X± and Y± bosons
CompositionElementary particle
StatisticsBosonic
FamilyGauge boson
StatusHypothetical
Types12
Mass≈ 1015 GeV/c2
Decays intoX: 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 chargeX: ±4/3 e
Y: ±1/3 e
Color chargetriplet or antitriplet
Spin1
Spin states3
Weak isospin projectionX: ±1/2
Y: ∓1/2
Weak hypercharge±5/6
B − L±2/3
X0

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

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


X
+   →  
u
L   +  
u
R

X
+   →  
e+
L   +  
d
R

where the two decay products in each process have opposite chirality,
u
 is an up quark,
d
 is a down antiquark, and
e+
 is a positron.

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


Y
+   →  
e+
L   +  
u
R

Y
+   →  
d
L   +  
u
R

Y
+   →  
d
L   +  
ν
eR

where
u
 is an up antiquark and
ν
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
X
+ /
X
− pair is created out of energy, and they follow the two branches described above:


X
+ →
u
L +
u
R ,

X
− →
d
L +
e−
R ;

re-grouping the result   (
u
 +
u
 +
d
 ) +
e−
  = 
p
 +
e−
   shows it to be a hydrogen atom.

Origin

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:

.

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 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

References

  1. 1 2 3 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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