Dmitry Yakubovich
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Previous Organizations / Institutes
The organizations / institutes from the scholar's other articles in the past ten years
Research Subjects
Dmitry Yakubovich has a total of 37 co-authors. Here are the top co-authors by number of shared publications:
- Michael A. Dritschel
Newcastle University
6 shared publications - Anton Baranov
Saint Petersburg State University
5 shared publications - Daniel Estévez
Oceano Atlantico 38, Tres Cantos, Madrid, Spain
5 shared publications - José Manuel Rodríguez
Departamento de Matemáticas, Universidad Carlos III de Madrid, Leganés, Spain
4 shared publications - Eva Gallardo-Gutiérrez
Facultad de CC Matemáticas Universidad Complutense de Madrid and Instituto de Ciencias Matemáticas ICMAT, Dpto. de Análisis Matemático y Matemática Aplicada Madrid Spain
3 shared publications - Glenier Bello
Departamento de Matemáticas, Universidad Autónoma de Madrid, Madrid, Spain
3 shared publications
Latest Publications
- 25 October 2026
- Published by Springer Nature in Journal d'Analyse Mathématique
- p. 1-31
Operators with small Kreiss constants
- 25 October 2026
- Published by Springer Nature in Journal d'Analyse Mathématique
- p. 1-31
Operators with small Kreiss constants
- Open Access
- 17 February 2026
- Published by Springer Nature in Results in Mathematics
- Vol. 81 (2) , 50
Self-improving Estimates of Growth of Subharmonic and Analytic Functions
Given a bounded open subset $$\Omega $$ and closed subsets A , B of $$\mathbb {R}^k$$ , we discuss when an estimate $$u(x)\le g(\operatorname {dist}(x,A\cup B))$$ , $$x\in \Omega \setminus (A\cup B)$$ , for a function u subharmonic on $$\Omega \setminus B$$ , implies that $$u(x)\le h(\operatorname {dist}(x,B))$$ , $$x\in \Omega \setminus B$$ , where $$g,h:(0,\infty )\rightarrow (0,\infty )$$ are decreasing functions and $$g(0^+)=h(0^+)=\infty $$ . We seek for explicit expressions of h in terms of g . We give some results of this type and show that Domar’s work Domar, Y Ark. Mat. 3, 429–440 (1957) permits one to deduce other results in this direction. Then we compare these two approaches. Similar results are deduced for estimates of analytic functions.- 17 February 2026
- Published by Springer Nature in Results in Mathematics
- Vol. 81 (2) , 50
Open AccessSelf-improving Estimates of Growth of Subharmonic and Analytic Functions
Given a bounded open subset $$\Omega $$ and closed subsets A , B of $$\mathbb {R}^k$$ , we discuss when an estimate $$u(x)\le g(\operatorname {dist}(x,A\cup B))$$ , $$x\in \Omega \setminus (A\cup B)$$ , for a function u subharmonic on $$\Omega \setminus B$$ , implies that $$u(x)\le h(\operatorname {dist}(x,B))$$ , $$x\in \Omega \setminus B$$ , where $$g,h:(0,\infty )\rightarrow (0,\infty )$$ are decreasing functions and $$g(0^+)=h(0^+)=\infty $$ . We seek for explicit expressions of h in terms of g . We give some results of this type and show that Domar’s work Domar, Y Ark. Mat. 3, 429–440 (1957) permits one to deduce other results in this direction. Then we compare these two approaches. Similar results are deduced for estimates of analytic functions. - Open Access
Embedding of Toeplitz operators with smooth symbols into strongly continuous semigroups
Using the model theory for Toeplitz operators with smooth symbols developed by the fourth author in the 80’s, we study whether such operators T_F can be embedded into a C_0 -semigroup of operators on the Hardy space Hp of the open unit disk, 1 < p < ∞. We show that it is the case as soon as 0 belongs to the unbounded connected component of C minus the interior of the spectrum of T_F . We provide several conditions on the symbol F, both geometric and analytic in nature, ensuring that this sufficient condition is also necessary. For a certain class of symbols, where the curve F (T) is a “figure eight in a loop” such that C \ σ(T_F ) has a bounded connected component, we obtain a complete characterization of the embeddability of T_F into a C_0 -semigroup. In the last part of the paper, we discuss the embeddability of T_F when the symbol F is not necessarily smooth, using connections with the numerical range and the functional calculus for bounded sectorial operators.
Open AccessEmbedding of Toeplitz operators with smooth symbols into strongly continuous semigroups
Using the model theory for Toeplitz operators with smooth symbols developed by the fourth author in the 80’s, we study whether such operators T_F can be embedded into a C_0 -semigroup of operators on the Hardy space Hp of the open unit disk, 1 < p < ∞. We show that it is the case as soon as 0 belongs to the unbounded connected component of C minus the interior of the spectrum of T_F . We provide several conditions on the symbol F, both geometric and analytic in nature, ensuring that this sufficient condition is also necessary. For a certain class of symbols, where the curve F (T) is a “figure eight in a loop” such that C \ σ(T_F ) has a bounded connected component, we obtain a complete characterization of the embeddability of T_F into a C_0 -semigroup. In the last part of the paper, we discuss the embeddability of T_F when the symbol F is not necessarily smooth, using connections with the numerical range and the functional calculus for bounded sectorial operators.
- Open Access
Embedding of Toeplitz operators with smooth symbols into strongly continuous semigroups
Using the model theory for Toeplitz operators with smooth symbols developed by the fourth author in the 80's, we study whether such operators $T_{F}$ can be embedded into a $C_{0}$-semigroup of operators on the Hardy space $H^p$ of the open unit disk, $1<p<\infty$. We show that it is the case as soon as $0$ belongs to the unbounded connected component of $\mathbb{C}$ minus the interior of the spectrum of $T_{F}$. We provide several conditions on the symbol $F$, both geometric and analytic in nature, ensuring that this sufficient condition is also necessary. For a certain class of symbols, where the curve $F(\mathbb{T})$ is a ``figure eight in a loop" such that $\mathbb{C}\setminusσ(T_F)$ has a bounded connected component, we obtain a complete characterization of the embeddability of $T_F$ into a $C_0$-semigroup. In the last part of the paper, we discuss the embeddability of $T_F$ when the symbol $F$ is not necessarily smooth, using connections with the numerical range and the functional calculus for bounded sectorial operators.Open AccessEmbedding of Toeplitz operators with smooth symbols into strongly continuous semigroups
Using the model theory for Toeplitz operators with smooth symbols developed by the fourth author in the 80's, we study whether such operators $T_{F}$ can be embedded into a $C_{0}$-semigroup of operators on the Hardy space $H^p$ of the open unit disk, $1<p<\infty$. We show that it is the case as soon as $0$ belongs to the unbounded connected component of $\mathbb{C}$ minus the interior of the spectrum of $T_{F}$. We provide several conditions on the symbol $F$, both geometric and analytic in nature, ensuring that this sufficient condition is also necessary. For a certain class of symbols, where the curve $F(\mathbb{T})$ is a ``figure eight in a loop" such that $\mathbb{C}\setminusσ(T_F)$ has a bounded connected component, we obtain a complete characterization of the embeddability of $T_F$ into a $C_0$-semigroup. In the last part of the paper, we discuss the embeddability of $T_F$ when the symbol $F$ is not necessarily smooth, using connections with the numerical range and the functional calculus for bounded sectorial operators. - 21 October 2025
- Published by European Mathematical Society - EMS - Publishing House GmbH in Journal of the European Mathematical Society
Complete frequencies for Koenigs domains
We provide a complete characterization of those non-elliptic semigroups of holomorphic self-maps of the unit disc for which the linear span of eigenvectors of the generator of the corresponding semigroup of composition operators is weak-star dense in H^{\infty} . We also give some necessary and some sufficient conditions for completeness in H^{p} . This problem is equivalent to the completeness of the corresponding exponential functions in H^{\infty} (in the weak-star sense) or in H^{p} of the Koenigs domain of the semigroup. As a tool needed for the results, we introduce and study discontinuities of semigroups of holomorphic self-maps of the unit disc.
- 21 October 2025
- Published by European Mathematical Society - EMS - Publishing House GmbH in Journal of the European Mathematical Society
Complete frequencies for Koenigs domains
We provide a complete characterization of those non-elliptic semigroups of holomorphic self-maps of the unit disc for which the linear span of eigenvectors of the generator of the corresponding semigroup of composition operators is weak-star dense in H^{\infty} . We also give some necessary and some sufficient conditions for completeness in H^{p} . This problem is equivalent to the completeness of the corresponding exponential functions in H^{\infty} (in the weak-star sense) or in H^{p} of the Koenigs domain of the semigroup. As a tool needed for the results, we introduce and study discontinuities of semigroups of holomorphic self-maps of the unit disc.
- Open Access
Self-improving estimates of growth of subharmonic and analytic functions
Given a bounded open subset $\Omega$ and closed subsets $A,B$ of $\mathbb{R}^k$, we discuss when an estimate $u(x)\le g(dist(x,A\cup B))$, $x\in\Omega\setminus(A\cup B)$, for a function $u$ subharmonic on $\Omega\setminus B$, implies that $u(x)\le h(dist(x,B))$, $x\in\Omega\setminus B$, where $g,h:(0,\infty)\to (0,\infty)$ are decreasing functions and $g(0^+)=h(0^+)=\infty$. We seek for explicit expressions of $h$ in terms of $g$. We give some results of this type and show that Domar's work (On the existence of a largest subharmonic minorant of a given function, Ark. Mat., 3 (1957), pp. 429-440) permits one to deduce other results in this direction. Then we compare these two approaches. Similar results are deduced for estimates of analytic functions.Open AccessSelf-improving estimates of growth of subharmonic and analytic functions
Given a bounded open subset $\Omega$ and closed subsets $A,B$ of $\mathbb{R}^k$, we discuss when an estimate $u(x)\le g(dist(x,A\cup B))$, $x\in\Omega\setminus(A\cup B)$, for a function $u$ subharmonic on $\Omega\setminus B$, implies that $u(x)\le h(dist(x,B))$, $x\in\Omega\setminus B$, where $g,h:(0,\infty)\to (0,\infty)$ are decreasing functions and $g(0^+)=h(0^+)=\infty$. We seek for explicit expressions of $h$ in terms of $g$. We give some results of this type and show that Domar's work (On the existence of a largest subharmonic minorant of a given function, Ark. Mat., 3 (1957), pp. 429-440) permits one to deduce other results in this direction. Then we compare these two approaches. Similar results are deduced for estimates of analytic functions. - 22 September 2023
- Published by Springer Nature
- p. 61-71
On the Work by Serguei Naboko on the Similarity to Unitary and Selfadjoint Operators
- 22 September 2023
- Published by Springer Nature
- p. 61-71
On the Work by Serguei Naboko on the Similarity to Unitary and Selfadjoint Operators
- 17 November 2022
- Published by Springer Nature in Israel Journal of Mathematics
- Vol. 255 (1) , 63-80
Generators of C0-semigroups of weighted composition operators
- 17 November 2022
- Published by Springer Nature in Israel Journal of Mathematics
- Vol. 255 (1) , 63-80
Generators of C0-semigroups of weighted composition operators
- Open Access
An operator model in the annulus
For an invertible linear operator $T$ on a Hilbert space $H$, put \[ \alpha(T^*,T) := -T^{*2}T^2 + (1+r^2) T^* T - r^2 I, \] where $I$ stands for the identity operator on $H$ and $r\in (0,1)$; this expression comes from applying Agler's hereditary functional calculus to the polynomial $\alpha(t)=(1-t) (t-r^2)$. We give a concrete unitarily equivalent functional model for operators satisfying $\alpha(T^*,T)\ge0$. In particular, we prove that the closed annulus $r\le |z|\le 1$ is a complete $K$-spectral set for $T$. We explain the relation of the model with the Sz.-Nagy--Foias one and with the observability gramian and discuss the relationship of this class with other operator classes related to the annulus.Open AccessAn operator model in the annulus
For an invertible linear operator $T$ on a Hilbert space $H$, put \[ \alpha(T^*,T) := -T^{*2}T^2 + (1+r^2) T^* T - r^2 I, \] where $I$ stands for the identity operator on $H$ and $r\in (0,1)$; this expression comes from applying Agler's hereditary functional calculus to the polynomial $\alpha(t)=(1-t) (t-r^2)$. We give a concrete unitarily equivalent functional model for operators satisfying $\alpha(T^*,T)\ge0$. In particular, we prove that the closed annulus $r\le |z|\le 1$ is a complete $K$-spectral set for $T$. We explain the relation of the model with the Sz.-Nagy--Foias one and with the observability gramian and discuss the relationship of this class with other operator classes related to the annulus. - 26 January 2021
- Published by Springer Nature in Banach Journal of Mathematical Analysis
- Vol. 15 (2) , 1-29
Functional models up to similarity and a-contractions
- 26 January 2021
- Published by Springer Nature in Banach Journal of Mathematical Analysis
- Vol. 15 (2) , 1-29
Functional models up to similarity and a-contractions