- #1

ShayanJ

Gold Member

- 2,791

- 591

## Summary:

- Trying to figure out Feynman rules from expansion of the generating functional.

I'm reading "introduction to many body physics" by Piers Coleman. In section 7.2 he's trying to introduce Feynman diagrams by expanding the generating functional. But first he transforms it into this pictorial form:

Then he calculates the n=1, m=1 term like below:

Which I understand. But I have no idea how he calculates the n=1, m=2 term:

Can anybody help?

Thanks

PS

d1 and 1 mean ##dt_1 dx_1## and ##(t_1,x_1)##

Then he calculates the n=1, m=1 term like below:

Which I understand. But I have no idea how he calculates the n=1, m=2 term:

Can anybody help?

Thanks

PS

d1 and 1 mean ##dt_1 dx_1## and ##(t_1,x_1)##