Massless particle

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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 semimetal or Weyl fermion discovered in 2015 is also massless.[3][4]

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]

Name Symbol Antiparticle Charge (e) Spin Interaction mediated Existence
Photon γ Self 0 1 Electromagnetism Confirmed
Self 0 1 Strong interaction Confirmed
Weyl fermion Self 0 ½ N/A Unconfirmed*
Graviton G Self 0 2 Gravitation Unconfirmed
  • Note that although literal Weyl fermions have never been experimentally confirmed to physically exist, certain systems can act collectively such that they seem to contain Weyl fermion quasiparticles.

See also[edit]


  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.