Constructing Feynman diagrams and understanding conservation rules.

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In summary, the conversation discusses the rules for constructing Feynman diagrams and the conservation rules related to them. It is mentioned that reactions involving an electron and a photon, or a muon neutrino and an electron antineutrino, are not allowed. This is due to conservation rules such as lepton family number conservation and the fact that weak neutral current only couples to same lepton-antilepton pairs. Finally, it is suggested that using Feynman diagrams may help in understanding these concepts.
  • #1
wam_mi
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Hi guys,

Standard Model


Is this reaction allowed or not? If yes, how do we represent this on Feynman diagram?

(electron) + (photon) ------> (muon negative) + (electron) + positron


What about this reaction?

(muon neutrino) + (electron antinetrino) -----> (muon negative) + (positron)


What are the rules for the construction of Feynman diagrams?
What conservation rules do I need to know?
It would be good if anyone can explain this through Feynman diagrams with a few words. Thanks a lot!
 
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  • #2
is this homework / course work?

Both are not allowed. You need to know about lepton familily number conservation and that weak neutral current (Z boson) couple to same lepton-antilepton pairs (for instance eletron + positron, electron neutrino + anti electron neutrino)
 
  • #3
Within the standard model, the lepton number of each family (electron-like + neutrino-like) is conserved.
 
  • #4
#1 is not allowed to the first order because muon lepton number is not conserved.

#2 is allowed, muon neutrino emits virtual W+ and turns into muon, electron antineutrino eats virtual W+ and becomes a positron. Cross-section is very low.
 

Related to Constructing Feynman diagrams and understanding conservation rules.

What are reactions?

Reactions are processes in which one or more substances are converted into different substances. These conversions often involve the breaking and forming of chemical bonds.

What determines if a reaction is allowed?

The legality of a reaction is determined by the laws of thermodynamics and kinetics. These laws govern the energy changes and rates of reactions, respectively.

What are the factors that affect reaction legality?

The factors that affect reaction legality include the energy of the reactants and products, the presence of a catalyst, the temperature and pressure of the reaction, and the concentration of reactants.

Can reactions be predicted to be allowed or not?

Yes, based on the laws of thermodynamics and kinetics, reactions can be predicted to be allowed or not. However, experimental data may be needed to confirm these predictions.

What happens if a reaction is not allowed?

If a reaction is not allowed, it will not occur or will occur at a very slow rate. In some cases, a different reaction pathway may be needed to make the desired products.

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