M. Gamal’

activity

20242026

collaborators

3 papers

math.FA2026

Non-stable subnormal contractions have nontrivial hyperinvariant subspaces

Maria F. Gamal'

A contraction $T$ on a (complex, separable) Hilbert space is stable, or of class $C_{0 \cdot}$ , if $T^{n} \to 0$ in the strong operator topology. It is proved that for a non-stable pur…

math.FA2025

Some relationships with subnormal operators and existence of hyperinvariant subspaces

Maria F. Gamal'

If $T$ is a polynomially bounded operator, $M$ is an invariant subspace of $T$ , $T ∣_{M}$ is a unilateral shift and $T^{*} ∣_{M^{⊥}}$ is subnormal, then $T…

math.FA2024

Examples of cyclic polynomially bounded operators that are not similar to contractions

Maria F. Gamal'

A question if a polynomially bounded operator is similar to a contraction was posed by Halmos and was answered in the negative by Pisier. His counterexample is an operator of infin…