X and Y bosons

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 new type of force predicted by the Georgi–Glashow model, a grand unified theory. 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.

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

Details

The X and Y bosons couple quarks to leptons (such as a positron), allowing violation of the conservation of baryon number, and thus permitting proton decay.

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


X
+ →
u
 +
u

X
+ →
e+
 +
d

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 decay modes:[1]: 442 


Y
+ →
e+
 +
u

Y
+ →
d
 +
u

Y
+ →
d
 +
ν
e

where the first decay product in each process has left-handed chirality and the second has right-handed chirality and
ν
e is an electron antineutrino. Similar decay products exist for the other quark-lepton generations.

In these reactions, neither the lepton number (L) nor the baryon number (B) is conserved, but 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
 +
u
,
X
− →
d
 +
e−
; 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:

.

Thus, the positively-charged X and Y carry anti-color charges (equivalent to having two different 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. Ta-Pei Cheng; Ling-Fong Li (1983). Gauge Theory of Elementary Particle Physics. Oxford University Press. ISBN 0-19-851961-3.


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