Spectra of definite type in waveguide models

Lotoreichik, Vladimir; Siegl, Petr (2017). Spectra of definite type in waveguide models. Proceedings of the American Mathematical Society, 145(3), pp. 1231-1246. American Mathematical Society 10.1090/proc/13316

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We develop an abstract method to identify spectral points of definite type in the spectrum of the operator T₁ ⊗ I₂ + I₁ ⊗ T₂. The method is applicable in particular for non-self-adjoint waveguide type operators with symmetries. Using the remarkable properties of the spectral points of definite type, we obtain new results on realness of weakly coupled bound states and of low lying essential spectrum in the PT-symmetric waveguide. Moreover, we show that the pseudospectrum has a normal tame behavior near the low lying essential spectrum and exclude the accumulation of non-real eigenvalues to this part of the essential spectrum. The advantage of our approach is particularly visible when the resolvent of the unperturbed operator cannot be explicitly expressed and most of the mentioned spectral conclusions are extremely hard to prove using direct methods.

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