# L3.4 Feynman Calculus: Higher-Order Diagrams | Summary and Q&A

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June 24, 2021
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L3.4 Feynman Calculus: Higher-Order Diagrams

## TL;DR

This content explains higher-order diagrams in particle physics, including the self-energy diagram, vertex correction diagrams, and box diagrams.

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### Q: What are higher-order diagrams in particle physics?

Higher-order diagrams are diagrams that go beyond the leading order or tree-level diagrams in understanding particle interactions. They involve corrections to particle masses, energies, and interaction vertices.

### Q: What is a self-energy diagram and how does it affect particle properties?

A self-energy diagram is a type of higher-order diagram where a particle's mass and energy are corrected. This diagram shows how the interaction with other particles affects the properties of the particle itself. There can be multiple self-energy diagrams depending on which particle is being corrected.

### Q: How do vertex correction diagrams differ from the primitive vertex?

Vertex correction diagrams involve corrections to the interaction vertex in particle interactions. Instead of the direct interaction shown in the primitive vertex, there are additional vertices involved in the diagram. This changes the strength and nature of the interaction between particles.

### Q: What are box diagrams and how do they change the interaction strength?

Box diagrams are higher-order diagrams where particles interact by going around in a box shape. These diagrams also modify the strength of the interaction. The resulting features of the interaction are different from the simple primitive vertex diagram.

## Summary & Key Takeaways

• The content introduces higher-order diagrams in particle physics, building on the concepts of Feynman diagrams, amplitudes, and phase space.

• Higher-order diagrams involve corrections to particle masses, energies, and interaction vertices.

• Three types of higher-order diagrams discussed are the self-energy diagram, vertex correction diagrams, and box diagrams.