Rigged Hilbert Space of Free Coherent States and p-Adic Numbers

We investigate the rigged Hilbert space of free coherent states. We prove that this rigged Hilbert space is isomorphic to the space of generalized functions over a p-adic disk. We discuss the relation of the described isomorphism of rigged Hilbert spaces and noncommutative geometry and show that the considered example realizes the isomorphism between the noncommutative line and the p-adic disk.     

Some geometrical questions in rigged Hilbert spaces

In a rigged Hilbert space Galois correspondences between classes of linear manifolds closed in various norms are studied. The class of linear manifolds closed simultaneously in two norms is investigated. Applications to the theory of representations of closed operators with improper scale subspaces are indicated.Translated from Matematicheskie Zametki, Vol. 13, No. 3, pp. 395–402, March, 1973.     

Questions in the theory of the extension of unbounded operators in rigged Hilbert spaces

Questions are considered related to the application of the methods of the theory of rigged Hilbert spaces to the theory of extending Hermitian operators.Translated from Itogi Nauki i Tekhniki, Matematicheskii Analiz, Vol. 14, pp. 59–100, 1977.     

Exact g-frames in Hilbert spaces

G-frames, which were considered recently as generalized frames in Hilbert spaces, have many properties similar to those of frames, but not all the properties are similar. For example, exact frames are equivalent to Riesz bases, but exact g-frames are not equivalent to g-Riesz bases. In this paper, we firstly give a characterization of an exact g-frame in a complex Hilbert space. We also obtain an equivalent relation between an exact g-frame and a g-Riesz basis under some conditions. Lastly we consider the stability of an exact g-frame for a Hilbert space under perturbation. These properties of exact g-frames for Hilbert spaces are not similar to those of exact frames.     

Hilbert空间中的g-Riesz框架

g-框架作为Hilbert空间中的推广框架最近被提出,它们有许多和框架类似的性质,但并不是所有的性质都是相似的.Christensen已指出了每个Riesz框架都包含一个Riesz基.本文指出并不是所有的g-Riesz框架都包含一个g-Riesz基,但我们得到了每个g-Riesz框架都包含一个无冗g-框架,同时给出了H...     

Symmetric Hilbert spaces arising from species of structures

Symmetric Hilbert spaces such as the bosonic and the fermionic Fock spaces over some lsquo;one particle space’ are formed by certain symmetrization procedures performed on the full Fock space. We investigate alternative ways of symmetrization by building on Joyal's notion of a combinatorial species. Any such species F gives rise to an endofunctor of the category of Hilbert spaces with contractions mapping a Hilbert space to a symmetric Hilbert space with the same symmetry as the species F. A general framework for annihilation and creation operators on these spaces is developed, and compared to the generalised Brownian motions of R. Speicher and M. Bożejko. As a corollary we find that the commutation relation with admits a realization on a symmetric Hilbert space whenever f has a power series with infinite radius of convergence and positive coefficients. Received: 7 April 2000; in final form: 28 November 2000 / Published online: 19 October 2001     

Partial Multiplication of Operators in Rigged Hilbert Spaces

The problem of the multiplication of operators acting in rigged Hilbert spaces is considered. This is done, as usual, by constructing certain intermediate spaces through which the product can be factorized. In the special case where the starting space is the set of C-vectors of a self-adjoint operator A, a general procedure for constructing a special family of interspaces is given. Their definition closely reminds that of the Bessel potential spaces, to which they reduce when the starting space is the Schwartz space Some applications are considered.     

The connection between the rigged Hilbert space and the complex scaling approaches for resonances. The Friedrichs model

The rigged Hilbert space approach and the complex scaling method are compared for the Friedrichs model. It is shown that they define the same resonance pole. The choice of the test space for the rigged Hilbert space approach is discussed.     

Closed embeddings of Hilbert spaces

Motivated by questions related to embeddings of homogeneous Sobolev spaces and to comparison of function spaces and operator ranges, we introduce the notion of closely embedded Hilbert spaces as an extension of that of continuous embedding of Hilbert spaces. We show that this notion is a special case of that of Hilbert spaces induced by unbounded positive selfadjoint operators that corresponds to kernel operators in the sense of L. Schwartz. Certain canonical representations and characterizations of uniqueness of closed embeddings are obtained. We exemplify these constructions by closed, but not continuous, embeddings of Hilbert spaces of holomorphic functions. An application to the closed embedding of a homogeneous Sobolev space on Rn in L₂(Rn), based on the singular integral operator associated to the Riesz potential, and a comparison to the case of the singular integral operator associated to the Bessel potential are also presented. As a second application we show that a closed embedding of two operator ranges corresponds to absolute continuity, in the sense of T. Ando, of the corresponding kernel operators.     

Triplet extensions I: Semibounded operators in the scale of Hilbert spaces

The extension theory for semibounded symmetric operators is generalized by including operators acting in a triplet of Hilbert spaces. We concentrate our attention on the case where the minimal operator is essentially self-adjoint in the basic Hilbert space and construct a family of its self-adjoint extensions inside the triplet. All such extensions can be described by certain boundary conditions, and a natural counterpart of Krein’s resolvent formula is obtained.     

Complex structures on twisted Hilbert spaces

We investigate complex structures on twisted Hilbert spaces, with special attention paid to the Kalton–Peck Z₂ space and to the hyperplane problem. For any non-trivial twisted Hilbert space, we show there are always complex structures on the natural copy of the Hilbert space that cannot be extended to the whole space. Regarding the hyperplane problem we show that no complex structure on ?₂ can be extended to a complex structure on a hyperplane of Z₂ containing it.     

Box spaces,group extensions and coarse embeddings into Hilbert space

We investigate how coarse embeddability of box spaces into Hilbert space behaves under group extensions. In particular, we prove a result which implies that a semidirect product of a finitely generated free group by a finitely generated residually finite amenable group has a box space which coarsely embeds into Hilbert space. This provides a new class of examples of metric spaces with bounded geometry which coarsely embed into Hilbert space but do not have property A, generalising the example of Arzhantseva, Guentner and Spakula.     

Reproducing kernel Hilbert spaces associated with kernels on topological spaces

We analyze reproducing kernel Hilbert spaces of positive definite kernels on a topological space X being either first countable or locally compact. The results include versions of Mercer’s theorem and theorems on the embedding of these spaces into spaces of continuous and square integrable functions.     

Non-factorizable extensions of the Liouville operator: the Friedrichs model

We construct for the Friedrichs model extensions of the Liouville operator which do not reduce to any extension of the corresponding Hamilton operator. These extensions originate in the Brussels–Austin approach to irreversibility and acquire meaning in suitable rigged Hilbert spaces (RHS) associated with the Hilbert–Schmidt space, known as rigged Liouville space (RLS).     

Ultrametric spaces and related Hilbert spaces

We present simple proofs of the possibility of embedding ultrametric spaces in Hilbert spaces. The main part of the paper deals with ultrametric spaces that we call totally infinite spaces. Related Hilbert spaces, automorphisms of totally infinite spaces, and the corresponding linear operators are considered. Transplated fromMatematicheskie Zametki, Vol. 62, No. 2, pp. 223–237, August, 1997. Translated by V. E. Nazaikinskii     

Spectrum of a linear operator in a family of banach spaces containing Hilbert space

The mutual relation is established between the spectra of a bounded linear operator acting in a family of Banach spaces. It is assumed in addition that one of the spaces is a Hilbert space and that the operator acting on it is self-adjoint. An example is presented illustrating the properties proved.Translated from Matematicheskie Zametki, Vol. 22, No. 4, pp. 495–498, October, 1977.     

An estimate of the Banach-Mazur distances between Hilbert spaces and Banach spaces

We discuss a geometric property that provides tools for the estimate of the Δ₂ on spaces of Rademacher functions with values on a Banach space for particular sequences of vectors. We obtain in this way a technique to study those Banach spaces that are isomorphic to Hilbert spaces. In particular, an estimate of the Banach-Mazur distance between such these spaces is obtained.     

Compact composition operators on weighted Hilbert spaces of analytic functions

We characterize the compactness of composition operators acting on a large family of Hilbert spaces of analytic functions which lie between Bergman and Dirichlet spaces. Our characterization is given in terms of generalized Nevanlinna counting functions.     

The comparison theorem for Hilbert spaces of entire functions

A generalization of the Sturm comparison theorem is obtained for formally self-adjoint ordinary differential operators of finite order given in canonical form. The result is stated within the vector theory of Hilbert spaces of entire functions when the coefficient space is a finite-dimensional vector space.