- #1
chern
- 10
- 0
I learn quantum field theory using the book of " quantum field theory in a nutshell" by A. Zee. But I am confuse when I read the content about the "baby problem" at the beginning of "1.7 Feynman Diagrams". In that section, author get the term of order λ and [J][/4] by -(λ/4!)[(d/dJ)][/4] [1/4![2[m][/2]][/4]][J][/8]. My question is how to draw the figures in I.7.1 according to the result? why are there three figures? There is only one term, why do we get three figures? Thank you !