How to compute the number of loops in a Feynman diagram?

1. Jun 22, 2005

lonelyphysicist

In doing my $$\phi^{3}$$ theory I didn't know exactly how to count the number of loops in a diagram given the number of vertices, internal and external lines. Is there a general algorithm in doing this? What if we have more than one interaction vertex (e.g. the Standard Model)?

PS. What does it mean when it says my thread has been "moved"?

2. Jun 22, 2005

vanesch

Staff Emeritus
It means an administrator thought that it better belonged to another subforum. If you talk about the "physical mass" thread, I'd like to know why it was moved, because I don't think it is really a college-level question !

cheers,
Patrick.

3. Jun 22, 2005

dextercioby

It's nonphysical $\lambda \phi^{3}$.The vertex (the OPI Green function of 4 points in the first order of perturbation theory) is made up of 3 scalar bosons.Self interaction doesn't mean creating/annihilating particles (that means there's no emission,nor absorption of particles),but only pure scattering (identical particles scattering one off another).

Read Zee's [1] argument against this theory and others involving other powers in $\phi$.

Daniel.

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[1] A.Zee,"Quantum Field Theory in a Nutshell",PUP,2003.

4. Jun 22, 2005

lonelyphysicist

Do you mean my thread was moved because $\lambda \phi^{3}$ is not a physical theory?

5. Jun 22, 2005

dextercioby

No,no,you had put in the wrong forum.It's Quantum Physics related and it should have been posted here. General Physics is not for such specific problems.

Daniel.

6. Jun 23, 2005