List of hypothetical particles

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This is a list of hypothetical particles.

Hypothetical particles are proposed subatomic or composite entities arising in theoretical particle physics and cosmology that have not been experimentally confirmed. They are typically introduced to address limitations of the Standard Model, unify fundamental interactions, or explain unresolved observations such as dark matter, neutrino masses, baryon asymmetry, or cosmic inflation.[1][2] Many are mathematically well defined within quantum field theory or its extensions and serve as mediators or constituents in speculative but testable frameworks beyond the Standard Model.[3]

Prominent classes include gauge or symmetry-related particles such as the graviton or graviphoton in quantum gravity and extra-dimensional theories, and supersymmetric partners (e.g., neutralinos or charginos) predicted by supersymmetry.[4][5] Others address specific phenomena, including hidden-sector bosons such as dark photons or light force carriers proposed to explain nuclear anomalies.[6]

Hypothetical particles also encompass predicted bound states (e.g., glueballs), topological objects such as magnetic monopoles, and unconventional statistical entities such as anyons or tachyons.[7][8] Collectively, they form a central component of theoretical model building, guiding experimental searches for physics beyond currently known particles.

Elementary particles

Some theories predict the existence of additional elementary bosons and fermions that are not found in the Standard Model.

More information Name, Spin ...
Hypothetical bosons and fermions
Name Spin Notes
axion
0
A pseudoscalar particle introduced in Peccei–Quinn theory to solve the strong-CP problem.[9]
curvaton
0
Scalar force-carrier that is presumed to have physically caused oscillations during cosmic inflation.[10]
dilaton
0
Predicted in some string theories.[11]
graviphoton
1
Also known as "gravivector".[12] It appears in Kaluza–Klein theory.[13]
graviton
2
Massless boson associated to gravitation. Included in many beyond the Standard Model theories.[14]
dual graviton
2
Has been hypothesized as dual of graviton under electric–magnetic duality in supergravity.[15]
graviscalar
0
Also known as "radion". It appears in Kaluza–Klein theory.[16]
hyperphoton
0
Hypothetical photon-like particle related to CP violations in kaon decay.[17][18][19]
inflaton
0
Unidentified scalar force-carrier that is presumed to have physically caused cosmic inflation.[20][21][22]
majoron
0
Predicted to understand neutrino masses by the seesaw mechanism.[23]
sterile neutrino
1/2
Right-handed neutrinos are compatible with the Standard Model but have never been observed.[24]
dual photon
1
Dual of the photon under electric–magnetic duality[25][26][27][28][29]
magnetic photon
1
Hypothetical particle similar to the photon in the presence of magnetic monopoles.[30]
pressuron
0
hypothetical scalar particle which couples to both gravity and matter theorized in 2013.[31]
symmetron
0
Mediates the fifth force of the hypothetical symmetron field.[32]
X and Y bosons
1
These leptoquarks are predicted by Grand Unified Theories to be heavier equivalents of the W and Z.[33]
W′ and Z′ bosons
1
Predicted by several extension of the electroweak interaction.[34]
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Particles predicted by supersymmetric theories

Supersymmetry predicts the existence of superpartners to particles in the Standard Model, none of which have been confirmed experimentally.[35] The sfermions (spin is 0) include:

More information , ...
Squarks
Name Symbol Superpartner of Symbol
sup squark up quark
sdown squark down quark
scharm squark charm quark
sstrange squark strange quark
stop squark[36] top quark
sbottom squark bottom quark
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More information , ...
Sleptons
Name Symbol Superpartner of Symbol
selectron electron
selectron sneutrino electron neutrino
smuon muon
smuon sneutrino muon neutrino
stau tau
stau sneutrino tau neutrino
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Another hypothetical sfermion is the saxion, superpartner of the axion. It forms a supermultiplet, together with the axino and the axion, in supersymmetric extensions of Peccei–Quinn theory.[37]

The predicted bosinos (spin 12) are

More information Name, superpartner of: ...
Bosinos (superpartners of bosons)
Name superpartner of: Notes
axino axion Forms a supermultiplet, together with the saxion and axion, in supersymmetric extensions of Peccei–Quinn theory.[38]
dilatino dilaton Combines with the axion to form a complex scalar field[39]
gluinogluonMajorana fermions that interact via the strong force as a color octet.
gravitinogravitonPredicted by supergravity (SUGRA).[40]
higgsinoHiggs bosonFor supersymmetry there is a need for several Higgs bosons, neutral and charged, according with their superpartners.[41][42]
photinophotonMixing with zino and neutral Higgsinos for neutralinos.
gaugino (wino, zino)W and Z bosonsThe charged wino mixing with the charged Higgsino for charginos, for the zino see line above.
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Just as the photon, Z and W± bosons are superpositions of the B0, W0, W1, and W2 fields, the photino, zino, and wino± are superpositions of the bino0, wino0, wino1, and wino2. No matter if one uses the original gauginos or this superpositions as a basis, the only predicted physical particles are neutralinos and charginos as a superposition of them together with the Higgsinos.

Other superpartner categories include:

  • Charginos, superpositions of the superpartners of charged Standard Model bosons: charged Higgs boson and W boson. The Minimal Supersymmetric Standard Model (MSSM) predicts two pairs of charginos.
  • Neutralinos, superpositions of the superpartners of neutral Standard Model bosons: neutral Higgs boson, Z boson and photon. The lightest neutralino is a leading candidate for dark matter. The MSSM predicts four neutralinos.
  • Goldstinos are fermions produced by the spontaneous breaking of supersymmetry; they are the supersymmetric counterpart of Goldstone bosons.
  • Sgoldstino, superpartners of goldstinos.

Dark energy candidates

The following hypothetical particles have been proposed to explain dark energy:

More information Name, Description ...
Name Description
Chameleon Couples to matter more weakly than gravity, with non-linear variable effective mass.[43] postulated as a dark energy candidate.[44]
Acceleron Particle that relates neutrino masses to dark energy.[45][46][47]
Quintessence particle Ultralight scalar boson whose vacuum expectation value evolves cosmologically; its coherent zero-momentum state produces negative pressure and late-time acceleration consistent with slowly rolling dark-energy models.[48][49]
Phantom particle Scalar boson with wrong-sign kinetic term yielding equation-of-state below −1; quantum excitations represent phantom dark energy causing super-accelerated expansion and possible future Big-Rip cosmology.[50][51]
K-essence particle Quantum of a scalar with noncanonical kinetic structure; attractor dynamics drive cosmic acceleration without fine-tuned potential, behaving as effective vacuum energy at late times.[52][53]
Quintaxion Axion-like pseudoscalar with extremely shallow periodic potential; misalignment energy evolves slowly and mimics quintessence, linking dark energy to Peccei–Quinn-type symmetries or string compactifications.[54][55]
Ultralight axion Axion-like particle with mass near Hubble scale (~10⁻³³ eV); field remains frozen cosmologically so particle condensate behaves as nearly constant vacuum energy today.[56][57]
String axion One of many ultralight pseudoscalars predicted by string compactifications; lightest modes can remain overdamped until recent epochs, providing axion-like particle interpretation of dark-energy density.[58][59]
Proca dark-energy boson Massive vector boson with self-interaction potential; homogeneous temporal component acquires vacuum energy density, and particle excitations correspond to vector-dark-energy quanta driving acceleration.[60][61]
Dark-energy vector boson General cosmic vector particle whose coherent background breaks Lorentz symmetry cosmologically; effective negative pressure arises from potential energy dominating kinetic contributions at late times.[62][63]
Graviton condensate excitation Collective bosonic mode of a macroscopic graviton condensate; emergent quasiparticles encode vacuum energy of spacetime and can phenomenologically mimic cosmological-constant–like dark-energy behavior.[64][65]
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Dark matter candidates

The following categories are not unique or distinct: For example, either a WIMP or a WISP is also a FIP.

More information Meaning, Abbreviation ...
Meaning Abbreviation Explanation Candidates
Feebly interacting particle FIP Particles that interacts very weakly with conventional matter Massive gravitons
Gravitationally interacting massive particle GIMP Massive particles that only interact with matter gravitationally
Lightest supersymmetric particle LSP Predictions by supersymmetry Sneutrino, gravitino, neutralino
Strongly interacting massive particle SIMP Particle that interact strongly between themselves and weakly with ordinary matter
Stable massive particles SMP Long-lived particle with appreciable mass
Weakly interacting massive particle WIMP Heavy particles that only interact with matter weakly neutralino, sterile neutrino
Weakly interacting slender particle WISP Light particles that only interact with matter weakly axion
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Hidden sector theories have also proposed forces that only interact with dark matter, like dark photons.

From experimental anomalies

These hypothetical particles were claimed to be found or hypothesized to explain unusual experimental results. They relate to experimental anomalies but have not been reproduced independently or might be due to experimental errors (in chronological order):

Feynman diagram of a possible 750 GeV diphoton excess
Fig. 6,7 from Prosper-René Blondlot: "Registration by Photography of the Action Produced by N Rays on a Small Electric Spark". Nancy, 1904.
More information Name, Date of anomaly ...
Name Date of anomaly Originator of the anomaly Details
N-ray 1903 Prosper-René Blondlot An unknown form of radiation.
Oops-Leon 1976 Fermilab Anomalous resonance at 6 GeV
Valentine's day monopole 1982 Blas Cabrera Navarro Single magnetic monopole detected on February 14, 1982.[66]
Meshugatron 1989 Fleischmann–Pons experiment Predicted by Edward Teller in 1989 in an attempt to understand cold fusion claims[67]
Oh-My-God particle 1991 High Resolution Fly's Eye Cosmic Ray Detector 320 EeV cosmic ray, most energetic ultra-high-energy cosmic ray detected as of 2026
Leptoquark (B-anomaly) 2012 Large Hadron Collider Hypothetical boson coupling quarks to leptons proposed to explain persistent flavor-universality violations in B-meson decays, notably RK and RD ratios, indicating potential new semileptonic interactions beyond Standard Model predictions.[68][69]
Z′(Lμ−Lτ) 2001 Brookhaven E821 Neutral gauge boson coupling to muon–tau lepton number difference proposed to explain muon anomalous magnetic-moment discrepancy and flavor anomalies while avoiding strong electron and quark coupling constraints.[70][71]
750 GeV diphoton 2015 Large Hadron Collider Resonance at 750 GeV signature of a bosonic particle
X17 particle 2015 ATOMKI Hypothesized new vector boson to explain nuclear experiments with beryllium.
Amaterasu particle 2021 Telescope Array Project 240 EeV cosmic ray
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Others

  • Cosmon, hypothetical state containing the observable universe before the Big Bang.[72]
  • Diproton (2He), nuclei consisting of two protons and no neutrons.[73] Observed, but without sufficient evidence.[74][75]
  • Diquark, hypothetical state of two quarks grouped inside a baryon.[76]
  • Fermi ball, hypothetical compound created in the early universe
  • Geons, electromagnetic or gravitational waves which are held together in a confined region by the gravitational attraction of their own field of energy.[77]
  • Kaluza–Klein towers of particles, predicted by some models of extra dimensions. The extra-dimensional momentum is manifested as extra mass in four-dimensional spacetime.[78]
  • Pomerons, used to explain the elastic scattering of hadrons and the location of Regge poles in Regge theory.[79] A counterpart to odderons.[80]
  • True muonium, atom composed of a muon and an anti-muon. Yet unobserved.
  • Familons, hypothetical Goldstone bosons arising from the spontaneous breaking of a global family symmetry that distinguishes between generations of quarks and leptons.[81]

By type

See also

References

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