page_title: Force carrier
section_title: Forces from the particle viewpoint
hierarchical_section_title: Force carrier / Forces from the particle viewpoint
caption_attribution_description: English: Feynman diagram of scattering between two electrons.
context_page_description: In quantum field theory, force carriers or messenger particles or intermediate particles are particles that give rise to forces between other particles. These particles are bundles of energy of a particular kind of field. There is one kind of field for every type of elementary particle. For instance, there is an electromagnetic field whose quanta are photons. The concept is especially important in particle physics where the force carrier particles that mediate the electromagnetic, weak, and strong interactions are called gauge bosons.
context_section_description: When one particle scatters off another, altering its trajectory, there are two ways to think about the process.  In the field picture, we imagine that the field generated by one particle caused a force on the other.  Alternatively, we can imagine one particle emitting a virtual particle which is absorbed by the other.  The virtual particle transfers momentum from one particle to the other.  This particle viewpoint is especially helpful when there are a large number of complicated quantum corrections to the calculation since these corrections can be visualized as Feynman diagrams containing additional virtual particles.
  Another example involving virtual particles is beta decay where a virtual W boson is emitted by a nucleon and then decays to e± and (anti)neutrino.
  The description of forces in terms of virtual particles is limited by the applicability of the perturbation theory from which it is derived.  In certain situations, such as low-energy QCD and the description of bound states, perturbation theory breaks down.
caption: A Feynman diagram of scattering between two electrons by emission of a virtual photon.
exif: {}