A Note on Spectral Convergence in Varying Hilbert Spaces

We prove sufficient conditions for Hausdorff convergence of the spectra of sequences of closed operators defined on varying Hilbert spaces and converging in norm-resolvent sense, i.e. $\|J_\varepsilon(1+A_\varepsilon)^{-1} - (1+A)^{-1}J_\varepsilon\|\to 0$ as $\varepsilon\to 0$, where $J_\varepsilon$ is a suitable identification operator between the domains of the operators. This is an extension of results of [Mugnolo-Nittka-Post(2013)], who proved absence of spectral pollution for sectorial operators.