Feynman Diagrams, are these allowed?

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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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