Hypothetical particle that interacts only via gravity
Sterile neutrino, right-handed neutrino
Composition
Elementary particle
Statistics
Fermionic
Family
lepton
Generation
unknown
Interactions
gravity; other potential unknown interactions
Status
Hypothetical
Types
unknown
Mass
unknown
Electric charge
0
Color charge
none
Spin
1⁄2
Spin states
2
Weak isospin projection
0
Weak hypercharge
0
Chirality
right handed
B − L
depends on L charge assignment
X
−5
Sterile neutrinos (or inert neutrinos) are hypothetical particles (neutral leptons – neutrinos) that interact only via gravity and not via any of the other fundamental interactions of the Standard Model.[1] The term sterile neutrino is used to distinguish them from the known, ordinary active neutrinos in the Standard Model, which carry an isospin charge of ±+1/ 2 and engage in the weak interaction. The term typically refers to neutrinos with right-handed chirality (see right-handed neutrino), which may be inserted into the Standard Model. Particles that possess the quantum numbers of sterile neutrinos and masses great enough such that they do not interfere with the current theory of Big Bang nucleosynthesis are often called neutral heavy leptons (NHLs) or heavy neutral leptons (HNLs).[2]
The existence of right-handed neutrinos is theoretically well-motivated, because the known active neutrinos are left-handed and all other known fermions have been observed with both left and right chirality.[3] They could also explain in a natural way the small active neutrino masses inferred from neutrino oscillation.[3] The mass of the right-handed neutrinos themselves is unknown and could have any value between 1015 GeV and less than 1 eV.[4] To comply with theories of leptogenesis and dark matter, there must be at least 3 flavors of sterile neutrinos (if they exist).[5] This is in contrast to the number of active neutrino types required to ensure the electroweak interaction is free of anomalies, which must be exactly 3: the number of charged leptons and quark generations.
The search for sterile neutrinos is an active area of particle physics. If they exist and their mass is smaller than the energies of particles in the experiment, they can be produced in the laboratory, either by mixing between active and sterile neutrinos or in high energy particle collisions. If they are heavier, the only directly observable consequence of their existence would be the observed active neutrino masses. They may, however, be responsible for a number of unexplained phenomena in physical cosmology and astrophysics, including dark matter, baryogenesis or hypothetical dark radiation.[4] In May 2018, physicists of the MiniBooNE experiment reported a stronger neutrino oscillation signal than expected, a possible hint of sterile neutrinos.[6][7] However, results of the MicroBooNE experiment showed no evidence of sterile neutrinos in October 2021.[8]
^"Sterile neutrinos". All things neutrino. Retrieved 2021-04-29.
^Zyla, P.A.; et al. (Particle Data Group) (2020). "Review of Particle Physics" (PDF). Progress of Theoretical and Experimental Physics: Neutral Heavy Leptons, Searches for. 2020 (8): 083C01 [1168]. doi:10.1093/ptep/ptaa104.
^ abBoyarsky, A.; Drewes, M.; Lasserre, T.; Mertens, S.; Ruchayskiy, O. (January 2019). "Sterile neutrino Dark Matter". Progress in Particle and Nuclear Physics. 104: 1–45. arXiv:1807.07938. Bibcode:2019PrPNP.104....1B. doi:10.1016/j.ppnp.2018.07.004. S2CID 116613775.
^ abDrewes, Marco (2013). "The phenomenology of right handed neutrinos". International Journal of Modern Physics E. 22 (8): 1330019–1330593. arXiv:1303.6912. Bibcode:2013IJMPE..2230019D. doi:10.1142/S0218301313300191. S2CID 119161526.
^Ibe, Masahiro; Kusenko, Alexander; Yanagida, Tsutomu T. (2016-07-10). "Why three generations?". Physics Letters B. 758: 365–369. arXiv:1602.03003. Bibcode:2016PhLB..758..365I. doi:10.1016/j.physletb.2016.05.025. ISSN 0370-2693.
^Cite error: The named reference LS-20180601 was invoked but never defined (see the help page).
^Cite error: The named reference ARX-20180530 was invoked but never defined (see the help page).
^"MicroBooNE experiment's first results show no hint of a sterile neutrino". news.uchicago.edu (Press release). University of Chicago News. 27 October 2021.
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