Editing Elementary particle (section)

== Beyond the Standard Model ==
Although experimental evidence overwhelmingly confirms the predictions derived from the [[Standard Model]], some of its parameters were added arbitrarily, not determined by a particular explanation, which remain mysterious, for instance the [[hierarchy problem]]. Theories [[beyond the Standard Model]] attempt to resolve these shortcomings.

=== Grand unification ===
{{Main|Grand Unified Theory}}

One extension of the Standard Model attempts to combine the [[electroweak interaction]] with the [[strong interaction]] into a single 'grand unified theory' (GUT). Such a force would be [[spontaneous symmetry breaking|spontaneously broken]] into the three forces by a [[Higgs mechanism|Higgs-like mechanism]]. This breakdown is theorized to occur at high energies, making it difficult to observe unification in a laboratory. The most dramatic prediction of grand unification is the existence of [[X and Y bosons]], which cause [[proton decay]]. The non-observation of proton decay at the [[Super-Kamiokande]] neutrino observatory rules out the simplest GUTs, however, including SU(5) and SO(10).

=== Supersymmetry ===
{{Main|Supersymmetry}}

Supersymmetry extends the Standard Model by adding another class of symmetries to the [[Lagrangian (field theory)|Lagrangian]]. These symmetries exchange [[fermion]]ic particles with [[boson]]ic ones. Such a symmetry predicts the existence of [[supersymmetric particle]]s, abbreviated as ''[[sparticle]]s'', which include the [[slepton]]s, [[squark]]s, [[neutralino]]s, and [[chargino]]s. Each particle in the Standard Model would have a superpartner whose [[Spin (physics)|spin]] differs by {{1/2}} from the ordinary particle. Due to the [[supersymmetry breaking|breaking of supersymmetry]], the sparticles are much heavier than their ordinary counterparts; they are so heavy that existing [[particle collider]]s would not be powerful enough to produce them. Some physicists believe that sparticles will be detected by the [[Large Hadron Collider]] at [[CERN]].

=== String theory ===
{{Main|String theory}}

String theory is a model of physics whereby all "particles" that make up [[matter]] are composed of strings (measuring at the Planck length) that exist in an 11-dimensional (according to [[M-theory]], the leading version) or 12-dimensional (according to [[F-theory]]<ref>{{cite journal |doi=10.1016/0550-3213(96)00172-1 |arxiv=hep-th/9602022 |bibcode=1996NuPhB.469..403V |title=Evidence for F-theory |year=1996 |last1=Vafa |first1=Cumrun |journal=Nuclear Physics B |volume=469 |issue=3 |pages=403–415|s2cid=6511691 }}</ref>) universe. These strings vibrate at different frequencies that determine mass, electric charge, color charge, and spin. A "string" can be open (a line) or closed in a loop (a one-dimensional sphere, that is, a circle). As a string moves through space it sweeps out something called a ''[[world line#World lines as a tool to describe events|world sheet]]''. String theory predicts 1- to 10-branes (a 1-[[Membrane (M-theory)|brane]] being a string and a 10-brane being a 10-dimensional object) that prevent tears in the "fabric" of space using the [[uncertainty principle]] (e.g., the electron orbiting a hydrogen atom has the probability, albeit small, that it could be anywhere else in the universe at any given moment).

String theory proposes that our universe is merely a 4-brane, inside which exist the three space dimensions and the one time dimension that we observe. The remaining 7&nbsp;theoretical dimensions either are very tiny and curled up (and too small to be macroscopically accessible) or simply do not/cannot exist in our universe (because they exist in a grander scheme called the "[[multiverse]]" outside our known universe).

Some predictions of the string theory include existence of extremely massive counterparts of ordinary particles due to vibrational excitations of the fundamental string and existence of a massless spin-2 particle behaving like the [[graviton]].

=== Technicolor ===
{{Main|Technicolor (physics)}}

Technicolor theories try to modify the Standard Model in a minimal way by introducing a new QCD-like interaction. This means one adds a new theory of so-called Techniquarks, interacting via so called Technigluons. The main idea is that the Higgs boson is not an elementary particle but a bound state of these objects.

=== Preon theory ===
{{Main|Preon}}

According to preon theory there are one or more orders of particles more fundamental than those (or most of those) found in the Standard Model. The most fundamental of these are normally called preons, which is derived from "pre-quarks". In essence, preon theory tries to do for the Standard Model what the Standard Model did for the [[particle zoo]] that came before it. Most models assume that almost everything in the Standard Model can be explained in terms of three to six more fundamental particles and the rules that govern their interactions. Interest in preons has waned since the simplest models were experimentally ruled out in the 1980s.

=== Acceleron theory ===
[[Acceleron]]s are the hypothetical [[subatomic particle]]s that integrally link the newfound mass of the [[neutrino]] to the [[dark energy]] conjectured to be accelerating the [[metric expansion of space|expansion of the universe]].<ref name=acceleron />

In this theory, neutrinos are influenced by a new force resulting from their interactions with accelerons, leading to dark energy. Dark energy results as the universe tries to pull neutrinos apart.<ref name=acceleron>
{{cite web
 |date=28 Jul 2004
 |url=https://www.sciencedaily.com/releases/2004/07/040728090338.htm
 |title=New theory links neutrino's slight mass to accelerating Universe expansion
 |website=[[ScienceDaily]]
 |access-date=2008-06-05 |df=dmy-all
}}</ref> Accelerons are thought to interact with matter more infrequently than they do with neutrinos.<ref>
{{cite news
 |url=https://astronomy.com/news/2004/07/acceleron-anyone
 |title=Acceleron, anyone?
 |first=Francis |last=Reddy
 |date=2004-07-27
 |magazine=Astronomy
 |access-date=2020-04-20 |df=dmy-all
}}</ref>