View source for X and Y bosons

{{Short description|Hypothetical elementary particles}}
{{about|bosons of a hypothetical new interaction|mesons with the same names|XYZ particle}}
{{Infobox Particle
| bgcolour =
| name = X<sup>±</sup> and Y<sup>±</sup> bosons
| image = 
| caption = 
| num_types = 12
| composition = [[Elementary particle]]
| statistics = [[Bosonic]]
| group = [[Gauge boson]]
| generation =
| interaction = 
| particle = 
| antiparticle = 
| status = Hypothetical
| theorized = 
| discovered = 
| symbol = 
| mass = ≈ 10<sup>15</sup> [[Electronvolt#As a unit of energy|GeV]]/[[speed of light|''c'']]<sup>2</sup> 
| mean_lifetime = 
| decay_particle = X: two [[quark]]s, or one [[antiquark]] and one charged [[antilepton]] {{br}} Y: two [[quark]]s, or one [[antiquark]] and one charged [[antilepton]], or one [[antiquark]] and one [[antineutrino]]
| electric_charge = X: ±{{sfrac|4|3}} [[Elementary charge|''e'']] {{br}} Y: ±{{sfrac|1|3}} ''e''
| weak_isospin_3 = X: ±{{sfrac|1|2}} {{br}} Y: ∓{{sfrac|1|2}} 
| B-L = ±{{sfrac|2|3}}
| X_charge = 0
| color_charge = triplet or antitriplet
| spin = 1
| weak_hypercharge = ±{{sfrac|5|3}}
| num_spin_states = 3
}}
In [[particle physics]], the  '''X and Y bosons''' (sometimes collectively called "'''X bosons'''"<ref name="cheng-li">
{{cite book
 |author1=Ta-Pei Cheng |author2=Ling-Fong Li|author2-link=Ling-Fong Li
 |year=1983
 |title=Gauge Theory of Elementary Particle Physics
 |publisher=[[Oxford University Press]]
 |isbn=0-19-851961-3
}}</ref>{{rp|437}}) are hypothetical [[elementary particle]]s analogous to the [[W and Z bosons]], but corresponding to a unified force predicted by the [[Georgi–Glashow model]], a [[grand unified theory]] (GUT).

Since the X and Y boson mediate the grand unified force, they would have unusual high mass, which requires more energy to create than the reach of any current particle collider experiment. Significantly, the X and Y&nbsp;bosons couple [[quark]]s (constituents of protons and others) to [[lepton]]s (such as positrons), allowing violation of the conservation of [[baryon number]] thus permitting [[proton decay]].

However, the [[Hyper-Kamiokande]] has put a lower bound on the proton's [[half-life]] as around 10<sup>34</sup> years.<ref name="gut1">{{cite web |title=Proton Decay Searches: Hyper-Kamiokande |url=http://www.hyper-k.org/en/physics/phys-protondecay.html |website=www.hyper-k.org |access-date=22 September 2020}}</ref> Since some grand unified theories such as the [[Georgi–Glashow model]] predict a half-life ''less'' than this, then the existence of X and Y bosons, as formulated by this particular model, remain hypothetical. 

== Details ==

An X&nbsp;boson would have the following two [[decay mode]]s:<ref name="cheng-li"/>{{rp|442}}
: {{Subatomic particle|X Boson}}{{sup|+}} &thinsp; &rarr; &thinsp; {{Subatomic particle|Up quark}}{{sub|L}} &thinsp; + &thinsp; {{Subatomic particle|Up quark}}{{sub|R}}
: {{Subatomic particle|X Boson}}{{sup|+}} &thinsp; &rarr; &thinsp; {{Subatomic particle|Positron}}{{sub|L}} &thinsp; + &thinsp; {{Subatomic particle|Down antiquark}}{{sub|R}}
where the two decay products in each process have opposite [[Chirality (physics)|chirality]], {{Subatomic particle|Up quark}} is an [[up quark]], {{Subatomic particle|Down antiquark}} is a [[down antiquark]], and {{Subatomic particle|Positron}} is a [[positron]].

A Y&nbsp;boson would have the following three [[decay mode]]s:<ref name="cheng-li"/>{{rp|442}}
: {{Subatomic particle|Y Boson}}{{sup|+}} &thinsp; &rarr; &thinsp; {{Subatomic particle|Positron}}{{sub|L}} &thinsp; + &thinsp; {{Subatomic particle|Up antiquark}}{{sub|R}}
: {{Subatomic particle|Y Boson}}{{sup|+}} &thinsp; &rarr; &thinsp; {{Subatomic particle|Down quark}}{{sub|L}} &thinsp; + &thinsp; {{Subatomic particle|Up quark}}{{sub|R}}
: {{Subatomic particle|Y Boson}}{{sup|+}} &thinsp; &rarr; &thinsp; {{Subatomic particle|Down antiquark}}{{sub|L}} &thinsp; + &thinsp; {{math|{{Subatomic particle|Electron antineutrino}}}}{{sub|R}}
where {{Subatomic particle|Up antiquark}} is an [[up antiquark]] and  {{math|{{Subatomic particle|Electron antineutrino}}}} is an [[electron antineutrino]].

The first product of each decay has left-handed [[Chirality (physics)|chirality]] and the second has right-handed [[Chirality (physics)|chirality]], which always produces one fermion with the same handedness that would be produced by the decay of a [[W boson]], and one fermion with contrary handedness ("wrong handed").

Similar decay products exist for the other [[Generation (particle physics)|quark–lepton generations]].

In these reactions, neither the [[lepton number]] ({{mvar|L}}) nor the [[baryon number]] ({{mvar|B}}) is separately conserved, but the combination {{nowrap|[[B − L|''B'' &minus; ''L'']]}} is. Different [[branching ratio]]s between the X&nbsp;boson and its antiparticle (as is the case with the [[K-meson]]) would explain [[baryogenesis]]. For instance, if an {{Subatomic particle|X Boson}}{{sup|+}} / {{Subatomic particle|X Boson}}{{sup|−}} pair is created out of energy, and they follow the two branches described above:
: {{Subatomic particle|X Boson}}{{sup|+}} &rarr; {{Subatomic particle|Up quark}}{{sub|L}} + {{Subatomic particle|Up quark}}{{sub|R}}&nbsp;,
: {{Subatomic particle|X Boson}}{{sup|−}} &rarr; {{Subatomic particle|Down quark}}{{sub|L}} + {{Subatomic particle|Electron}}{{sub|R}}&nbsp;;
re-grouping the result {{nowrap|( {{Subatomic particle|Up quark}} + {{Subatomic particle|Up quark}} + {{Subatomic particle|Down quark}} ) + {{Subatomic particle|Electron}} {{=}} {{Subatomic particle|link=yes|Proton}} + {{Subatomic particle|Electron}}}} shows it to be a hydrogen atom.

=== Origin ===

The X{{sup|±}} and Y{{sup|±}}&nbsp;bosons are defined respectively as the six {{nowrap|''Q'' {{=}} ± {{sfrac|4|3}}}} and the six {{nowrap|''Q'' {{=}} ± {{sfrac|1|3}}}} components of the final two terms of the adjoint '''24''' representation of [[Georgi–Glashow model|SU(5)]] as it transforms under the standard model's group:
: <math>\mathbf{24}\rightarrow (8,1)_0\oplus (1,3)_0\oplus (1,1)_0\oplus (3,2)_{-\frac{5}{6}}\oplus (\bar{3},2)_{\frac{5}{6}}.</math>

The positively-charged X and Y carry anti-[[color charge]]s (equivalent to having two different normal color charges), while the negatively-charged X and Y carry normal [[color charge]]s, and the signs of the Y&nbsp;bosons' [[weak isospin]]s are always opposite the signs of their [[electric charge]]s. In terms of their action on <math>\mathbb{C}^5,</math> X&nbsp;bosons rotate between a color index and the [[weak isospin]]-up index, while Y&nbsp;bosons rotate between a color index and the [[weak isospin]]-down index.

== See also ==
* [[B − L|''B'' − ''L'']]
* [[Grand unification theory]]
* [[Leptoquark]]
* [[Proton decay]]
* [[W′ and Z′ bosons]]
* [[List of hypothetical particles]]

== References ==
{{reflist}}

{{particles}}

[[Category:Gauge bosons]]
[[Category:Hypothetical elementary particles]]
[[Category:Grand Unified Theory]]
[[Category:Force carriers]]
[[Category:Subatomic particles with spin 1]]