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Correlation Function and Generating Functional in QED
Peskin and Schroeder (1995, p.82 and p.292) define the two-point correlation function of a $\phi^4$ theory as
$$\langle \Omega|T\{\phi(x)\phi(y)\}|\Omega\rangle\tag{4.10}$$
and the generating ...
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How to write the spatial photon propagator of the generating function $Z[J]$ in QED?
There was a part in the lecture one didn't quite understand. (The charge $e=0$ in this post.) The partition function for massive fields such as scalar fields or the spin-1/2 fields were quite standard....
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One-loop effective action of QED and the partition function
Given the partition function for QED
$$ Z= \int \mathcal{D}A_{\mu}\mathcal{D}\Psi \mathcal{D}\bar{\Psi}\, \text{exp}\left(- \frac{i}{4}\int F_{\mu\nu} F^{\mu\nu} + i \int \bar{\Psi} (i {\not} D-m) \...
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