Protecting points from operator pencils

Albrecht Seelmann, Matthias Täufer, Krešimir Veselić

We classify all sets of the form ${\bigcup }_{t\in \mathbb{R}}\mathrm{spec}(A+tB)$ where $A$ and $B$ are self-adjoint operators and $B$ is bounded, non-negative, and non-zero. We show…