Chafiq Benhida

Finite rank perturbations of contractions

We study finite rank perturbations of contractions of classC.0 with finite defect indices. The completely nonunitary part of such a perturbation is also of classC.0, while the unitary part is singular. When the defect indices of the original contraction are not equal, it can be shown that almost always (with respect to a suitable measure) the perturbation has no unitary part.

Functional models and finite dimensional perturbations of the shift

We study finite dimensional perturbations of shift operators and their membership to the classes Am, n appearing in the theory of dual algebras. The results obtained yield informations about the lattice of invariant subspaces via the techniques of Scott Brown.

Propriétés spectrales des restrictions d'opérateurs de la classe \(\mathbb{A}\)

AbstractWe discuss here the question whether there exists an invariant subspace

Numerical Ranges of C 0 ( N ) Contractions

M

Unitary equivalence of operators and dilations

for a contraction T in the class

L^2

\mathbb{A}