In section 7.3 of Ryder's "Quantum Field Theory", the "complete" or "dressed" propagator is defined to be the two-point function to all orders of the perturbation expansion. It is denoted in (7.71) as [tex]G_c^{(2)}(x, y)[/tex]. It changes the bare mass to the physical mass. My question is, why aren't contributions from other n-point functions considered for this definition? For example, the 4-point function contains also disconnected graphs that modify the propagator.(adsbygoogle = window.adsbygoogle || []).push({});

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# Definition of the dressed propagator

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