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. 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.
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. Others address specific phenomena, including hidden-sector bosons such as dark photons or light force carriers proposed to explain nuclear anomalies.
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. 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.
+ Hypothetical bosons and fermions Name Spin Notes axion A pseudoscalar particle introduced in Peccei–Quinn theory to solve the strong-CP problem.curvatonScalar force-carrier that is presumed to have physically caused oscillations during cosmic inflation. dilaton Predicted in some string theories. graviphoton Also known as "gravivector". It appears in Kaluza–Klein theory.graviton Massless boson associated to gravitation. Included in many beyond the Standard Model theories. dual graviton Has been hypothesized as dual of graviton under electric–magnetic duality in supergravity. graviscalar Also known as "radion". It appears in Kaluza–Klein theory.hyperphotonHypothetical photon-like particle related to CP violations in kaon decay. inflaton Unidentified scalar force-carrier that is presumed to have physically caused cosmic inflation. majoron Predicted to understand neutrino masses by the seesaw mechanism.sterile neutrinoRight-handed neutrinos are compatible with the Standard Model but have never been observed.dual photon Dual of the photon under electric–magnetic duality magnetic photon Hypothetical particle similar to the photon in the presence of magnetic monopoles.pressuronhypothetical scalar particle which couples to both gravity and matter theorized in 2013.symmetronMediates the fifth force of the hypothetical symmetron field. X and Y bosons These leptoquarks are predicted by Grand Unified Theories to be heavier equivalents of the W and Z. W′ and Z′ bosons 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 is 0) include:
+SquarksNameSymbolSuperpartner ofSymbol sup squark up quark sdown squark down quark scharm squark charm quark sstrange squark strange quark stop squarkSearch For Pair Production of Stop Quarks Mimicking Top Event Signatures top quark sbottom squark bottom quark
+SleptonsNameSymbolSuperpartner ofSymbol selectron electron selectron sneutrino electron neutrino smuon muon smuon sneutrino muon neutrino stau tau stau sneutrino tau neutrino
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.
The predicted bosinos (spin ) are +Bosinos (superpartners of bosons) Name superpartner of: NotesaxinoaxionForms a supermultiplet, together with the saxion and axion, in supersymmetric extensions of Peccei–Quinn theory.dilatinodilatonCombines with the axion to form a complex scalar field gluino gluon Majorana fermions that interact via the strong force as a color octet. 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. gaugino (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, W, W, and W fields, the photino, zino, and wino are superpositions of the bino, wino, wino, and wino. 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:
+NameDescriptionChameleonCouples to matter more weakly than gravity, with non-linear variable effective mass. postulated as a dark energy candidate.AcceleronParticle that relates neutrino masses to dark energy.Quintessence particleUltralight 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.Phantom particleScalar 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.K-essence particleQuantum of a scalar with noncanonical kinetic structure; attractor dynamics drive cosmic acceleration without fine-tuned potential, behaving as effective vacuum energy at late times.QuintaxionAxion-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.Ultralight axionAxion-like particle with mass near Hubble scale (~10⁻³³ eV); field remains frozen cosmologically so particle condensate behaves as nearly constant vacuum energy today.String axionOne 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.Proca dark-energy bosonMassive vector boson with self-interaction potential; homogeneous temporal component acquires vacuum energy density, and particle excitations correspond to vector-dark-energy quanta driving acceleration.Dark-energy vector bosonGeneral cosmic vector particle whose coherent background breaks Lorentz symmetry cosmologically; effective negative pressure arises from potential energy dominating kinetic contributions at late times.Graviton condensate excitationCollective bosonic mode of a macroscopic graviton condensate; emergent quasiparticles encode vacuum energy of spacetime and can phenomenologically mimic cosmological-constant–like dark-energy behavior.
Dark matter candidates
The following categories are not unique or distinct: For example, either a WIMP or a WISP is also a FIP. +MeaningAbbreviationExplanationCandidatesFeebly interacting particleFIPParticles that interacts very weakly with conventional matter Massive gravitonsGravitationally interacting massive particleGIMPMassive particles that only interact with matter gravitationallyLightest supersymmetric particleLSPPredictions by supersymmetrySneutrino, gravitino, neutralinoStrongly interacting massive particleSIMPParticle that interact strongly between themselves and weakly with ordinary matterStable massive particlesSMPLong-lived particle with appreciable mass Weakly interacting massive particleWIMPHeavy particles that only interact with matter weaklyneutralino, sterile neutrinoWeakly interacting slender particleWISPLight particles that only interact with matter weaklyaxion 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):
+NameDate of anomalyOriginator of the anomalyDetailsN-ray1903Prosper-René BlondlotAn unknown form of radiation.Oops-Leon1976FermilabAnomalous resonance at 6 GeVValentine's day monopole1982Blas Cabrera NavarroSingle magnetic monopole detected on February 14, 1982.Meshugatron1989Fleischmann–Pons experimentPredicted by Edward Teller in 1989 in an attempt to understand cold fusion claimsOh-My-God particle1991High Resolution Fly's Eye Cosmic Ray Detector320 EeV cosmic ray, most energetic ultra-high-energy cosmic ray detected as of 2026Leptoquark (B-anomaly)2012Large Hadron ColliderHypothetical 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.Z′(Lμ−Lτ)2001Brookhaven E821Neutral 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.750 GeV diphoton2015Large Hadron ColliderResonance at 750 GeV signature of a bosonic particleX17 particle2015ATOMKIHypothesized new vector boson to explain nuclear experiments with beryllium.Amaterasu particle2021Telescope Array Project240 EeV cosmic ray
Others Cosmon, hypothetical state containing the observable universe before the Big Bang. Diproton (2He), nuclei consisting of two protons and no neutrons.Nuclear Physics in a Nutshell, C. A. Bertulani, Princeton University Press, Princeton, NJ, 2007, Chapter 1, . Observed, but without sufficient evidence. Diquark, hypothetical state of two quarks grouped inside a baryon. 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. 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. Pomerons, used to explain the elastic scattering of hadrons and the location of Regge poles in Regge theory. A counterpart to odderons. 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.
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.