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## Main Question or Discussion Point

In peskin chap 4 on interaction field theory, he first introduced some basics about interaction picture(mostly in pg. 83~87) , it seems he assumed the Hamiltonians H=H_0+H_int in Schrodinger picture are all time-independent, because he used quite a lot of notations like exp(iHt), exp(iH_0t) and exp(iH_int t). So does it mean all the perturbation techniques developed later in the book only apply to time-independent interaction?

The specific example he talked about is K-G field with phi^4 interaction, which is indeed time-independent in schrodinger's picture(or not?). However, what happens if we want to calculate a time-dependent interaction? Maybe in practice all scattering processes can be described by time-independent H? If so, how to justify this?

The specific example he talked about is K-G field with phi^4 interaction, which is indeed time-independent in schrodinger's picture(or not?). However, what happens if we want to calculate a time-dependent interaction? Maybe in practice all scattering processes can be described by time-independent H? If so, how to justify this?