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3
votes
1answer
177 views

Feynman Diagram for Bragg Equation

Did Feynman ever derive the Bragg equation as a particle representation using Feynman diagrams? And where is it available? I spoke to Freeman Dyson and he couldn't recall.
3
votes
1answer
389 views

Feynman rule 4-point vertex WW -> ZZ

I am looking for the Feynman rule of the 4-point gauge boson interaction of W+ W- -> Z Z. I am guessing it looks like the Yang Mills 4-point vertex for gluons, but with helicity included. Equation ...
9
votes
2answers
258 views

How to prove equivalence of RG flow of QFT coupling constant and diagrammatic resummation at fixed renormalization scale?

QFT books say that solving the RG equation $\frac {dg} {d\textbf{ln} \mu}=\beta(g)$, using the one-loop beta function, is to the "leading log" approximation equivalent to resumming infinitely many ...
0
votes
3answers
977 views

Conservation of electric charge in Feynman diagram

Here is a Feynman diagram showing the mutual annihilation of a bound state electron positron pair into two photons: Is the electric charge conserved at the point A (or B)? What is the "charge" of ...
2
votes
1answer
204 views

How do you properly define a line in a Feynman diagram?

I've been reading Tony Zee's "Quantum Field Theory" and I'm really enjoying it. However, on p. 45 I came across what I think is an inconsistency. The sentences in question are: The rules go ...
8
votes
2answers
217 views

In what sense are loop diagrams quantum corrections?

What's so not-quantum about tree-level diagrams?
4
votes
1answer
155 views

Convergence of quantum effective action to finite loop order

Consider the quantum effective action of a fixed QFT. If we compute it perturbatively to finite loop order $\ell$, we get a sum over an infinite number of Feynman diagrams. For example, the 1-loop ...
4
votes
3answers
2k views

Electron Positron annihilation Feynman Diagram

I am having some trouble understanding this fenyman diagram, it seems to indicate that the electron produces the positron, as the arrow of the positron is pointing from the electron. Additionally ...
4
votes
1answer
423 views

Help with Cutkosky cutting rules for fermions

I know that a cut boson propagator is replaced with the mass shell delta function. But what happens when you cut a fermion propagator? Do you just replace the denominator with a mass shell delta ...
6
votes
1answer
93 views

Why is there no double counting of $s$- and $t$-channels in string theory?

In string theory for the four particle tree diagram exchange, why is there some mysterious crossing duality between the $s$- and $t$- and $u$-channels? Why isn't there a double counting in the Feynman ...
13
votes
2answers
279 views

Applications of the Feynman-Vernon Influence Functional

I am looking for a reference where the Feynman-Vernon influence functional was defined and used in the context of relativistic quantum field theory. This functional is one method to describe ...