Dirac Operators on a Compact Lie Group

Let K be a compact connected Lie group with a bi-invariant metric( , ) which is k-spin. A Dirac operator D on ‘pure’definite spinors is associated to a left k-invariant, metricconnection on the tangent bundle; D is left k-invariant andelliptic. It is shown that the dimension of the kernel of D (the spaceof harmonic spinors) depends on the choice of connection. Infact for a real family of connections _a(obtained via the adjointrepresentation of K) the subrepresentation of the left regularrepresentation of K on the space of harmonic spinors is determined,and a dimension formula is given.     

Compact and Weakly Compact Composition Operators on BMOA

Any analytic map φ of the unit disc ${\mathbb{D}}$ into itself induces a composition operator C _φ on BMOA, mapping ${f \mapsto f \circ \varphi}$ , where BMOA is the Banach space of analytic functions ${f\colon \mathbb{D} \to \mathbb{C}}$ whose boundary values have bounded mean oscillation on the unit circle. We show that C _φ is weakly compact on BMOA precisely when it is compact on BMOA, thus solving a question initially posed by Tjani and by Bourdon, Cima and Matheson in the special case of VMOA. As a crucial step of our argument we simplify the compactness criterion due to Smith for C _φ on BMOA and show that his condition on the Nevanlinna counting function alone characterizes compactness. Additional equivalent compactness criteria are established. Furthermore, we prove the unexpected result that compactness of C _φ on VMOA implies compactness even from the Bloch space into VMOA.     

关于压缩算子的不变子空间

证明关于压缩算子的如下不变子空间定理：如果T是Hilbert空间H上的压缩算子,且集合Z’={λ∈D;存在z∈H,使得‖z‖=1,且‖（λ-T）z‖＜1/3(1-‖λ‖}是开单位圆D的控制集,那么T有非平凡的不变子空间,这个定理包含了S.Brown,B.Chevreau,C.fPearcy和B.Beauzamy的两个重要结果作为特殊情况,特别是,为个定理包含了S.Brown等人的Hilbert空间上的每个具有厚谱的压缩算子都有平凡的不变子空间这个重要结果作为特殊情况。     

Compact Composition Operators on BMOA

We characterize the compact composition operators on BMOA, the space consisting of those holomorphic functions on the open unit disk that are Poisson integrals of functions on , that have bounded mean oscillation. We then use our characterization to show that compactness of a composition operator on BMOA implies its compactness on the Hardy spaces (a simple example shows the converse does not hold). We also explore how compactness of the composition operator relates to the shape of near , introducing the notion of mean order of contact. Finally, we discuss the relationships among compactness conditions for composition operators on BMOA, VMOA, and the big and little Bloch spaces.

     

Compact Operators on Bergman Spaces

We prove that a bounded operator S on L _a ^p for p > 1 is compact if and only if the Berezin transform of S vanishes on the boundary of the unit disk if S satisfies some integrable conditions. Some estimates about the norm and essential norm of Toeplitz operators with symbols in BT are obtained.     

Grothendieck Spaces of Compact Operators

In this paper we study the Grothendieck spaces among the operator spaces L_e(E'_c, F). Conditions under which L_e(E'_c, F) contains complemented copy of c₀ are given. We apply these results to spaces of the type C_b(X; F) endowed with strict topologies.     

Dirichlet空间上的紧算子

若S是Dirichlet空间上有限个Toeplitz算子乘积的有限和, S为紧算子的充要条件是: 当z→∂D时, S的Berezin型变换收敛到0; 若S是Dirichlet空间上Hankel算子, S为紧算子的充要条件是: 当z→ D时, S作用在类再生核上按范数收敛到0.     

Triangularizability of Polynomially Compact Operators

An operator on a complex Banach space is polynomially compact if a non-zero polynomial of the operator is compact, and power compact if a power of the operator is compact. Theorems on triangularizability of algebras (resp. semigroups) of compact operators are shown to be valid also for algebras (resp. semigroups) of polynomially (resp. power) compact operators, provided that pairs of operators have compact commutators.     

Characterization of Operators on the Dual of Hypergroups which Commute with Translations and Convolutions

For a locally compact group G, L^1 (G) is its group algebra and L^∞(G) is the dual of L^1 (G).Lau has studied the bounded linear operators T:L^∞(G)→L^∞(G) which commute with convolutions and translations. For a subspace H of L^∞(G), we know that M(L^∞(G),H), the Banach algebra of all bounded linear operators on L^∞(G) into H which commute with convolutions, has been studied by Pyre and Lau. In this paper, we generalize these problems to L(K)^*, the dual of a hypergroup algebra L(K) in a very general setting, i.e. we do not assume that K admits a Haar measure. It should be noted that these algebras include not only the group algebra L^1(G) but also most of the semigroup algebras.Compact hypergroups have a Haar measure, however, in general it is not known that every hypergroup has a Haar measure. The lack of the Haar measure and involution presents many difficulties; however,we succeed in getting some interesting results.     

列压缩算子的不动点定理及其应用

本文在无连续性及紧性的假设情况下,讨论了u0-凹的列压缩算子及一类混合单调算子的不动点定理,并给出了在积分方程中的应用.     

Fredholm Operators and Riesz Theory for Polynomially Compact Operators

In this article, we give a characterization of a class of bounded Fredholm operators on a Banach space which is developed to present some general existence results of the operators equation of the second kind. The obtained results are used to describe the Riesz–Schauder theory of compact operators in the more general setting of polynomially compact operators.     

带紧扰动的极大单调算子的满射定理

本文利用逼近方法和Ａｌｔｍａｎ不动点定理获得了带扰动的极大单调算子几个满射定理。     

带紧扰动的极大单调算子的零点定理

使用Leray-Schauder度理论研究了带紧扰动的极大单调算子的零点问题,获得了一些新的零点定理。     

Singular Values of Compact Pseudodifferential Operators

This paper investigates the asymptotic decay of the singular values of compact operators arising from the Weyl correspondence. The motivating problem is to find sufficient conditions on a symbol which ensure that the corresponding operator has singular values with a prescribed rate of decay. The problem is approached by using a Gabor frame expansion of the symbol to construct an approximating finite rank operator. This establishes a variety of sufficient conditions for the associated operator to be in a particular Schatten class. In particular, an improvement of a sufficient condition of Daubechies for an operator to be trace-class is obtained. In addition, a new development and improvement of the Calderón–Vaillancourt theorem in the context of the Weyl correspondence is given. Additional results of this type are then obtained by interpolation.     

真压缩算子解析函数的优势原理

该文发展ＫｙＦａｎ［１］中定理４的结果,对复的Ｈｉｌｂｅｒｔ空间犎上的真压缩算子犃和单位园盘Δ 内的解析函数犳给出了优势原理．与文［５］比较,该文去掉犃为正规算子的限制,并改进了相应的结果．还对犎（Δ）的某个子类中的犳,给出‖犳′（犃）‖ 的估值．并讨论了从属关系的优势原理,特别是把Ｓｈａｈ Ｇｏｌｕｚｉｎ关于从属于单叶函数的优势半径［７,定理６．７和６．８］拓广到算子函数．     

Coburn Type Operators and Compact Perturbations

A bounded linear operator T acting on a Hilbert space is called Coburn operator if ker(T ? λ) = {0} or ker(T ? λ)^*= {0} for each λ ∈ C. In this paper, the authors define other Coburn type properties for Hilbert space operators and investigate the compact perturbations of operators with Coburn type properties. They characterize those operators for which has arbitrarily small compact perturbation to have some fixed Coburn property.Moreover, they study the stability of these properties under small compact perturbations.