Massless particle

In particle physics, a massless particle is an elementary particle whose invariant mass is zero. There are two known gauge boson massless particles: the photon (carrier of electromagnetism) and the gluon (carrier of the strong force). However, gluons are never observed as free particles, since they are confined within hadrons.[1][2] In addition, the Weyl fermion discovered in 2015 is also expected to be massless.[3][4] However, literal Weyl fermions have not been confirmed to exist and are not required to exist by theory. When a Weyl fermion arises in matter, it is a quasiparticle like the phonon and therefore is not fundamental.

Neutrinos were originally thought to be massless. However, because neutrinos change flavor as they travel, at least two of the types of neutrinos must have mass.[5] The discovery of this phenomenon, known as neutrino oscillation, led to Canadian scientist Arthur B. McDonald and Japanese scientist Takaaki Kajita sharing the 2015 Nobel prize in physics.[6] The graviton is hypothesized to be the carrier of gravity, but it is unconfirmed and not predicted or required by the Standard Model.

NameSymbolAntiparticleCharge (e)SpinInteraction mediatedExistence
PhotonγSelf01ElectromagnetismConfirmed
Gluon
g
Self01Strong interactionConfirmed
GravitonGSelf02GravitationUnconfirmed

See also

References
  1. Valencia, G. (1992). "Anomalous Gauge-Boson Couplings At Hadron Supercolliders". AIP Conference Proceedings. 272 (2): 1572–1577. arXiv:hep-ph/9209237. Bibcode:1992AIPC..272.1572V. doi:10.1063/1.43410. S2CID 18917295.
  2. Debrescu, B. A. (2005). "Massless Gauge Bosons Other Than The Photon". Physical Review Letters. 94 (15): 151802. arXiv:hep-ph/0411004. Bibcode:2005PhRvL..94o1802D. doi:10.1103/PhysRevLett.94.151802. PMID 15904133. S2CID 7123874.
  3. "After 85-year search, massless particle with promise for next-generation electronics found".
  4. "Discovery of a Weyl fermion semimetal and topological Fermi arcs".
  5. "Neutrinos Have Mass".
  6. Day, Charles (2015-10-07). "Takaaki Kajita and Arthur McDonald share 2015 Physics Nobel". Physics Today. doi:10.1063/PT.5.7208. ISSN 0031-9228.
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