Definition of the dressed propagator

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SUMMARY

The "dressed" propagator, as defined in section 7.3 of Ryder's "Quantum Field Theory," is the two-point function encompassing all orders of the perturbation expansion, represented as G_c^{(2)}(x, y). This propagator effectively transitions the bare mass to the physical mass. The discussion clarifies that contributions from n-point functions, such as the 4-point function, are not included in this definition because the propagator is fundamentally a two-point function, regardless of whether the graphs are connected or disconnected.

PREREQUISITES
  • Understanding of quantum field theory concepts
  • Familiarity with perturbation theory
  • Knowledge of two-point and n-point functions
  • Acquaintance with Ryder's "Quantum Field Theory" (specific section 7.3)
NEXT STEPS
  • Study the implications of the dressed propagator in quantum field theory
  • Explore the role of n-point functions in perturbation theory
  • Investigate the relationship between bare mass and physical mass
  • Review connected vs. disconnected graphs in quantum field theory
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Students and researchers in theoretical physics, particularly those focusing on quantum field theory and perturbation methods, will benefit from this discussion.

hellfire
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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 G_c^{(2)}(x, y). 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.
 
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Why should they be? Both for a free and an interacting theory the propagator is the 2 point function by definition (connected or disconnected it doesn't matter, since there are only 2 spacetime points).

Daniel.
 
dextercioby said:
connected or disconnected it doesn't matter, since there are only 2 spacetime points.
Thanks, this makes sense. I was somehow confused, but your comment answers exactly my question.
 

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