# feynman rules Definition and Topics - 46 Discussions

In theoretical physics, a Feynman diagram is a pictorial representation of the mathematical expressions describing the behavior and interaction of subatomic particles. The scheme is named after American physicist Richard Feynman, who introduced the diagrams in 1948. The interaction of subatomic particles can be complex and difficult to understand; Feynman diagrams give a simple visualization of what would otherwise be an arcane and abstract formula. According to David Kaiser, "Since the middle of the 20th century, theoretical physicists have increasingly turned to this tool to help them undertake critical calculations. Feynman diagrams have revolutionized nearly every aspect of theoretical physics." While the diagrams are applied primarily to quantum field theory, they can also be used in other fields, such as solid-state theory. Frank Wilczek wrote that the calculations which won him the 2004 Nobel Prize in Physics "would have been literally unthinkable without Feynman diagrams, as would [Wilczek's] calculations that established a route to production and observation of the Higgs particle."Feynman used Ernst Stueckelberg's interpretation of the positron as if it were an electron moving backward in time. Thus, antiparticles are represented as moving backward along the time axis in Feynman diagrams.
The calculation of probability amplitudes in theoretical particle physics requires the use of rather large and complicated integrals over a large number of variables. Feynman diagrams can represent these integrals graphically.
A Feynman diagram is a graphical representation of a perturbative contribution to the transition amplitude or correlation function of a quantum mechanical or statistical field theory. Within the canonical formulation of quantum field theory, a Feynman diagram represents a term in the Wick's expansion of the perturbative S-matrix. Alternatively, the path integral formulation of quantum field theory represents the transition amplitude as a weighted sum of all possible histories of the system from the initial to the final state, in terms of either particles or fields. The transition amplitude is then given as the matrix element of the S-matrix between the initial and the final states of the quantum system.

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1. ### I Consfused about the workflow for calculating scattering amplitudes with Feynman diagrams

In the following I will try to deduce the scattering amplitude for a specific interaction. My question is at the bottom, the entire rest is my reasoning to explain how I came to the results I present. My working Let's assume I would like to calculate the second order scattering amplitude in ##...
2. ### A Trace of a product of Dirac Matrices in a Fermion loop

I'm working out the quark loop diagram and I've drawn it as follows: where the greek letters are the Lorentz and Dirac indices for the gluon and quark respectively and the other letters are color indices. For this diagram I've written...
3. ### Calculating Divergent Amplitude in Phi-4 Theory

For the diagram In scalar field theory, I have obtained an integral which looks like $$\int_{0}^{\Lambda} \frac{d^4 q}{(2\pi)^4} \frac{i}{q^2 - m^2 + i\varepsilon} \frac{i}{(p - q)^2 - m^2 + i\varepsilon}$$ I am required to calculate this and obtain the divergent amplitude...
4. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 1: Introduction

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5. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 2: Introduction to Classical Field Theory

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6. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 3: Quantization of Real Scalar Field - 1

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7. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 4: Quantization of Real Scalar Field - 2

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8. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 5: Quantization of Real Scalar Field - 3

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9. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 6: Quantization of Real Scalar Field - 4

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10. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 7: Quantization of Complex Scalar Field

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11. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 8: Interacting Field Theory - 1

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12. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 9: Interacting Field Theory -2

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13. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 10: Interacting Field Theory - 3

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14. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 11: Interacting Field Theory - 4

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15. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 12: Interacting Field Theory - V

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16. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 13: Interacting Field Theory - VI

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17. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 14: Interacting Field Theory - 7

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18. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 15: Quantization of Electromagnetic Field 1

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19. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 16: Quantization of Electromagnetic Field 2

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20. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 17: Fermion Quantization 1

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21. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 18: Fermion Quantization 2

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22. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 19: Fermion Quantization 3

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23. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 20: Fermion Quantization 4

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24. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 21: Fermion Quantization 5

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25. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 22: Fermion Quantization 6

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26. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 23: The S-Matrix Expansion in QED 1

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27. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 24: The S-Matrix Expansion in QED 2

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28. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 25: Feynman Rules in QED 1

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29. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 26: Feynman Rules in QED 2

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30. ### Quantum Field Theory by Dr. Prasanta Tripathy (NPTEL):- Lecture - 27: Compton Scattering 1

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