03-507 Derezi\'{n}ski J., Fr\"uboes R.
Level Shift Operator and 2nd order perturbation theory (50K, LATeX 2e) Nov 21, 03
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Abstract. e study spectral properties of linear operators. The main tool is the so-called {\em Level Shift Operator}, which expresses the effects of 2nd order perturbation theory on the point spectrum. We give estimates for the location of the spectrum in a selected region and approximate formulas for the corresponding spectral projections. Presented results are quite robust---they are applicable even if the spectrum in this region has infinite multiplicity.

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