I'm trying to elucidate certain concepts about time dependence and perturbation theory in quantum mechanics and QFT.(adsbygoogle = window.adsbygoogle || []).push({});

I get the impression that most of the important results that in principle can be considered to have a time dependence can actually be calculated in terms of time-independent perturbation methods. I'm thinking for example about the case of scattering both in QM and QFT particle physics, where most of the important calculations like scattering cross-sections, decay rates, energies of bound states, etc can be made by matching the asymptotic states of the time-independent Hamiltonian in the context of the S-matrix.

Or the use of the Dyson series in the context of the Feynman diagrams in QED perturbative renormalization.

And Fermi's golden rule wich is a time-dependent perturbation derivation that can also be used in the context of time-independent problems.

It seems the strict time-dependent perturbation is only needed to obtain the quantum transition probabilities under a external perturbation.

Is the above impression correct, or is it wrong and if so can someone give examples of applications or physical problems where the time-dependent perturbation is used in the everyday practice either within the formal obtention of transition probabilities or beyond?

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# Time dependence in quantum theory

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