On Dominating Sequences in the Unit Disc.
On Intertwining Operators.
On Polynomials in Several Hilbert Space Operators.
On the Davis-Kahan-Weinberger Solution of the Norm-Preserving Dilation Problem.
On the Jordan model operators
Operator models and Arveson's curvature invariant
Operator positivity and analytic models of commuting tuples of operators
We study analytic models of operators of class with natural positivity assumptions. In particular, we prove that for an m-hypercontraction on a Hilbert space , there exist Hilbert spaces and ⁎ and a partially isometric multiplier θ ∈ ℳ (H²(),A²ₘ(⁎)) such that and , where A²ₘ(⁎) is the ⁎-valued weighted Bergman space and H²() is the -valued Hardy space over the unit disc . We then proceed to study analytic models for doubly commuting n-tuples of operators and investigate their applications...
Potapov-Ginsburg Transformation and Functional Models of Non-Dissipative Operators
2000 Mathematics Subject Classification: Primary 47A20, 47A45; Secondary 47A48.A relation between an arbitrary bounded operator A and dissipative operator A+, built by A in the following way A+ = A+ij*Q-j, where A-A* = ij*Jj, (J = Q+-Q- is involution), is studied. The characteristic functions of the operators A and A+ are expressed by each other using the known Potapov-Ginsburg linear-fractional transformations. The explicit form of the resolvent (A-lI)-1 is expressed by (A+-lI)-1 and (A+*-lI)-1...
Propriétés analytiques des valeurs et vecteurs propres des opérateurs de l'espace de Hilbert
Propriétés spectrales des restrictions d’opérateurs de la classe
Pseudo almost periodic and automorphic mild solutions to nonautonomous neutral partial evolution equations
In this work, we present a new concept of Stepanov weighted pseudo almost periodic and automorphic functions which is more generale than the classical one, and we obtain a new existence result of μ-pseudo almost periodic and μ-pseudo almost automorphic mild solutions for some nonautonomous evolution equations with Stepanov μ-pseudo almost periodic terms. An example is shown to illustrate our results.
Quasi-similarity of contractions having a 2×1 characteristic function.
Semi-groupes de contractions de classe de l’espace de Hilbert
Smooth operators in the commutant of a contraction
For a completely non-unitary contraction T, some necessary (and, in certain cases, sufficient) conditions are found for the range of the calculus, , and the commutant, T’, to contain non-zero compact operators, and for the finite rank operators of T’ to be dense in the set of compact operators of T’. A sufficient condition is given for T’ to contain non-zero operators from the Schatten-von Neumann classes .
Sobolev- und Sobolev-Hardy-Räume auf S1: Dualitätstheorie und Funktionalkalküle.
Spectral Theory and Sheaf Theory. II.
Spectral theory and sheaf theory. III.
Stability of the bases and frames reproducing kernels in model spaces
We study the bases and frames of reproducing kernels in the model subspaces of the Hardy class in the upper half-plane. The main problem under consideration is the stability of a basis of reproducing kernels under “small” perturbations of the points . We propose an approach to this problem based on the recently obtained estimates of derivatives in the spaces and produce estimates of admissible perturbations generalizing certain results of W.S. Cohn and E. Fricain.
Standard dilations of q-commuting tuples
We study dilations of q-commuting tuples. Bhat, Bhattacharyya and Dey gave the correspondence between the two standard dilations of commuting tuples and here these results are extended to q-commuting tuples. We are able to do this when the q-coefficients are of modulus one. We introduce a “maximal q-commuting subspace” of an n-tuple of operators and a “standard q-commuting dilation”. Our main result is that the maximal q-commuting subspace of the standard noncommuting dilation of a q-commuting...
Sz. Nagy-Foias theory and similarity for a class of Toeplitz operators