024

Mutual singularity of Riesz products on the unit sphere

We prove analogs of Peyri\`ere's mutual singularity theorem for standard and generalized Riesz products on the unit sphere of $\mathbb{C}^n$, $n\ge 2$. As a corollary, we obtain an analog of Zygmund's dichotomy for the Riesz products under consideration.

math.CV↗
arXiv2023

Reverse Carleson measures for Hardy spaces in the unit ball

Let $H^p=H^p(B_d)$ denote the Hardy space in the open unit ball $B_d$ of $\mathbb{C}^d$, $d\ge 1$. We characterize the reverse Carleson measures for $H^p$, $1 0$. Given a non-inner holomorphic function $b: B_d \to B_1$, we obtain properties of the reverse Carleson measures for the de Branges-Rovnyak space $\mathcal{H}(b)$.

math.CV↗
arXiv2023

Dominant sets for model spaces in several variables

Let $I$ be an inner function in $\mathcal{D} = B_{n_1}\times B_{n_2}\cdots \times B_{n_k}$, where $B_n$ denotes the open unit ball of $\mathbb{C}^n$, $n\ge 1$. We construct dominant sets for the space $H^2 \ominus I H^2$, where $H^2 = H^2(\mathcal{D})$ denotes the standard Hardy space.

math.CV↗
arXiv2022

A T(P) theorem for Zygmund spaces on domains

Let $D\subset \mathbb{R}^d$ be a bounded Lipschitz domain, $\omega$ be a high order modulus of continuity and let $T$ be a convolution Calder\'{o}n-Zygmund operator. We characterize the bounded restricted operators $T_D$ on the Zygmund space $\mathcal{C}_{\omega}(D)$. The characterization is based on properties of $T_D P$ for appropriate polynomials $P$ restricted to $D$.

math.FA↗
arXiv2021

Calder\'on-Zygmund operators on RBMO

Let $\mu$ be an $n$-dimensional finite positive measure on $\mathbb{R}^m$. We obtain a $T1$ condition sufficient for the boundedness of Calder\'{o}n-Zygmund operators on $\textrm{RBMO}(\mu)$, the regular BMO space of Tolsa.

math.CA↗
arXiv2020

Clark measures and de Branges-Rovnyak spaces in several variables

Let $B_n$ denote the unit ball of $\mathbb{C}^n$, $n\ge 1$, and let $\mathcal{D}$ denote a finite product of $B_{n_j}$, $j\ge 1$. Given a non-constant holomorphic function $b: \mathcal{D} \to B_1$, we study the corresponding family $\sigma_\alpha[b]$, $\alpha\in\partial B_1$, of Clark measures on the distinguished boundary $\partial\mathcal{D}$. We construct a natural unitary operator from the de Branges-Rovnyak space $\mathcal{H}(b)$ onto the Hardy space $H^2(\sigma_\alpha)$. As an application, for $\mathcal{D}= B_n$ and an inner function $I: B_n \to B_1$, we show that the property $\sigma_1[I]\ll\sigma_1[b]$ is directly related to the membership of an appropriate explicit function in $\mathcal{H}(b)$.

math.CV↗
arXiv2019

Clark measures on the torus

Let $\mathbb{D}$ denote the unit disc of $\mathbb{C}$ and let $\mathbb{T}= \partial\mathbb{D}$. Given a holomorphic function $\varphi: \mathbb{D}^n \to \mathbb{D}$, $n\ge 2$, we study the corresponding family $\sigma_\alpha[\varphi]$, $\alpha\in\mathbb{T}$, of Clark measures on the torus $\mathbb{T}^n$. If $\varphi$ is an inner function, then we introduce and investigate related isometric operators $T_\alpha$ mapping analogs of model spaces into $L^2(\sigma_\alpha)$, $\alpha\in\mathbb{T}$.

math.CV↗
arXiv2019

Clark measures on the complex sphere

Let $B_d$ denote the unit ball of $\mathbb{C}^d$, $d\ge 1$. Given a holomorphic function $\varphi: B_d \to B_1$, we study the corresponding family $\sigma_\alpha[\varphi]$, $\alpha\in\partial B_1$, of Clark measures on the unit sphere $\partial B_d$. If $\varphi$ is an inner function, then we introduce and investigate related unitary operators $U_\alpha$ mapping analogs of model spaces onto $L^2(\sigma_\alpha)$, $\alpha\in\partial B_1$. In particular, we explicitly characterize the set of $U_\alpha^* f$ such that $f\sigma_\alpha$ is a pluriharmonic measure. Also, for an arbitrary holomorphic $\varphi: B_d \to B_1$, we use the family $\sigma_\alpha[\varphi]$ to compute the essential norm of the composition operator $C_\varphi: H^2(B_1)\to H^2(B_d)$.

math.CV↗
arXiv2019

Factorization by elementary matrices, null-homotopy and products of exponentials for invertible matrices over rings

Let $R$ be a commutative unital ring. A well-known factorization problem is whether any matrix in $\mathrm{SL}_n(R)$ is a product of elementary matrices with entries in $R$. To solve the problem, we use two approaches based on the notion of the Bass stable rank and on construction of a null-homotopy. Special attention is given to the case, where $R$ is a ring or Banach algebra of holomorphic functions. Also, we consider a related problem on representation of a matrix in $\mathrm{GL}_n(R)$ as a product of exponentials.

math.AC↗