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.

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

X^± and Y^± bosons

Composition	Elementary particle
Statistics	Bosonic
Status	Hypothetical
Types	12
Mass	≈ 10^15 GeV/c^2
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

Details

The X and Y bosons couple quarks to leptons, 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:

${\displaystyle \mathbf {24} \rightarrow (8,1)_{0}\oplus (1,3)_{0}\oplus (1,1)_{0}\oplus (3,2)_{-{\frac {5}{3}}}\oplus ({\bar {3}},2)_{\frac {5}{3}}}$.

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 ${\displaystyle \mathbb {C} ^{5}}$, 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

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

References

1. Ta-Pei Cheng; Ling-Fong Li (1983). Gauge Theory of Elementary Particle Physics. Oxford University Press. ISBN 0-19-851961-3.