Drawing a Feynman Diagram: Lagrangian Basics

daymio
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I need help :(
How can I draw a Feynman Diagram, starting with a Lagrangian?
 
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1st Step: Read through any good introductory Quantum Field Theory Book.
2nd Step: There is no second step
 
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depends on the fields participating in your lagrangian...and the feynman diagram rules
 

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