# How to compute the vertices from interaction lagrangian?

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1. Jul 9, 2015

### Nakul Soni

Hello all,
If I am having the the effective lagrangian which is actually free + interaction lagrangian (obtained from the minimal substitution for pseudoscalar and vector mesons). then how to compute the vertices of the interaction ?
I have taken into consideration of all symmetry breaking terms. How to construct the effective meson vertices to evaluate various feynman diagram for any meson scattering.

thank you

2. Jul 9, 2015

### Orodruin

Staff Emeritus
This should be explained in any QFT textbook and is no different from deriving the Feynman rules for the Lagrangian before symmetry breaking. What textbook are you using?

3. Jul 9, 2015

### Nakul Soni

Hello
I am using Peskin, Ashok Das, Itzykson & zuber.
I understood that things.
But I am studying the scattering of mesons. In which I know the interaction lagrangian. Now from that how to calculate the lagrangian for different vertices.
For example I am studying A+B -> C+D. say by exchange of E mesons. I know total lagrangian which is Lo+Lint. So how to compute the lagrangian for AEC, BED vertices ?

4. Jul 9, 2015

### RGevo

Look for the piece proportional to the fields A E C, this will give you the vertex piece. Do the same for B E D, then you just have to add the E propagator from the 2 point function for E (from the kinetic piece and mass term for E if they exist)

5. Jul 9, 2015

### Nakul Soni

Hello
Thank you very much for the response
I will try this and will come back to you soon.
Thank you