View source for List of particles

{{Short description|List of particles in matter including fermions and bosons}}
This is a list of known and hypothesized microscopic particles in [[particle physics]], [[condensed matter physics]] and [[cosmology]].

== Standard Model elementary particles ==
{{Main|Elementary particle}}
{{hatnote|See [[Standard Model]] for the current consensus theory of these particles.}}
Elementary particles are particles with no measurable internal structure; that is, it is unknown whether they are composed of other particles.<ref name="PFIp1-3">
{{cite book |author1=Braibant |first=Sylvie |url=https://books.google.com/books?id=e8YUUG2pGeIC&pg=PA1 |title=Particles and Fundamental Interactions: An Introduction to Particle Physics |author2=Giacomelli |first2=Giorgio |author3=Spurio |first3=Maurizio |publisher=[[Springer (publisher)|Springer]] |year=2012 |isbn=978-94-007-2463-1 |edition=1st |pages=1}}</ref> They are the fundamental objects of [[quantum field theory]]. Many families and sub-families of elementary particles exist. Elementary particles are classified according to their [[Spin (physics)|spin]]. [[Fermion]]s have half-integer spin while [[boson]]s have integer spin. All the elementary particles of the [[Standard Model]] have been experimentally observed, including the [[Higgs boson]] in 2012.<ref>{{Cite journal |last1=Khachatryan |first1=V. |display-authors=etal |collaboration=CMS Collaboration |year=2012 |title=Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC |journal=[[Physics Letters B]] |volume=716 |issue=2012 |pages=30–61 |arxiv=1207.7235 |bibcode= 2012PhLB..716...30C|doi=10.1016/j.physletb.2012.08.021 }}</ref><ref>{{Cite journal |last1=Abajyan |first1=T. |collaboration=ATLAS Collaboration |display-authors=etal |title=Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC |journal=[[Physics Letters B]] |volume=716 |issue=2012 |pages=1–29 |year=2012 |arxiv=1207.7214  |bibcode= 2012PhLB..716....1A|doi=10.1016/j.physletb.2012.08.020|s2cid=119169617 }}</ref> Many other hypothetical elementary particles, such as the [[graviton]], have been proposed, but not observed experimentally.
{{Elementary particles|SM=yes}}

=== Fermions ===
[[Fermion]]s are one of the two fundamental classes of particles, the other being [[boson]]s. Fermion particles are described by [[Fermi–Dirac statistics]] and have [[quantum numbers]] described by the [[Pauli exclusion principle]]. They include the [[quarks]] and [[leptons]], as well as any [[composite particles]] consisting of an odd number of these, such as all [[baryons]] and many atoms and nuclei.

Fermions have half-integer spin; for all known elementary fermions this is {{sfrac|1|2}}''ħ''. All known fermions except [[neutrinos]], are also [[Dirac fermion]]s; that is, each known fermion has its own distinct [[antiparticle]]. It is not known whether the [[neutrino]] is a [[Dirac fermion]] or a [[Majorana fermion]].<ref>{{cite arXiv |eprint=1012.4469|last1=Kayser|first1=Boris|title=Two Questions About Neutrinos|class=hep-ph|year=2010}}</ref> Fermions are the basic building blocks of all [[matter]]. They are classified according to whether they interact via the [[strong interaction]] or not. In the Standard Model, there are 12 types of elementary fermions: six [[quark]]s and six [[lepton]]s.

==== Quarks ====
[[Quark]]s are the fundamental constituents of [[hadron]]s and interact via the [[strong force]]. Quarks are the only known carriers of [[fractional charge]], but because they combine in groups of three quarks (baryons) or in pairs of one quark and one [[antiquark]] (mesons), only integer charge is observed in nature. Their respective [[antiparticle]]s are the [[antiquark]]s, which are identical except that they carry the opposite electric charge (for example the up quark carries charge +{{sfrac|2|3}}''e'', while the up antiquark carries charge −{{sfrac|2|3}}''e''), color charge, and baryon number. There are six [[flavor (particle physics)|flavors]] of quarks; the three positively charged quarks are called "up-type quarks" while the three negatively charged quarks are called "down-type quarks".

{|class="wikitable sortable" style="margin:1em auto; text-align:center"
|+Quarks
|-
! Generation !! Name !! Symbol !! Antiparticle !! Spin{{br}}{{bracket|[[reduced Planck constant|''ħ'']]}} !! Charge{{br}}{{bracket|[[elementary charge|''e'']]}} !! data-sort-type="number"|Mass<ref name="PDG Light Quarks">{{cite web |title=Light quarks (u, d, s)|url=https://pdglive.lbl.gov/Particle.action?node=Q123&init=0 |website=pdglive.lbl.gov |publisher=Particle Data Group |access-date=24 September 2024}}</ref><ref name="PDG Charm Quark">{{cite web |title=c quark|url=https://pdglive.lbl.gov/Particle.action?node=Q004&init=0 |website=pdglive.lbl.gov |publisher=Particle Data Group |access-date=24 September 2024}}</ref><ref name="PDG Bottom Quark">{{cite web |title=b quark|url=https://pdglive.lbl.gov/Particle.action?node=Q005&init=0 |website=pdglive.lbl.gov |publisher=Particle Data Group |access-date=24 September 2024}}</ref><ref name="PDG Top Quark">{{cite web |title=t quark|url=https://pdglive.lbl.gov/Particle.action?node=Q007&init=0 |website=pdglive.lbl.gov |publisher=Particle Data Group |access-date=24 September 2024}}</ref>{{br}}{{bracket|[[electronvolt|MeV]]/[[speed of light|''c'']]<sup>2</sup>}}
|-
|rowspan=2| 1
| [[Up quark|up]] || u || {{Subatomic particle|up antiquark}}
|data-sort-value="1"|{{sfrac|1|2}} || +{{sfrac|2|3}} || {{val|2.16|0.07}}
|-
| [[Down quark|down]] || d || {{Subatomic particle|down antiquark}}
|data-sort-value="2"|{{sfrac|1|2}} || −{{sfrac|1|3}} || {{val|4.70|0.07}}
|-
|rowspan=2| 2
| [[Charm quark|charm]] || c || {{Subatomic particle|charm antiquark}}
|data-sort-value="3"|{{sfrac|1|2}} || +{{sfrac|2|3}} || {{val|1,273.0|4.6}}
|-
| [[Strange quark|strange]] || s || {{Subatomic particle|strange antiquark}}
|data-sort-value="4"|{{sfrac|1|2}} || −{{sfrac|1|3}} || {{val|93.5|0.8}}
|-
|rowspan=2| 3
| [[Top quark|top]] || t || {{Subatomic particle|top antiquark}}
|data-sort-value="5"|{{sfrac|1|2}} || +{{sfrac|2|3}} || {{val|172570|290}}
|-
| [[Bottom quark|bottom]] || b || {{Subatomic particle|bottom antiquark}}
|data-sort-value="6"|{{sfrac|1|2}} || −{{sfrac|1|3}} || {{val|4,183|7}}
|}

==== Leptons ====
[[Lepton]]s do not interact via the [[strong interaction]]. Their respective [[antiparticle]]s are the [[antilepton]]s, which are identical, except that they carry the opposite electric charge and lepton number. The antiparticle of an [[electron]] is an antielectron, which is almost always called a "[[positron]]" for historical reasons. There are six leptons in total; the three charged leptons are called "electron-like leptons", while the neutral leptons are called "[[neutrino]]s". Neutrinos are known to [[neutrino oscillation|oscillate]], so that neutrinos of definite [[flavour (particle physics)|flavor]] do not have definite mass: instead, they exist in a superposition of mass [[eigenstate]]s. The hypothetical heavy right-handed neutrino, called a "[[sterile neutrino]]", has been omitted.

{|class="wikitable sortable" style="margin:1em auto; text-align:center"
|+Leptons
|-
! Generation !! Name !! Symbol !! Antiparticle !! Spin{{br}}{{bracket|[[reduced Planck constant|''ħ'']]}} !! Charge{{br}}{{bracket|[[elementary charge|''e'']]}} !! Mass<ref name="PDG2016">{{cite journal |title=Review of Particle Physics |author=Particle Data Group |journal=Chinese Physics C |volume=40 |issue=10|pages=100001 |year=2016 |doi=10.1088/1674-1137/40/10/100001 |bibcode=2016ChPhC..40j0001P |hdl=1983/c6dc3926-daee-4d0e-9149-5ff3a8120574 |s2cid=125766528 |url=https://cds.cern.ch/record/2241948|hdl-access=free }}</ref>{{br}}{{bracket|[[electronvolt|MeV]]/[[speed of light|''c'']]<sup>2</sup>}}
|-
|rowspan=2| 1
| [[electron]] || {{Subatomic particle|electron}} || {{Subatomic particle|positron}}
|data-sort-value="4"| {{sfrac| 1 |2}} || −1 || 0.511{{refn|group=note|
A precise value of the electron mass is {{physconst|mec2_MeV|unit={{val|u=MeV/c2}}.}}
}}
|-
| [[electron neutrino]] || {{math|{{Subatomic particle|electron neutrino}}}} || {{math|{{Subatomic particle|electron antineutrino}}}}
|data-sort-value="1"| {{sfrac| 1 |2}} || &nbsp;&thinsp;0 || {{nowrap| < 0.0000022}}
|-
|rowspan=2| 2
| [[muon]] || {{math|{{Subatomic particle|muon}}}} || {{math|{{Subatomic particle|antimuon}}}}
|data-sort-value="5"| {{sfrac| 1 |2}} || −1 || 105.7{{refn|group=note|
A precise value of the muon mass is {{physconst|mmuc2_MeV|unit={{val|u=MeV/c2}}.}}
}}
|-
| [[muon neutrino]] || {{math|{{Subatomic particle|muon neutrino}}}} || {{math|{{Subatomic particle|muon antineutrino}}}}
|data-sort-value="2"| {{sfrac| 1 |2}} || &nbsp;&thinsp;0 || {{nowrap| < 0.170}}
|-
|rowspan=2| 3
| [[Tau (particle)|tau]] || {{math|{{Subatomic particle|tau}}}} || {{math|{{Subatomic particle|antitau}}}}
|data-sort-value="3"| {{sfrac| 1 |2}} || −1 || {{val|1,776.86|0.12}}
|-
| [[tau neutrino]] || {{math|{{Subatomic particle|tau neutrino}}}} || {{math|{{Subatomic particle|tau antineutrino}}}}
|data-sort-value="6"| {{sfrac| 1 |2}} || &nbsp;&thinsp;0 || {{nowrap| < 15.5}}
|}
{{reflist|group=note}}

=== Bosons ===
[[Boson]]s are one of the two fundamental particles having integral spinclasses of particles, the other being [[fermion]]s. Bosons are characterized by [[Bose–Einstein statistics]] and all have integer spins. Bosons may be either elementary, like [[photons]] and [[gluons]], or composite, like [[mesons]].

According to the [[Standard Model]], the elementary bosons are:

{| class="wikitable sortable" style="margin:1em auto; align: center; text-align: center;"
! Name !! Symbol !! Antiparticle !! Spin{{br}}{{bracket|[[reduced Planck constant|''ħ'']]}} !! Charge{{br}}{{bracket|[[elementary charge|''e'']]}} !! Mass<ref name="PDG2016" />{{br}}{{bracket|[[electronvolt|GeV]]/[[speed of light|''c'']]<sup>2</sup>}} !! Interaction mediated !!Observed
|-
| [[photon]] || {{math|γ}} || self || 1 || 0 || 0 || [[electromagnetism]] || {{yes|yes}}
|-
| [[W and Z bosons|W boson]] || {{Subatomic particle|W Boson-}} || {{Subatomic particle|W Boson+}} || 1 || ±1 || {{val|80.385|0.015}} || [[weak interaction]] || {{yes|yes}}
|-
| [[W and Z bosons|Z boson]] || {{Subatomic particle|Z Boson}} || self || 1 || 0 || {{val|91.1875|0.0021}} || [[weak interaction]] || {{yes|yes}}
|-
| [[gluon]] || {{Subatomic particle|Gluon}} || self || 1 || 0 || 0 || [[strong interaction]] || {{yes|yes}}
|-
| [[Higgs boson]] || {{Subatomic particle|Higgs boson}} || self || 0 || 0 ||{{val|125.09|0.24}} || [[mass]] || {{yes|yes}}
|}

The [[Higgs boson]] is postulated by the [[electroweak theory]] primarily to explain the origin of [[Mass|particle masses]]. In a process known as the "[[Higgs mechanism]]", the Higgs boson and the other gauge bosons in the Standard Model acquire mass via [[spontaneous symmetry breaking]] of the SU(2) gauge symmetry. The [[Minimal Supersymmetric Standard Model]] (MSSM) predicts several Higgs bosons. On 4 July 2012, the discovery of a new particle with a mass between {{val|125|and|127|u=GeV/c2}} was announced; physicists suspected that it was the Higgs boson. Since then, the particle has been shown to behave, interact, and decay in many of the ways predicted for Higgs particles by the Standard Model, as well as having even parity and zero spin, two fundamental attributes of a Higgs boson. This also means it is the first elementary scalar particle discovered in nature.

Elementary bosons responsible for the four [[fundamental force]]s of nature are called [[Force carrier|force particles]] ([[gauge boson]]s). The [[strong interaction]] is mediated by the [[gluon]], the [[weak interaction]] is mediated by the W and Z bosons, [[electromagnetism]] by the photon, and [[gravity]] by the graviton, which is still hypothetical.

== Composite particles ==
<!--'Composite particle' and 'Composite particles' redirect here-->
Composite particles are [[bound state]]s of elementary particles.

=== Hadrons ===
[[Hadron]]s are defined as [[strong interaction|strongly interacting]] '''composite particles'''<!--boldface per WP:R#PLA-->. Hadrons are either:
* [[Composite fermion]]s (especially 3 quarks), in which case they are called [[baryon]]s.
* [[Composite boson]]s (especially 2 quarks), in which case they are called [[meson]]s.

[[Quark model]]s, first proposed in 1964 independently by [[Murray Gell-Mann]] and [[George Zweig]] (who called quarks "aces"), describe the known hadrons as composed of valence [[quark]]s and/or antiquarks, tightly bound by the [[strong interaction|color force]], which is mediated by [[gluon]]s. (The interaction between quarks and gluons is described by the theory of [[quantum chromodynamics]].) A "sea" of virtual quark–antiquark pairs is also present in each hadron.

==== Baryons ====
[[File:Baryon decuplet.svg|thumb|A combination of three u, d or s-quarks with a total spin of {{sfrac|3|2}} form the so-called "baryon decuplet".]]
[[File:Quark_structure_proton.svg|thumb|Proton quark structure: 2 up quarks and 1 down quark.]]
{{main|List of baryons}}

Ordinary [[baryon]]s (composite [[fermion]]s) contain three valence quarks or three valence antiquarks each.
* [[Nucleon]]s are the fermionic constituents of normal atomic nuclei:
** [[Proton]]s, composed of two up and one down quark (uud)
** [[Neutron]]s, composed of two down and one up quark (ddu)
* [[Hyperon]]s, such as the Λ, Σ, Ξ, and Ω particles, which contain one or more [[strange quark]]s, are short-lived and heavier than nucleons. Although not normally present in atomic nuclei, they can appear in short-lived [[hypernucleus|hypernuclei]].
* A number of [[charm quark|charmed]] and [[bottom quark|bottom]] baryons have also been observed.
* [[Pentaquark]]s consist of four valence quarks and one valence antiquark.
* Other [[exotic baryon]]s may also exist.

==== Mesons ====
[[File:Noneto mesônico de spin 0.png|thumb|Mesons of spin 0 form a nonet.]]
{{main|List of mesons}}

Ordinary [[meson]]s are made up of a [[valence quark]] and a valence [[antiquark]]. Because mesons have integer [[Spin (physics)|spin]] (0 or 1) and are not themselves elementary particles, they are classified as "composite" [[bosons]], although being made of [[elementary particles|elementary]] [[fermions]]. Examples of mesons include the [[pion]], [[kaon]], and the [[J/ψ]]. In [[quantum hadrodynamics]], mesons mediate the [[residual strong force]] between nucleons.

At one time or another, positive [[signature]]s have been reported for all of the following [[exotic meson]]s but their existences have yet to be confirmed.
* A [[tetraquark]] consists of two valence quarks and two valence antiquarks;
* A [[glueball]] is a bound state of gluons with no valence quarks;
* [[Hybrid (particle physics)|Hybrid]] mesons consist of one or more valence quark–antiquark pairs and one or more real gluons.

=== Atomic nuclei ===
[[File:Helium atom QM.svg|thumb|A [[Uncertainty principle|semi-accurate]] depiction of the [[helium]] atom. In the nucleus, the protons are in red and neutrons are in purple. In reality, the nucleus is also spherically symmetrical.]]
{{hatnote|See [[Table of nuclides]] for a complete list of isotopes and isotones.}}

[[Atomic nucleus|Atomic nuclei]] typically consist of protons and neutrons, although exotic nuclei may consist of other baryons, such as [[hypertriton]] which contains a [[hyperon]]. These baryons (protons, neutrons, hyperons, etc.) which comprise the nucleus are called nucleons. Each type of nucleus is called a "[[nuclide]]", and each nuclide is defined by the specific number of each type of nucleon.
* "[[Isotope]]s" are nuclides which have the same number of protons but differing numbers of neutrons.
* Conversely, "[[isotone]]s" are nuclides which have the same number of neutrons but differing numbers of protons.
* "[[Isobar (nuclide)|Isobar]]s" are nuclides which have the same total number of nucleons but which differ in the number of each type of nucleon. [[Nuclear reaction]]s can change one nuclide into another.

=== Atoms ===
{{hatnote|See [[Periodic table]] for an overview of atoms.}}
[[Atom]]s are the smallest neutral particles into which matter can be divided by [[chemical reaction]]s. An atom consists of a small, heavy nucleus surrounded by a relatively large, light cloud of electrons. An atomic nucleus consists of 1 or more protons and 0 or more neutrons. Protons and neutrons are, in turn, made of quarks. Each type of atom corresponds to a specific [[chemical element]]. To date, 118 elements have been discovered or created.

[[Exotic atom]]s may be composed of particles in addition to or in place of protons, neutrons, and electrons, such as hyperons or muons. Examples include [[pionium]] ({{SubatomicParticle|Pion-}}{{nbsp}}{{SubatomicParticle|Pion+}}) and [[quarkonium]] atoms.

==== Leptonic atoms ====
Leptonic atoms, named using -[[onium]], are exotic atoms constituted by the bound state of a lepton and an antilepton. Examples of such atoms include [[positronium]] ({{SubatomicParticle|Electron}}{{nbsp}}{{SubatomicParticle|Positron}}), [[muonium]] ({{SubatomicParticle|Electron}}{{nbsp}}{{SubatomicParticle|Muon+}}), and "[[true muonium]]" ({{SubatomicParticle|Muon-}}{{nbsp}}{{SubatomicParticle|Muon+}}). Of these positronium and muonium have been experimentally observed, while "true muonium" remains only theoretical.

=== Molecules ===
{{hatnote|See [[List of compounds]] for a list of molecules.}}<!-- This section is linked from [[Molecule]] -->
[[Molecule]]s are the smallest particles into which a substance can be divided while maintaining the chemical properties of the substance. Each type of molecule corresponds to a specific [[chemical substance]]. A molecule is a composite of two or more atoms. Atoms are combined in a fixed proportion to form a molecule. Molecule is one of the most basic units of matter.

=== Ions ===
[[Ion]]s are charged atoms ([[monatomic ion]]s) or molecules ([[polyatomic ion]]s). They include cations which have a net positive charge, and anions which have a net negative charge.

===Other categories===
* [[Goldstone boson]]s are a massless excitation of a field that has been [[spontaneous symmetry breaking|spontaneously broken]]. The [[pion]]s are quasi-goldstone bosons (quasi- because they are not exactly massless) of the broken [[Chirality (physics)|chiral]] [[isospin]] symmetry of [[quantum chromodynamics]].
* [[Parton (particle physics)|Parton]], is a generic term coined by [[Richard P. Feynman|Feynman]] for the sub-particles making up a composite particle – at that time a baryon – hence, it originally referred to what are now called "[[quark]]s" and "[[gluon]]s".
* [[Odderon]], a particle composed of an odd number of gluons, detected in 2021.

== Quasiparticles ==
{{See also|List of quasiparticles}}
[[Quasiparticles]] are effective particles that exist in many particle systems. The field equations of [[condensed matter physics]] are remarkably similar to those of high energy particle physics. As a result, much of the theory of particle physics applies to condensed matter physics as well; in particular, there are a selection of field excitations, called [[quasi-particle]]s, that can be created and explored. These include:
* [[Anyon]]s are a generalization of fermions and bosons in two-dimensional systems like sheets of [[graphene]] that obeys [[braid statistics]].
* [[Exciton]]s are bound states of an [[electron]] and a [[electron hole|hole]].
* [[Magnon]]s are coherent excitations of electron spins in a material.
* [[Phonon]]s are vibrational modes in a [[crystal lattice]].
* [[Plasmon]]s are coherent excitations of a [[Plasma (physics)|plasma]].
* [[Polariton]]s are mixtures of [[photon]]s with other quasi-particles.
* [[Polaron]]s are moving, charged (quasi-) particles that are surrounded by ions in a material.

== Hypothetical particles ==
{{Main|List of hypothetical particles}}
=== Graviton ===
{| class="wikitable sortable" style="margin:1em auto; align: center; text-align: center;"
! Name !! Symbol !! Antiparticle !! Spin{{br}}{{bracket|[[reduced Planck constant|''ħ'']]}} !! Charge{{br}}{{bracket|[[elementary charge|''e'']]}} !! Mass<ref name="PDG2016" />{{br}}{{bracket|GeV/''c''<sup>2</sup>}} !! Interaction mediated !! Observed
|-
| [[graviton]] || G || self || 2 || 0 || 0 || [[gravitation]] || {{no|no}}
|}
The [[graviton]] is a hypothetical particle that has been included in some extensions to the Standard Model to mediate the [[gravitation]]al force. It is in a peculiar category between known and hypothetical particles: as an unobserved particle that is not predicted by, nor required for the [[Standard Model]], it belongs in the table of hypothetical particles. But gravitational force itself is a certainty, and expressing that known force in the framework of a [[quantum field theory]] requires a boson to mediate it.

If it exists, the graviton is expected to be [[Mass in special relativity|massless]] because the gravitational force has a very long range, and appears to propagate at the speed of light. The graviton must be a [[Spin (physics)|spin]]-2 [[boson]] because the source of gravitation is the [[stress–energy tensor]], a second-order [[tensor]] (compared with [[electromagnetism]]'s spin-1 [[photon]], the source of which is the [[four-current]], a first-order tensor). Additionally, it can be shown that any massless spin-2 field would give rise to a force indistinguishable from gravitation, because a massless spin-2 field would couple to the stress–energy tensor in the same way that gravitational interactions do. This result suggests that, if a massless spin-2 particle is discovered, it must be the graviton.<ref>For a comparison of the geometric derivation and the (non-geometric) spin-2 field derivation of general relativity, refer to box 18.1 (and also 17.2.5) of
{{cite book
 | last1=Misner | first1=C. W. | author-link=Charles W. Misner
 | last2=Thorne | first2=K. S. | author2-link=Kip Thorne
 | last3=Wheeler | first3=J. A. | author3-link=John A. Wheeler
 | date=1973
 | title=Gravitation
 | publisher=[[W. H. Freeman]]
 | isbn=0-7167-0344-0
}}</ref>

=== Dark matter candidates ===
{{See also|Dark matter#Composition}}
Many hypothetical particle candidates for [[dark matter]] have been proposed like [[Weakly interacting massive particle|weakly interacting massive particles]] (WIMP), [[WISP (particle physics)|weakly interacting slender particles]] (WISP), or [[Feebly interacting particle|feebly interacting particles]] (FIP).

=== Dark energy candidates ===
{{See also|Dark energy#Theories of dark energy}}
Hypothetical particle candidates to explain [[dark energy]] include the [[chameleon particle]] and the [[acceleron]].

== Auxiliary particles ==
[[Virtual particle]]s are mathematical tools used in calculations that exhibits some of the characteristics of an ordinary particle but do not obey the [[On shell and off shell|mass-shell relation]]. These particles are unphysical and unobservable. These include:
* [[Ghost (physics)|Ghost particles]], like [[Faddeev–Popov ghost|Faddeev–Popov ghosts]] and [[Pauli–Villars regularization|Pauli–Villars ghosts]]
* [[Spurion|Spurions]], auxiliary field in a quantum field theory that can be used to parameterize any [[Symmetry breaking|symmetry]] 
* [[Soft photon]]s, photons with energies below detectable in experiment.

There are also [[instanton]]s, field configurations which are a local minimum of the Yang–Mills field equation. Instantons are used in nonperturbative calculations of tunneling rates. Instantons have properties similar to particles, specific examples include:
* [[Caloron]]s, finite temperature generalization of instantons.
* [[Meron (physics)|Meron]]s, a field configuration which is a non-self-dual solution of the Yang–Mills field equation. The instanton is believed to be composed of two merons.
* [[Sphaleron]]s are a field configuration which is a saddle point of the [[Gauge theory|Yang–Mills field equations]]. Sphalerons are used in nonperturbative calculations of non-tunneling rates.
* [[Renormalon]]s, a possible type of singularity arising when using [[Borel summation]]. It is a counterpart of an instanton singularity.

== Classification by speed ==
* A [[bradyon]] (or tardyon) travels slower than the [[speed of light]] in vacuum and has a non-zero, [[Real number|real]] [[rest mass]].
* A [[Massless particle|luxon]] travels as fast as light in vacuum and has no rest mass.
* A [[tachyon]] is a hypothetical particle that travels [[Faster-than-light|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 [[Mass#Tachyonic particles and imaginary (complex) mass|imaginary rest mass]].

== See also ==
{{columns-list|colwidth=30em|
* [[Alternatives to the Standard Higgs Model]]
* [[Chronon]]
* [[Chirality (physics)|Chirality]] and [[Helicity (particle physics)|helicity]]
* [[List of fictional elements, materials, isotopes and subatomic particles]]
* [[Particle zoo]]
* [[Timeline of particle discoveries]]
}}

== References ==
{{reflist}}

{{Particles}}

[[Category:Physics-related lists|Particles]]
[[Category:Subatomic particles|∗]]
[[Category:Unsolved problems in physics]]
[[Category:Particles|*]]