Feynman diagram
Graphical method of representing the interactions of elementary particles. It was invented by Richard P. Feynman, who introduced the diagrams as an aid to calculating the processes that occur between electrons and photons. A Feynman diagram consists of two axes, one representing space, the other representing time. Electrons are represented as straight lines, while photons are shown as wavy lines. The interaction between particles appears as a junction of three lines, or a vertex. Feynman diagrams are now used to show all types of particle interactions.
Feynman diagram [′fīn·mən ‚dī·ə‚gram]
Feynman diagram
A pictorial representation of elementary particles and their interactions. Feynman diagrams show paths of particles in space and time as lines, and interactions between particles as points where the lines meet.
The illustration shows Feynman diagrams for electron-electron scattering. In each diagram, the straight lines represent space-time trajectories of noninteracting electrons, and the wavy lines represent photons, particles that transmit the electromagnetic interaction. External lines at the bottom of each diagram represent incoming particles (before the interactions), and lines at the top, outgoing particles (after the interactions). Interactions between photons and electrons occur at the vertices where photon lines meet electron lines. See Electron, Photon
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Each Feynman diagram corresponds to the probability amplitude for the process depicted in the diagram. The set of all distinct Feynman diagrams with the same incoming and outgoing lines corresponds to the perturbation expansion of a matrix element of the scattering matrix in field theory. This correspondence can be used to formulate the rules for writing the amplitude associated with a particular diagram. The perturbation expansion and the associated Feynman diagrams are useful to the extent that the strength of the interaction is small, so that the lowest-order terms, or diagrams with the fewest vertices, give the main contribution to the matrix element. See Perturbation (quantum mechanics), Scattering matrix
Since their introduction in quantum electrodynamics, Feynman diagrams have been widely applied in other field theories. They are employed in studies of electroweak interactions, certain situations in quantum chromodynamics, in acoustooptics, and in many-body theory in atomic, nuclear, plasma, and condensed matter physics. See Acoustooptics, Elementary particle, Fundamental interactions, Quantum chromodynamics, Quantum electrodynamics, Quantum field theory, Weak nuclear interactions
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