On the representation of effective quantum field theories

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We discuss a general model for effective quantum field theories (QFTs), which for example comprises quantum chromodynamics and quantum electrodynamics. We assume in the model a perturbative expansion of the Lagrangian with respect to a cut-off-energy parameter. For each order in the expansion we rigorously derive a representation, which is unitarily equivalent to the representation of the effective QFT in the non-interaction approximation. We interpret the various representations as different particle pictures with respect to which the effective QFT can be described. We further derive a rigorous scattering theory, which exactly reproduces results of formal scattering theory in quantum field theory.