Hyponormal differential operators with discrete spectrum

Almost α-Hyponormal Operators with Weyl Spectrum of Area Zero

Polynomially hyponormal operators

A survey of the theory of k-hyponormal operators starts with the construction of a polynomially hyponormal operator which is not subnormal. This is achieved via a natural dictionary between positive functionals on specific convex cones of polynomials and linear bounded operators acting on a Hilbert space, with a distinguished cyclic vector. The class of unilateral weighted shifts provides an op...

ON p-HYPONORMAL OPERATORS

In this paper we show that p-hyponormal operators with 0 / ∈ σ(|T | 1 2 r ) are subscalar. As a corollary, we get that such operators with rich spectra have non-trivial invariant subspaces.

Hyponormal Composition Operators

In [1] D. Harrington and R. Whitley examined several questions of seminormality for composition operators. In that article they raise the question of finding a measure theoretic characterization of hyponormality for composition operators. In this article we establish criteria for hyponormality for weighted composition operators. By restricting attention to the case of weight function equal to 1...

On the Discrete Spectrum of a Family of Differential Operators

A family Aα of differential operators depending on a real parameter α is considered. The problem can be formulated in the language of perturbation theory of quadratic forms. The perturbation is only relatively bounded but not relatively compact with respect to the unperturbed form. The spectral properties of the operator Aα strongly depend on α. In particular, for α < √ 2 the spectrum of Aα bel...