X and Y bosons

Hypothetical elementary particles

This article is about bosons of a hypothetical new interaction. For mesons with the same names, see XYZ particle.

X± and Y± bosonsComposition| Elementary particle

|

Statistics| Bosonic
Family| Gauge boson
Status| Hypothetical
Types| 12
Mass| ≈ 1015 GeV/c2
Decays into| X: two quarks, or one antiquark and one charged antilepton
Y: two quarks, or one antiquark and one charged antilepton, or one antiquark and one antineutrino
Electric charge| X: ±⁠4/3⁠ e
Y: ±⁠1/3⁠ e
Color charge| triplet or antitriplet
Spin| 1
Spin states| 3
Weak isospin projection| X: ±⁠1/2⁠
Y: ∓⁠1/2⁠
Weak hypercharge| ±⁠5/3⁠
B − L| ±⁠2/3⁠
X| 0

In particle physics, the X and Y bosons (sometimes collectively called "X bosons"[1]: 437 ) are hypothetical elementary particles 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 bosons couple quarks (constituents of protons and others) to leptons (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 1034 years.[2] 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

[edit]

An X boson would have the following two decay modes:[1]: 442

+ ->

L \+

+ ->

L \+

where the two decay products in each process have opposite chirality,

is an up quark,

is a down antiquark, and

is a positron.

A Y boson would have the following three decay modes:[1]: 442

+ ->

L \+

+ ->

L \+

+ ->

L \+

where

is an up antiquark and

e is an electron antineutrino.

The first product of each decay has left-handed chirality and the second has right-handed 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 quark-lepton generations.

In these reactions, neither the lepton number (L) nor the baryon number (B) is separately conserved, but the combination  B − L is. Different branching ratios between the X boson and its antiparticle (as is the case with the K-meson) would explain baryogenesis. For instance, if an

+ /

− pair is created out of energy, and they follow the two branches described above:

+ ->

L \+

R ,

− ->

L \+

R ;

re-grouping the result  (

) +

shows it to be a hydrogen atom.

### Origin

[edit]

The X± and Y± bosons are defined respectively as the six Q = ± ⁠4/3⁠ and the six Q = ± ⁠1/3⁠ components of the final two terms of the adjoint 24 representation of SU(5) as it transforms under the standard model's group:

24 -> ( 8 , 1 ) 0 ⊕ ( 1 , 3 ) 0 ⊕ ( 1 , 1 ) 0 ⊕ ( 3 , 2 ) − 5 6 ⊕ ( 3 ¯ , 2 ) 5 6 {\displaystyle \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}}} .

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

## See also

[edit]

* B − L
* Grand unification theory
* Leptoquark
* Proton decay
* W' and Z' bosons

## References

[edit]

1. ^ a b c Ta-Pei Cheng; Ling-Fong Li (1983). Gauge Theory of Elementary Particle Physics. Oxford University Press. ISBN 0-19-851961-3.
2. ^ "Proton Decay Searches: Hyper-Kamiokande". www.hyper-k.org. Retrieved 22 September 2020.

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