How Does the n Factor Arise in the QFT Generating Functional Equation?

  • Thread starter Thread starter binbagsss
  • Start date Start date
  • Tags Tags
    Functional Qft
Click For Summary
The discussion focuses on understanding the emergence of the n factor in the QFT generating functional equation. The user is attempting to differentiate the generating functional and is confused about how the n factor arises from the terms involved. They note that while differentiating yields a G_{n-1} term, the additional term S'[\Phi] + J may contribute to the n factor. The user is also considering the placement of J in the integral and how it affects the differentiation process. Overall, they are seeking clarification on the relationship between these elements to better understand the equation.
binbagsss
Messages
1,291
Reaction score
12

Homework Statement



Hi

I am looking at the attached question part c)

generatingfunctional2.jpg


Homework Equations



below

The Attempt at a Solution



so if i take ##\frac{\partial^{(n-1)}}{\partial_{(n-1)}} ## of (2) it is clear I can get the ##\frac{i}{h} (\lambda_2 +\lambda_4 )## like-term, but I am unsure about the ##nG_{n-1}## .

There's obviously no other derivatives on the RHS so I will only yield a ##G_{n-1}## and that looks fine, I am a bit confused though, I can yield this from the ## Z[J] ## alone on the RHS, whereas the RHS is ##Z[J]## 'multiplied by' (it is already inside the integral) the extra term of ##S'[\Phi] + J## . So I suspect this extra term is the reason we get the ##n## factor but I am unsure how.

Looking at the LHS there is a single ##J## so it looks like this gives a factor of ##1## and then we take across ##(n-1)## from the RHS.

If I take a derivative wrt ##J##, on the LHS I can either act on the exponential or the single ##J## (but can only act on this ##J## once,) on the RHS it's the same story, with the difference that on the LHS the ##J## is outside the integral but on the RHS it is inside the integral, I'm trying to use this to deduce where the factor of ##n## comes from but I am struggling..
 

Attachments

  • generatingfunctional2.jpg
    generatingfunctional2.jpg
    38 KB · Views: 900
Physics news on Phys.org
bump
many thanks
 

Similar threads

Replies
1
Views
2K
Replies
2
Views
2K
Replies
1
Views
2K
  • · Replies 1 ·
Replies
1
Views
429
Replies
10
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 2 ·
Replies
2
Views
3K
Replies
4
Views
5K
  • · Replies 1 ·
Replies
1
Views
2K