Feynman Diagrams, are these allowed?

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Homework Help Overview

The discussion revolves around the validity of Feynman diagrams in particle physics, specifically regarding their legality and appropriateness in certain interactions. Participants are exploring the nuances of diagram construction and the implications of different particle interactions.

Discussion Character

  • Conceptual clarification, Assumption checking, Mixed

Approaches and Questions Raised

  • Participants discuss the legality of various Feynman diagrams, questioning the presence of certain particles and the implications of energy levels on diagram relevance. There are inquiries about modifications to improve the diagrams, such as replacing particles and adjusting orientations to resolve charge issues.

Discussion Status

The discussion is active, with participants providing insights on the rules of thumb for diagram construction and addressing specific concerns raised by the original poster. Some guidance has been offered regarding potential fixes for identified issues, but there is no explicit consensus on the overall legality of the diagrams.

Contextual Notes

Participants are operating under the constraints of typical rules in particle physics regarding interaction strengths and energy considerations, which are being questioned and examined throughout the discussion.

NumberBucket
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Homework Statement
I have drawn a couple of diagrams for each of the two following equations. Are any of them wrong? Are either preferred? I don't have much practice with drawing these...
Relevant Equations
electron + positron -> tau+ anti-tau
electron + positron -> tau-neutrino + anti-tau-neutrino
Capture1.PNG


Capture2.PNG

These are my attempts, I have found two possibilities for each, but have no idea if they're 'legal'...

Thanks in advance!
 
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As a rule of thumb: strong > electromagnetic > weak, and tree-level > loops
While the diagrams are possible (except for the signs in the second one, check these) there is a much more important diagram for tau+antitau unless you are close to the Z energy in the collision.
The fourth diagram has additional particles that shouldn't be there.
 
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mfb said:
As a rule of thumb: strong > electromagnetic > weak, and tree-level > loops
While the diagrams are possible (except for the signs in the second one, check these) there is a much more important diagram for tau+antitau unless you are close to the Z energy in the collision.
The fourth diagram has additional particles that shouldn't be there.
Ah ok, thanks! So would the first one be better with a photon then? And would flipping the RHS of the second one fix the charge issues?
 
"Better" is subjective. "Stronger" at low energies: Certainly.

Yes, flipping the RHS will fix it.
 
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