Sameer Chavan, Rajeev Gupta, Md. Ramiz Reza
We obtain a formula that relates the spherical moments of the multiplication tuple on a Dirichlet-type space to a complex moment problem in several variables. This can be seen as the ball-analogue of a formula originally invented by Richter. We capitalize on this formula to study Dirichlet-type spaces on the unit ball and joint $2$-isometries.
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In the context of a theorem of Richter, we establish a similarity between $C_0$-semigroups of analytic 2-isometries $\{T(t)\}_{t\geq0}$ acting on a Hilbert space $\mathcal H$ and the multiplication operator semigroup $\{M_{ϕ_t}\}_{t\geq 0}$ induced by $ϕ_t(s)=\exp (-st)$ for $s$ in the right-half plane $\mathbb{C}_+$ acting boundedly on weighted Dirichlet spaces on $\mathbb{C}_+$. As a consequence, we derive a connection with the right shift semigroup $\{S_t\}_{t\geq 0}$ $$ S_tf(x)=\left \{ \begin{array}{ll} 0 & \mbox { if }0\leq t\leq x, \\ f(x-t)& \mbox { if } x>t, \end{array} \right . $$ ac…
We consider cyclic $m$-isometries on a complex separable Hilbert space. Such operators are characterized in terms of shifts on abstract spaces of weighted Dirichlet type. Our results resemble those of Agler and Stankus, but our model spaces are described in terms of Dirichlet integrals rather than analytic Dirichlet operators. The chosen point of view allows us to construct a variety of examples. An interesting feature among all of these is that the corresponding model spaces are contained in a certain subspace of the Hardy space $H^2$, depending only on the order of the corresponding operator…
In this article, we study the geometry of an infinite dimensional Hyperbolic space. We will consider the group of isometries of the Hilbert ball equipped with the Carath$\acute{e}$odory metric and learn about some special subclasses of this group. We will also find some unitary equivalence condition and compute some cardinalities.
Corresponding to any $(m-1)$-tuple of semi-spectral measures on the unit circle, a weighted Dirichlet-type space is introduced and studied. We prove that the operator of multiplication by the coordinate function on these weighted Dirichlet-type spaces acts as an analytic $m$-isometry and satisfies a certain set of operator inequalities. Moreover, it is shown that an analytic $m$-isometry which satisfies this set of operator inequalities can be represented as an operator of multiplication by the coordinate function on a weighted Dirichlet-type space induced from an $(m-1)$-tuple of semi-spectra…
Higher order weighted Dirichlet type spaces with poly-superharmonic weights and Dirichlet type operators of finite order
本文研究了与多项超调和权重相关的一类单位圆上高阶加权狄利克雷型空间，通过建立高阶Littlewood-Paley公式，将权重的迭代拉普拉斯算子与移位算子的高阶缺陷算子联系起来，引入了有限阶狄利克雷型算子，扩展了循环完全超膨胀和完全超收缩算子及m-等距算子的模型理论。
We characterize polynomials that are cyclic in Dirichlet-type spaces in the unit ball in $\mathbb C^2$
We characterize model polynomials that are cyclic in Dirichlet-type spaces in the unit ball of $\mathbb{C}^n$, and we give a sufficient capacity condition in order to identify non-cyclic vectors.
We extend results of Bénéteau, Condori, Liaw, Seco, and the author concerning cyclic vectors in Dirichlet-type spaces to the setting of the unit ball, identifying some classes of cyclic and non-cyclic functions, and noting the necessity of certain capacity conditions.
The forms of surjective multiplicative isometries from the Smirnov class on the ball and the polydisk are given.
Extreme points of the unit balls and isometries of noncommutative quasi-Banach Marcinkiewicz spaces
本文刻画了Marcinkiewicz空间单位球的极值点，证明非交换情形下正等距为初等形式，并研究了弱$L_p$空间等上的等距及其单参数群。
Dirichlet-type spaces of the bidisc and Toral $2$-isometries
本研究引入单位双圆盘上的Dirichlet型空间，证明其乘子、多项式稠密等性质，求解Gleason问题，刻画交换乘法对的toral 2-等距与Cowen-Douglas类属性，提出游荡子空间概念并建立循环解析2-等距的双圆盘表示定理。
Examples of critically cyclic functions in the Dirichlet spaces of the ball
本文通过构造例子，研究了球体上Dirichlet空间中临界循环函数的性质，揭示了循环性与指数α之间的关系。
We examine the group of isometries of the open unit ball of a complex Banach space of certain bounded linear operators equipped with the Carathéodory metric. Therein we obtain a charactrization of the normal isometries in terms of their special type of fixed points.
In Bergman and Dirichlet spaces, the shift operator is not an isometry, but it is a left invertible operator. In this paper we give conditions on the left invertible operators such that a operator version, in the sense of Rosenblum and Rovnyak, of the Wold decomposition to take place.
Wold-type decomposition for Doubly commuting two-isometries
本文研究希尔伯特空间上双交换2-等距的结构，证明其存在Wold型分解，且解析部分与双圆盘上Dirichlet型空间的坐标函数乘法对酉等价，丰富了算子理论的相关结果。
Isometries of James-Schreier and Lorentz spaces
本文通过极值点保持方法研究实 Banach 序列空间上的满射线性等距群，刻画了 James-Schreier 空间 $V_1$ 对偶单位球的极值点，证明其等距映射仅为 $\pm Id$，并给出 Lorentz 序列空间的 Banach-Stone 型结果。
Dirichlet Spaces In Balls And Half-spaces of $\R^n$
本文将经典二维圆盘中Douglas和Ahlfors对Dirichlet范数的刻画推广到球与$\R^n$半空间，给出了相应背景下Dirichlet范数的等价特征。
An improvement of the Blanco-Koldobsky-Turnšek characterization of isometries
本文通过引入水平向量概念，改进了Blanco-Koldobsky-Turnšek对等距映射的特征化，并在特定空间中进一步细化了该特征化。
We study bifurcation from a branch of trivial solutions of semilinear elliptic Dirichlet boundary value problems on a geodesic ball, whose radius is used as the bifurcation parameter. In the proof of our main theorem we obtain in addition a special case of an index theorem due to S. Smale.
In this paper we characterize surjective isometries on certain classes of non-commutative spaces associated with semi-finite von Neumann algebras: the Lorentz spaces $L^{w,1}$, as well as the spaces $L^1+L^\infty$ and $L^1\cap L^\infty$. The technique used in all three cases relies on characterizations of the extreme points of the unit balls of these spaces. Of particular interest is that the representations of isometries obtained in this paper are global representations.
In this paper, we investigate when weighted composition operators acting on Dirichlet spaces $\mathcal{D}(\mathbb{B}_{N})$ are complex symmetric with respect to some special conjugations, and provide some characterizations of Hermitian weighted composition operators on $\mathcal{D}(\mathbb{B}_{N})$. Furthermore, we give a sufficient and necessary condition for $J$-symmetric weighted composition operators on Hardy spaces $H^2(\mathbb{B}_{N})$ to be unitary or Hermitian, then some new examples of complex symmetric weighted composition operators on $H^2(\mathbb{B}_{N})$ are obtained. We also disc…
We prove that, if the closed unit ball of a normed space $X$ has sufficiently many extreme points, then every mapping $Φ$ from $X$ into itself with the following property is affine: For any pair of points in $X$, there exists a (not necessarily linear) surjective isometry on $X$ that coincides with $Φ$ at the two points. We also consider surjectivity of such a mapping in some special cases including C$^*$-algebras.
The classical Dirichlet space is a complete Pick space, hence by a theorem of Agler and McCarthy, there exists an embedding $b$ of the unit disc into a $d$-dimensional ball such that composition with $b$ realizes the Dirichlet space as a quotient of the Drury-Arveson space. We show that $d =\infty$ is necessary, even if we only demand that composition with $b$ induces a surjective map between the multiplier algebras.
This article gives a procedure to convert a frame which is not a tight frame into a Parseval frame for the same space, with the requirement that each element in the resulting Parseval frame can be explicitly written as a linear combination of the elements in the original frame. Several examples are considered, such as a Fourier frame on a spiral. The procedure can be applied to the construction of Parseval frames for L^2(B(0,R)), the space of square integrable functions whose domain is the ball of radius R. When a finite number of measurements are used to reconstruct a signal in L^2(B(0,R)), e…
On local preservation of orthogonality and its application to isometries
本研究探讨有限维巴拿赫空间上线性算子的Birkhoff-James正交性局部保持性，关联k-光滑性保持与单位球极值性质，改进了多面体巴拿赫空间上的Blanco-Koldobsky-Turnsek等距映射刻画结果。
The volume of the unit ball of the Lebesgue sequence space $\ell_p^m$ is very well known since the times of Dirichlet. We calculate the volume of the unit ball in the mixed norm $\ell^n_q(\ell_p^m)$, whose special cases are nowadays popular in machine learning under the name of group lasso. We consider the real as well as the complex case. The result is given by a closed formula involving the gamma function, only slightly more complicated than the one of Dirichlet. We close by an overview of open problems.
We show that the Dirichlet space is not a quotient of the Drury-Arveson space on the n-ball for any finite n. The proof is based a quantitative comparison of the metrics induced by the Hilbert spaces
We study pairs of Dirichlet forms related by an intertwining order isomorphisms between the associated $L^2$-spaces. We consider the measurable, the topological and the geometric setting respectively. In the measurable setting, we deal with arbitrary (irreducible) Dirichlet forms and show that any intertwining order isomorphism is necessarily unitary (up to a constant). In the topological setting we deal with quasi-regular forms and show that any intertwining order isomorphism induces a quasi-homeomorphism between the underlying spaces. In the geometric setting we deal with both regular Dirich…
Recently representation theory has been used to provide atomic decompositions for a large collection of classical Banach spaces. In this paper we extend the techniques to also include projective representations. As our main application we obtain atomic decompositions of Bergman spaces on the unit ball through the holomorphic discrete series for the group of isometries of the ball.
Totally null sets and capacity in Dirichlet type spaces
该研究在$\u2102^d$单位球的Dirichlet型空间框架下，证明了单位球面紧子集的完全零概念与零容量概念等价，并结合已有峰值插值结果强化了经典边界插值定理。
We consider the Dirichlet problem for semilinear elliptic equations on a bounded domain which is diffeomorphic to a ball and investigate bifurcation from a given (trivial) branch of solutions, where the radius of the ball serves as bifurcation parameter. Our methods are based on well known results from variational bifurcation theory, which we outline in a separate section for the readers' convenience.
In this paper, we introduce a unitary invariant $Γ$ defined on the unit ball of $B(H)^n$ in terms of the characteristic function, the noncommutative Poisson kernel, and the defect operator associated with a row contraction. We show that $Γ$ detects the pure row isometries and completely classify them up to a unitary equivalence. We also show that $Γ$ detects the pure row contractions with polynomial characteristic functions and completely non-coisometric row contractions. In particular, we show that any completely non-coisometric row contraction with constant characteristic function is homogen…
The aim of the present paper is three folds. For a reproducing kernel Hilbert space $\mathcal{A}$ (R.K.H.S) and a $σ-$finite measure space $(M_{1},dμ_{1})$ for which the corresponding $L^{2}-$space is a separable Hilbert space, we first build an isometry of Bargmann type as an integral transform from $L^{2}(M_{1},dμ_{1})$ into $\mathcal{A}$. Secondly, in the case where there exists a $σ-$finite measure space $(M_{2},dμ_{2})$ such that the Hilbert space $L^{2}(M_{2},dμ_{2})$ is separable and $\mathcal{A}\subset L^{2}(M_{2},dμ_{2})$ the inverse isometry is also given in an explicit form as an in…
Dirichlet--Neumann bracketing for nonlocal operators
本文在有界Lipschitz域上为完全Bernstein函数的非局部算子的Dirichlet特征值建立Dirichlet--Neumann括号估计，证明特征值介于拉普拉斯算子的Neumann与Dirichlet特征值之间，并推广了分数幂情形的已知结果。
We show that the asymptotic behavior of the partial sums of a sequence of positive numbers determine the local behavior of the Hilbert space of Dirichlet series defined using these as weights. This extends results recently obtained describing the local behavior of Dirichlet series with square summable coefficients in terms of local integrability, boundary behavior, Carleson measures and interpolating sequences. As these spaces can be identified with functions spaces on the infinite-dimensional polydisk, this gives new results on the Dirichlet and Bergman spaces on the infinite dimensional poly…
We apply the Davies method to give a quick proof for upper estimate of the heat kernel for the non-local Dirichlet form on the ultra-metric space. The key observation is that the heat kernel of the truncated Dirichlet form vanishes when two spatial points are separated by any ball of radius larger than the truncated range. This new phenomenon arises from the ultra-metric property of the space.
On a class of left ideals of nest algebras
本文研究由全序偏等距族确定的巢代数左理想，刻画了其为子代数的充要条件，并证明其可分解性、有限秩算子强稠密性及方程可解条件。
The paper is concerned with the interconnection of the boundary behaviour of the solutions of the exterior Dirichlet and Neumann problems of harmonic analysis for the three-dimensional unit ball with the corresponding behaviour of the associated ergodic inverse problems for the punched unlimited space. The basis is the theory of semigroups of linear operators mapping a Banach space $X$ into itself. The rates of approximation play a basic role. Another tool is a Drazin-like inverse operator $B$ for the infinitesimal generator $A$ of a semigroup that arises naturally in ergodic theory. This oper…
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