How to compute the vertices from interaction lagrangian?

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Discussion Overview

The discussion revolves around the computation of interaction vertices from an effective Lagrangian in the context of quantum field theory (QFT), specifically focusing on meson scattering processes. Participants explore how to derive the vertices necessary for evaluating Feynman diagrams based on a given interaction Lagrangian that includes symmetry breaking terms.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant inquires about the method to compute interaction vertices from an effective Lagrangian that includes both free and interaction terms, specifically for meson scattering.
  • Another participant suggests that the process should be covered in standard QFT textbooks and asks which textbook is being used.
  • A participant mentions using textbooks by Peskin, Ashok Das, and Itzykson & Zuber, indicating a familiarity with the theoretical background but seeking specific guidance on calculating vertices for meson interactions.
  • One response advises looking for the terms in the Lagrangian that are proportional to the relevant fields (e.g., A, E, C) to extract the vertex contributions, and mentions the need to include the propagator for the exchanged meson.
  • A later reply reiterates the same advice about identifying the relevant terms in the Lagrangian for the vertices and adding the propagator for the exchanged meson.

Areas of Agreement / Disagreement

Participants seem to agree on the general approach to deriving vertices from the Lagrangian, but there is no consensus on the specific steps or methods to be used, as the discussion remains exploratory.

Contextual Notes

There are limitations in the discussion regarding the specific details of the interaction Lagrangian and the assumptions made about the fields involved. The exact mathematical steps for deriving the vertices are not fully resolved.

Who May Find This Useful

This discussion may be useful for students and researchers interested in quantum field theory, particularly those studying meson interactions and scattering processes.

Nakul Soni
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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
 
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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?
 
Hello
Thank you for your response.
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 ?

Thank you in advance.
 
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)
 
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RGevo said:
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)
Hello
Thank you very much for the response
I will try this and will come back to you soon.
Thank you
 

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