Identical particles and Feynman diagrams

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Discussion Overview

The discussion centers around the treatment of identical particles in quantum field theory (QFT), specifically regarding the computation of the scattering amplitude (M) and the implications for Feynman diagrams. Participants explore the nuances of how identical particles affect calculations and the associated Feynman rules.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that the computation for M will differ when identical particles are present and seeks clarification on how to compute it.
  • Another participant mentions a combinatorial factor that must be divided when calculating the amplitude for scattering processes involving identical particles, suggesting it is detailed in the Feynman rules.
  • A later reply reiterates the need for a combinatorial factor but questions whether this factor addresses the computation of M directly, implying that there may not be a special treatment for identical particles.
  • One participant points out that different Feynman diagrams contribute when particles are identical, providing examples of how electron-muon and electron-electron scattering differ in their diagrammatic representations.

Areas of Agreement / Disagreement

Participants express differing views on whether there is a special treatment for identical particles in the computation of M. Some agree on the necessity of a combinatorial factor, while others question its relevance to the overall computation.

Contextual Notes

The discussion highlights potential limitations in understanding the specific implications of identical particles on the M matrix and the role of Feynman diagrams, with some assumptions about the applicability of combinatorial factors remaining unresolved.

taishizhiqiu
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In Introduction to QFT (peskin) 4.5, he writes:

The computation for M, of course, will be quite different when identical particles are present.

However, I have finished reading the first part of the book and found no special treatment for identical particles. Can anybody tell me how to compute M if identical particles are present?
 
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There is a combinatorial factor you must divide by when computing the amplitude for a scattering process involving identical particles. It's in the Feynman rules so look in the index for the section on them.
 
WannabeNewton said:
There is a combinatorial factor you must divide by when computing the amplitude for a scattering process involving identical particles. It's in the Feynman rules so look in the index for the section on them.

But that's not about computing M matrix. So basically there's nothing special for identical particles?
 
Different Feynman diagrams contribute if the particles are identical. For example, electron-muon scattering has only one diagram at tree level (t-channel photon exchange), but electron-electron scattering has two (t-channel and u-channel photon exchange).
 

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