Self Energy for N flavor phi^4 theory

  • Thread starter psi*psi
  • Start date
  • #1
6
0
I am reading the fifth chapter on perturbation theory of Condensed Matter Field Theory by Altland and Simons. This question is about the section starting on page 223.

To discuss self energy, they introduced a vector field ##\phi = \{ \phi^a \}, a = 1, \cdots , N##. The action of the field is given by
[tex]
S[\phi] = \int d^dx (\frac{1}{2} \partial \phi \cdot \partial \phi + \frac{r}{2} \phi \cdot \phi + \frac{g}{4 N} (\phi \cdot \phi)^2)
[/tex]
The goal is to compute the perturbation expansion of the Green function
[tex]
G^{ab}(x-y)=\langle \phi^a (x) \phi^b (y)\rangle
[/tex]
using the self energy operator ##\Sigma_p##.

In momentum space, the Green function is given by
[tex]
G^{ab}_{p} = [(p^2+r- \hat \Sigma_p)^{-1}]^{ab},
[/tex]
where the diagrams for ## \Sigma_p ## is shown in the figure
upload_2014-12-23_12-34-51.png

The text claims that represented in terms of the Green functions, the first order contribution to the self-energy operator is given by
[tex]
[\Sigma^{(1)}_{\mathbf{p}}]^{ab} = - \delta^{ab} \frac{g}{L^d} (\frac{1}{N} \sum_{\mathbf{p'}} G_{0,\mathbf{p'}} + \sum_{\mathbf{p'}} G_{0,\mathbf{p-p'}}),
[/tex]
where the first (second) term in the parenthesis corresponds to the first (second) diagram in the figure. I am having trouble reproducing this result. Specifically,
(1) Where does the overall minus sign come from?
(2) Since the interaction strength is given by ##g/4N##, from the result, the first diagram has a contribution of ##4## and the second diagram has a contribution of ##4N##. How do I get these factors?
(3) How do I derive the Feynman rules for these diagrams?

Thanks.
 

Answers and Replies

  • #2
18,363
8,213
Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
 

Related Threads on Self Energy for N flavor phi^4 theory

Replies
2
Views
2K
  • Last Post
Replies
4
Views
286
  • Last Post
Replies
3
Views
5K
Replies
1
Views
252
  • Last Post
2
Replies
29
Views
8K
  • Last Post
Replies
2
Views
238
  • Last Post
Replies
0
Views
274
Replies
0
Views
201
Replies
5
Views
3K
Replies
6
Views
267
Top