More Feynman Diagrams


The basic vertex can be used to describe 8 situations which may occur with particle-boson interactions. Feynman diagrams do not deal with the energetics of an interaction, only the mechanics.

Taking as an example electron, positron & photon interactions:

photon emission from an energetic/excited electron

These vertices describe the absorption and emission of a photon from an electron.

photon absorption by an electron
photon emission from an energetic/excited positron

These vertices are equivalent to the first two, except they now involve anti-particles.

photon absorption by an electron
electon-positron generation from a photon

These vertices demonstrate the generation & annihilation of an electron-positron pair from an energetic photon.

electron-positron annihilation into a photon
electon-positron & photon generation from vacuum

These vertices demonstrate the generation & annihilation of an electron-positron pair and a photon from a vacuum.
 
These are perhaps the most difficult vertices to visualise.

electron-positron & photon annihilation to vacuum

All vertices conserve charge, linear momentum and angular momentum, however all of these processes break energy conservation. The processes are virtual, which means they cannot occur in isolation. Interactions that are built up of two or more of these vertices can conserve energy overall. The Heisenberg Uncertainty Principle dictates the length of time over which a conservation of energy violation can occur:

A simple example of a multi-vertex process is electrons scattering off each other. This occurs because like charges repel, so the two electrons will move together and then diverge:


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