View source for Physics:X and Y bosons

{{Short description|Hypothetical elementary particles}}
{{Infobox Particle
| bgcolour =
| name = X<sup>±</sup> and Y<sup>±</sup> bosons
| image = 
| caption = 
| num_types = 12
| composition = [[Physics:Elementary particle|Elementary particle]]
| statistics = [[Physics:Bosonic|Bosonic]]
| group = [[Physics:Gauge boson|Gauge boson]]
| generation =
| interaction = 
| particle = 
| antiparticle = 
| status = Hypothetical
| theorized = 
| discovered = 
| symbol = 
| mass = ≈ 10<sup>15</sup> [[Physics:Electronvolt#As a unit of energy|GeV]]/[[Physics:Speed of light|''c'']]<sup>2</sup> 
| mean_lifetime = 
| decay_particle = X: two [[Physics:Quark|quark]]s, or one [[Physics:Antiquark|antiquark]] and one charged antilepton <br> Y: two [[Physics:Quark|quark]]s, or one [[Physics:Antiquark|antiquark]] and one charged antilepton, or one [[Physics:Antiquark|antiquark]] and one antineutrino
| electric_charge = X: ±{{sfrac|4|3}} [[Physics: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|6}}
| num_spin_states = 3
}}
In [[Physics:Particle physics|particle physics]], the  '''X and Y bosons''' (sometimes collectively called "'''X bosons'''"<ref name="cheng-li">
{{cite book
 |year=1983
 |title=Gauge Theory of Elementary Particle Physics
 |publisher=[[Organization:Oxford University Press|Oxford University Press]]
 |isbn=0-19-851961-3
}}</ref>{{rp|437}}) are hypothetical [[Physics:Elementary particle|elementary particle]]s analogous to the [[Physics:W and Z bosons|W and Z bosons]], but corresponding to a unified force predicted by the [[Physics:Georgi–Glashow model|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 [[Physics:Quark|quark]]s (constituents of protons and others) to [[Physics:Lepton|lepton]]s (such as positrons), allowing violation of the conservation of [[Physics:Baryon number|baryon number]] thus permitting [[Physics:Proton decay|proton decay]].

However, the [[Astronomy:Hyper-Kamiokande|Hyper-Kamiokande]] has put a lower bound on the proton's [[Physics:Half-life|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 [[Physics:Georgi–Glashow model|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 modes:<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 [[Physics:Chirality|chirality]], {{Subatomic particle|Up quark}} is an [[Physics:Up quark|up quark]], {{Subatomic particle|Down antiquark}} is a down antiquark, and {{Subatomic particle|Positron}} is a [[Physics:Positron|positron]].

A Y&nbsp;boson would have the following three decay modes:<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 [[Physics:Chirality|chirality]] and the second has right-handed [[Physics:Chirality|chirality]], which always produces one fermion with the same handedness that would be produced by the decay of a [[Physics:W boson|W boson]], and one fermion with contrary handedness ("wrong handed").

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

In these reactions, neither the [[Physics:Lepton number|lepton number]] ({{mvar|L}}) nor the [[Physics:Baryon number|baryon number]] ({{mvar|B}}) is separately conserved, but the combination {{nobr| {{mvar|B &minus; L}} }} is. Different branching ratios between the X&nbsp;boson and its antiparticle (as is the case with the K-meson) would explain [[Physics:Baryogenesis|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 {{nobr|&thinsp; ( {{Subatomic particle|Up quark}} + {{Subatomic particle|Up quark}} + {{Subatomic particle|Down quark}} ) + {{Subatomic particle|Electron}} {{math|&thinsp;{{=}}&thinsp;}} {{Subatomic particle|link=yes|Proton}} + {{Subatomic particle|Electron}} &thinsp;}} shows it to be a hydrogen atom.

=== Origin ===

The X{{sup|±}} and Y{{sup|±}}&nbsp;bosons are defined respectively as the six {{math|Q {{=}} ± {{sfrac|4|3}}}} and the six {{math|Q {{=}} ± {{sfrac|1|3}}}} components of the final two terms of the adjoint '''24''' representation of [[Physics: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-[[Physics:Color charge|color charge]]s (equivalent to having two different normal color charges), while the negatively-charged X and Y carry normal [[Physics:Color charge|color charge]]s, and the signs of the Y&nbsp;bosons' [[Physics:Weak isospin|weak isospin]]s are always opposite the signs of their [[Physics:Electric charge|electric charge]]s. In terms of their action on <math>\ \mathbb{C}^5\ ,</math> X&nbsp;bosons rotate between a color index and the [[Physics:Weak isospin|weak isospin]]-up index, while Y&nbsp;bosons rotate between a color index and the [[Physics:Weak isospin|weak isospin]]-down index.

==See also==
* ''B'' − ''L''
* [[Physics:Grand unification theory|Grand unification theory]]
* [[Physics:Leptoquark|Leptoquark]]
* [[Physics:Proton decay|Proton decay]]
* W' and Z' bosons

==References==
{{reflist}}

{{particles}}

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

{{Sourceattribution|X and Y bosons}}