Consider that $|\Psi \rangle$ is a scattering state and we have the matrix element $\langle \Psi | \hat{V} | \Psi \rangle$, where $\hat{V}$ is a perturbation. Is t possible expand it using the $S$-matrix? I read in an article that it's possible, but I can't understand how it's done. I suspect that it's related to the Dyson series.


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