Calculating the fine structure constant in Feynman diagrams

This means that in QED, as you add more vertices, the fine structure constant gets smaller, while in QCD, it gets larger.In summary, Griffith's Introduction to Elementary Particles explains that in QED, the fine structure constant has less influence on the strength of the EM interaction as more vertices are added, due to its small value of 1/137. However, in QCD, with a larger constant of 1, the influence of the constant increases as more vertices are added. Moreover, the amplitude for a Feynman diagram is computed by multiplying the constants for each vertex, resulting in a smaller fine structure constant in QED and a larger one in QCD.
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Griffith's Introduction to Elementary Particles, if I understand it correctly, states that in QED, the fine structure constant contributes less and less to the strength of the EM interaction as we add more and more vertices since the constant is so small (1/137). However, in QCD, since the constant is greater 1, it contributes more and more.

However, if you add 137 vertices, wouldn't that result in a constant of 1? And as you add more and more, you'll get higher values of the fine structure constant. Or do you multiply them so it gets smaller in QED, but larger in QCD.
 
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Phys12 said:
Or do you multiply them

If you are computing the amplitude for a Feynman diagram with multiple vertices, the constants for each vertex are multiplied.
 
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1. How is the fine structure constant calculated in Feynman diagrams?

The fine structure constant, denoted by α, is calculated in Feynman diagrams by using the formula α = e2/4πε0ℏc, where e is the elementary charge, ε0 is the vacuum permittivity, ℏ is the reduced Planck's constant, and c is the speed of light. This formula relates the strength of the electromagnetic force to the fundamental constants of nature.

2. What is the significance of the fine structure constant in Feynman diagrams?

The fine structure constant is a dimensionless quantity that characterizes the strength of the electromagnetic interaction between charged particles. It plays a crucial role in quantum electrodynamics, the theory that describes the behavior of electrons and photons.

3. How do Feynman diagrams help in calculating the fine structure constant?

Feynman diagrams provide a pictorial representation of the interactions between particles in quantum field theory. By using these diagrams, physicists can calculate the probability amplitudes for various particle interactions, which in turn can be used to determine the values of fundamental constants such as the fine structure constant.

4. What are some applications of calculating the fine structure constant in Feynman diagrams?

Calculating the fine structure constant in Feynman diagrams has numerous applications in modern physics. It helps in understanding the behavior of electrons and photons in quantum electrodynamics, determining the strength of the electromagnetic force between particles, and predicting the properties of atoms and molecules.

5. Are there any experimental methods for measuring the fine structure constant?

Yes, there are several experimental methods for measuring the fine structure constant, including precision measurements of the electron's magnetic moment, measurements of the Lamb shift in atomic spectra, and measurements of the anomalous magnetic moment of the muon. These methods have been used to determine the value of α with high accuracy.

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