Tagged Questions
3
votes
0answers
46 views
A particlar normal ordering problem
Say we have an expression of the form:
$$
\left<0\right|:\phi(x)^2: : \phi(y)^2:\left|0\right>,
$$
where $\phi$ is some scalar field. I have heard the claim several times, that in evaluating ...
0
votes
0answers
65 views
How would I apply Wick's theorem to expand the time-ordered product of three quantum fields? [closed]
I think I understand how to use Wick's theorem to expand the time-ordered product of quantum fields, but I'd like to confirm that. Could you apply Wick's theorem to:
...
8
votes
1answer
145 views
Correlated three-particle Green Function
I know the relationship between normal and correlated two-particle Green Functions for fermions:
$$G_c(1,2,3,4)=\Gamma(1,2,3,4)=G(1,2,3,4)+G(1,3)G(2,4)-G(1,4)G(2,3)$$
Also known as irreducible ...
2
votes
0answers
360 views
How to prove Wick's Theorem (Zee's eq. I.2 (16)) via Gaussian integration?
I'm working through Zee's QFT in a Nutshell but there's an integral [I.2 (16)] I couldn't quite derive.
The problem is to find
$$\langle x_i x_j ... x_k x_l\rangle=\frac{\int ... \int dx_1 ... dx_n ...
3
votes
1answer
706 views
Why/How is this Wick's theorem?
Let $\phi$ be a scalar field and then I see the following expression for the square of the normal ordered version of $\phi^2(x)$.
$$T(:\phi^2(x)::\phi^2(0):) ~=~ 2<0|T(\phi(x)\phi(0))|0>^2 $$
...
2
votes
2answers
948 views
When can I use Wick's theorem?
Wick's theorem means that for fermions, a four point correlation function (for example) can be written in terms of two point correlation functions:
\begin{equation}
\langle b_l^\dagger b_l ...
