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We study second order perturbation theory for embedded eigenvalues of anabstract class of self-adjoint operators. Using an extension of the Mourretheory, under assumptions on the regularity of bound states with respect to aconjugate operator, we prove upper semicontinuity of the point spectrum andestablish the Fermi Golden Rule criterion. Our results apply to masslessPauli-Fierz Hamiltonians for arbitrary coupling.

Second order perturbation theory for embedded eigenvalues