I've been reading these notes and I can't figure out the why on P.120, it is said that
The fermionic statistics mean that the first diagram has an extra minus sign relative to the ψψ scattering of Figure 25.
Would someone mind explaining it to me? I see that the calculations below, illustrating this, but is there an intuitive way of seeing that the signs of the respective first diagrams in Figures 25, 27 should be opposite?
Thank you.
Answer
every time you change two fermions you have to add a minus sign because of spin statistics. lets say for example you have fermion a and fermion b. lets say you have a diagram with two contributions one where fermions a and b interact in some manner, but for the other contribution you have to change the role of fermion a for that of fermion b then you have to add a minus sign.
No comments:
Post a Comment