# Questions tagged [feynman-diagrams]

A diagrammatic technique introduced by Richard Feynman to describe the quantum behaviour of subatomic particles and their interactions. Do not use for general questions on diagrams that are not of the Feynman kind.

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### Does this is an onshell propagator?

This image is from here (page 6-7). My question refers to Eq. 26 and 27 The denominator changed from $(p_1 -p_3)^2 - m^2$ to $p_3^2 - 2p_3p_1$. So they used $p_1^2 = m^2$. But I thought, this relation ...
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### Tadpole diagrams in $\phi^3$ theory

In "Quantum Field Theory" by Mark Srednicki, Chapter 9 page 67, after he proves that $\langle 0|\phi(x)|0 \rangle$ vanishes (meaning sum of all connected diagrams with a single source is zero), he ...
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### Detailed calculation of the scattering amplitude between two particles in $\phi^4$-perturbation theory using the path integral formalism

I'm looking for detailed example/calculation of the scattering amplitude between two particles (mesons) in $\phi^4$-perturbation theory using the path integral formalism. Do anyone of you guys have a ...
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### Problem with the conservation law in Feynman diagram

I have some problem with the virtual particle process as discussed below. We have some interactions that have real photon as produced particle. We consider a tree level Feynman diagram for it and the ...
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Consider a derivative coupling with $$\mathcal{L}_{int} = \lambda \phi_1 (\partial_\mu \phi_2) (\partial_\mu \phi_3),\tag{7.101}$$ and a scalar field $$\phi(x) = \int \frac{d^4p}{(2\pi)^3} \frac{1}{\... 1answer 53 views ### How to calculate the Feynman diagram under SU(N_c) group? I give my own answer below. I use the feynman rules for QCD directly to calculate the process: qq'\rightarrow qq', where q and q' have different flavor. But I don't how to give my answer ... 2answers 70 views ### Physical interpretation of propagator pole In QFT the propagator is divergent for the on-shell momentum of the particles. When e.g. calculating the amplitude for a box loop, the propagator diverges for on-shell particles running in the box-... 0answers 27 views ### Question about gluons and the W-boson regarding Feynman diagrams My questions are: 1) Does a gluon always have no charge? 2) Is the W-boson always positive or negatively charged? I thought these two statements were correct, but I came across an exercise that ... 1answer 37 views ### Question about Feynman diagrams In the picture there are feynman diagrams for two reactions. My question is: Why aren't 6.3 and 6.4 possible for the first reaction? And as a sidenote, I don't really have a good source for the rules, ... 1answer 57 views ### Decay of particle question How would you draw the diagram for the D meson decay mode:$$ D^- \rightarrow K^+ + \pi^- + \pi^- $$1answer 97 views ### Making feynman diagram [closed] I have interaction hamiltonian as$${\cal H}_I = -\frac{1}{2}\sum\limits_{k\neq k',q}\sum\limits_{\sigma,\sigma'}\frac{\omega_{k-k'}M_{k-k'}^2}{\omega_{k-k'}^2-(\epsilon_k-\epsilon_{k'})^2}\hat c_{k'\...
During a calculation of the Renormalization constant of the ghosts in QCD I stumbled over the following question: When I calculate the self-energy of the Faddeev-Popov ghosts in $SU(N)$ non-abelian ...