Differential Operator Matrices of Mixed Order with Periodic Coefficients
We study spectral properties of 2 x 2 operator matrices H defined in the Hilbert space ℍ = L 2(R) x L 2(R)by linear differential systems of mixed order with periodic coefficients. We prove that the spectrum σ (H) of H has a band and gap structure and consists of two band sequences one of which, when infinite, has a finite accumulation point, and give sufficient conditions for this accumulation to take place.
AMS Subject Classification47A10 47E05 34B05 34L05
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