# List of hypothetical particles

This is a list of hypothetical subatomic particles in physics.

## Elementary particles

Some theories predict the existence of additional elementary bosons and fermions that are not found in the Standard Model.
Hypothetical bosons and fermions :
| Name | Spin | Notes |
| axion | 0 | A pseudoscalar particle introduced in Peccei–Quinn theory to solve the strong-CP problem. |
| dilaton | 0 | Predicted in some string theories. |
| graviphoton | 1 | Also known as "gravivector". It appears in Kaluza–Klein theory. |
| graviton | 2 | Massless boson associated to gravitation. Included in many beyond the Standard Model theories. |
| dual graviton | 2 | Has been hypothesized as dual of graviton under electric–magnetic duality in supergravity. |
| graviscalar | 0 | Also known as "radion". It appears in Kaluza–Klein theory. |
| hyperphoton | 0 | Hypothetical photon-like particle related to CP violations in kaon decay. |
| inflaton | 0 | Unidentified scalar force-carrier that is presumed to have physically caused cosmic inflation. |
| majoron | 0 | Predicted to understand neutrino masses by the seesaw mechanism. |
| sterile neutrino | ⁠ 1 /2⁠ | Right-handed neutrinos are compatible with the Standard Model but have never been observed. |
| dual photon | 1 | Dual of the photon under electric–magnetic duality |
| magnetic photon | 1 | Hypothetical particle similar to the photon in the presence of magnetic monopoles. |
| pressuron | 0 | hypothetical scalar particle which couples to both gravity and matter theorised in 2013. |
| symmetron | 0 | Mediates the fifth force of the hypothetical symmetron field. |
| X and Y bosons | 1 | These leptoquarks are predicted by Grand Unified Theories to be heavier equivalents of the W and Z. |
| W′ and Z′ bosons | 1 | Predicted by several extension of the electroweak interaction. |

### Particles predicted by supersymmetric theories

Supersymmetry predicts the existence of superpartners to particles in the Standard Model, none of which have been confirmed experimentally. The sfermions (spin-0) include:
squarks :
| Name | Symbol | Superpartner of | Symbol |
| sup squark | ${\tilde {u}}$ | up quark | $u$ |
| sdown squark | ${\tilde {d}}$ | down quark | $d$ |
| scharm squark | ${\tilde {c}}$ | charm quark | $c$ |
| sstrange squark | ${\tilde {s}}$ | strange quark | $s$ |
| stop squark | ${\tilde {t}}$ | top quark | $t$ |
| sbottom squark | ${\tilde {b}}$ | bottom quark | $b$ |
Sleptons :
| Name | Symbol | Superpartner of | Symbol |
| selectron | ${\tilde {e}}$ | electron | $e$ |
| selectron sneutrino | ${\tilde {\nu }}_{e}$ | electron neutrino | $\nu _{e}$ |
| smuon | ${\tilde {\mu }}$ | muon | $\mu$ |
| smuon sneutrino | ${\tilde {\nu }}_{\mu }$ | muon neutrino | $\nu _{\mu }$ |
| stau | ${\tilde {\tau }}$ | tau | $\tau$ |
| stau sneutrino | ${\tilde {\nu }}_{\tau }$ | tau neutrino | $\nu _{\tau }$ |
Another hypothetical sfermion is the saxion, superpartner of the axion. Forms a supermultiplet, together with the axino and the axion, in supersymmetric extensions of Peccei–Quinn theory.
The predicted bosinos (spin 1⁄2) are
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. |
| dilatino | dilaton | |
| gluino | gluon | Eight gluons and eight gluinos. |
| gravitino | graviton | Predicted by supergravity (SUGRA). |
| higgsino | Higgs boson | For supersymmetry there is a need for several Higgs bosons, neutral and charged, according with their superpartners. |
| photino | photon | Mixing with zino and neutral Higgsinos for neutralinos. |
| wino, zino | W and Z bosons | The charged wino mixing with the charged Higgsino for charginos, for the zino see line above. |
Just as the photon, Z and W$^±$ bosons are superpositions of the B$^0$, W$^0$, W$^1$, and W$^2$ fields, the photino, zino, and wino$^±$ are superpositions of the bino$^0$, wino$^0$, wino$^1$, and wino$^2$. 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:
| Name | Spin | Description |
| Chameleon | 0 | Couples to matter more weakly than gravity, with non-linear variable effective mass |
| Acceleron | 0 | Particle that relates neutrino masses to dark energy |

## Dark matter candidates

The following categories are not unique or distinct: For example, either a WIMP or a WISP is also a FIP.
| 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 gravitationaly | |
| 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 |
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:
| Name | Date of anomaly | Origin of the anomaly | Details |
| 750 GeV diphoton | 2015 | Large Hadron Collider. | Resonance at 750 GeV signature of a bosonic particle |
| Amaterasu particle | 2021 | Telescope Array Project | 240 EeV cosmic ray |
| Meshugatron | 1989 | Fleischmann–Pons experiment | Predicted by Edward Teller in 1989 in an attempt to understand cold fusion claims |
| N-ray | 1903 | Prosper-René Blondlot | An unknown form of radiation. |
| 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 2015 |
| Oops-Leon | 1976 | Fermilab | 6 GeV resonance |
| Valentine's day monopole | 1982 | Blas Cabrera Navarro | Single magnetic monopole detected on February 14, 1982. |
| X17 particle | 2015 | ATOMKI | Hypothesized new vector boson to explain nuclear experiments with beryllium. |

## Other

* Cosmon, hypothetical state containing the observable universe before the Big Bang.
* Diproton (He-2), nuclei consisting of two protons and no neutrons. Yet unobserved.
* Diquark, hypothetical state of two quarks grouped inside a baryon.
* Geons are electromagnetic or gravitational waves which are held together in a confined region by the gravitational attraction of their own field of energy.
* Kaluza–Klein towers of particles are predicted by some models of extra dimensions. The extra-dimensional momentum is manifested as extra mass in four-dimensional spacetime.
* Pomerons, used to explain the elastic scattering of hadrons and the location of Regge poles in Regge theory. A counterpart to odderons.

### By type

* Branons, scalar fields predicted in brane world models.
* Composite Higgs, models that consider the Higgs boson to be a composite particle.
** Higgs doublets are hypothesized by some theories of physics beyond the standard model.
* Continuous spin particle are hypothetical massless particles related to the classification of the representations of the Poincaré group.
* Cryptons, any particle from the dark sector of string theory landscape.
* Elementary particles that are not bosons or fermions:
** Paraparticles, exotic particles that can survive in a 3D-space and follow parastatistics
** Plektons, particles that follow Braid statistics
* Exotic particles, particles with exotic properties like negative mass or complex mass.
* Exotic hadrons, particles composed of unusual combinations of quarks and gluons.
** Exotic mesons
** Exotic baryons
** Glueball, hypothetical particle that consist of only gluons.
** Quark bound states beyond the pentaquark, like hexaquarks and heptaquarks.
* Leptoquark, hypothetical particles that are neither bosons or fermions but carry lepton and baryon numbers.
* Magnetic monopole is a generic name for particles with non-zero magnetic charge. They are predicted by Grand Unification Theories. These may include:
** Dirac monopoles, monopole that would allow charge quantization.
** 't Hooft–Polyakov monopoles, Dirac monopole but without Dirac strings.
** Wu–Yang monopoles, point-like monopole with potential of the form 1/r.
** Dyons, extensions of the idea of a magnetic monopole.
* Majorana fermions, fermions that are their own anti-particle
* Mesonic molecule, two mesons bound together by strong force.
* Micro black hole, sub-atomic sized black holes.
** Black hole electron, microscopic black hole with the properties of an electron.
* Minicharged particle are hypothetical subatomic particles charged with a tiny fraction of the electron charge.
* Mirror particles are predicted by theories that restore parity symmetry.
* Neutronium, hypothetical nuclei consisting only of neutrons (more than one). Examples include the tetraneutron.
* Preons were suggested as subparticles of quarks and leptons, but modern collider experiments have all but ruled out their existence.
** Rishons, particles from the Rishon model of preons.
* From superseded and obsolete theories
** Caloric rays used until the 19th century to explain thermal radiation.
** Light corpuscles, hypothetical classical particles used to explain optical phenomena.
** Phlogiston, hypothetical combustible content in matter used to explain thermodynamics before the 18th century.
** Ultramundane corpuscles, from Le Sage's theory of gravitation, used to explain gravitational phenomena.
* Strangelet, hypothetical particle that could form matter consisting of strange quarks.
* R-hadron, bound particle of a quark and a supersymmetric particle.
* T meson, hypothetical mesons composed of a top quark and one additional subatomic particle. Examples include the theta meson, formed by a top and an anti-top.
* Tachyons is a hypothetical particle that travels faster than the speed of light so they would paradoxically experience time in reverse (due to inversion of the theory of relativity) and would violate the known laws of causality. A tachyon has an imaginary rest mass.
* True muonium, atom composed of a muon and an anti-muon. Yet unobserved.
* Unparticles, hypothetical particles that are massless and scale invariant.
* Weyl fermions, hypothetical spin-1/2 massless particles, only found as a quasiparticle.