diagrams illustrate the interactions between elementary particles
. Originaly used to solve problems involving electrons
, Feynman diagrams are now used to describe all kinds of particle interactions.
Each diagram has a time axis and a space axis. If the arrow on the particle's line points opposite the direction of forward time, it indicates an antiparticle
In the diagrams, a solid external line represents a real particle. A dashed, wavy or spiraled internal line indicates a virtual particle
or mediator particle.
A wavy line indicates a virtual photon, mediator of the electromagnetic force
. These interactions involve only leptons
A spiraled line is a virtual gluon
, mediator of the strong force
. These interactions involve only quarks
. (See: Quantum chromodynamics
A dashed line indicates a W+
or a W-
particle, mediators of the weak force
. These interactions can involve any type of particle