orthogonal eigenvectors and Green functions

dimanche 1 septembre 2013

Hi you all. I have to diagonalize a hermitian operator (hamiltonian), that has both discrete and continuous spectrum. If ψ is an eigenvector with eigenvalue in the continuous spectrum, and χ is an eigenvector with eigenvalue in the discrete spectrum, is correct to say that ψ and χ are always mutually orthogonal? I think the answer is yes. But if I numerically calculate the inner product between ψ and χ, then I find that this is far from zero.



PS

I work in this way.

I calculate the eigenvalues and eigenvectors from the Green operator.

Specifically, I have the hamiltonian operator



H = H0 + V



H0 has only continuous spectrum. Using a perturbative expansion, I find the Green operator



G(z) = 1/(z-H)



in terms of V and of the Green operator of H0



G0(z) = 1/(z-H0)



So I find that G(z) has a branch cut and one simple pole. This is consistent with various works and books. Then I calculate the eigenvalues and the corrispondent eigenvectors. So I express ψ and χ in terms of a common basis, and using the Fourier coefficients I can calculate the inner product.






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