Subspace perturbation problems for linear operators

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The project is aimed at studying the perturbation problem for invariant subspaces of linear operators, with emphasis on the case of off-diagonal perturbations. Main goal of the project is to obtain (sharp) norm estimates on the operator angles between the spectral subspaces associated with isolated parts of the spectrum of the perturbed and unperturbed operators. Another goal is to establish new and more precise sufficient conditions for the existence of solutions to the related operator Riccati equations.