# Treating Mass as a perturbation

by Sekonda
Tags: mass, perturbation, treating
 P: 209 Hello again, I also have another question, somewhat related to my previous, on the topic of the Klein-Gordon equation but treating the mass as a perturbation. The feynman diagram shows the particular interaction: I believe the cross is the point of interaction via the perturbation (the mass), we model the perturbation: $$\delta V=m^2$$ and subsequently use this in the calculation for the transition amplitude, we use plane-wave solutions of the ingoing and outgoing states. Alike to my previous question, I'm not really sure what this means to model some potential as a mass? Can anyone explain why we do this and maybe exactly what is happening in this particular feynman diagram? I can try to embelish if needs be, please tell me if there are any inconsistencies or errors I have made in my explanation of my problem! Thanks, SK