Composition Elementary particle Bosonic Gauge boson Hypothetical 12 ≈ 1015 GeV/c2 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 X: ±.mw-parser-output .sfrac{white-space:nowrap}.mw-parser-output .sfrac.tion,.mw-parser-output .sfrac .tion{display:inline-block;vertical-align:-0.5em;font-size:85%;text-align:center}.mw-parser-output .sfrac .num{display:block;line-height:1em;margin:0.0em 0.1em;border-bottom:1px solid}.mw-parser-output .sfrac .den{display:block;line-height:1em;margin:0.1em 0.1em}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}⁠4/3⁠ e Y: ±⁠1/3⁠ e triplet or antitriplet 1 3 X: ±⁠1/2⁠ Y: ∓⁠1/2⁠ ±⁠5/3⁠ ±⁠2/3⁠ 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

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
e
R

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 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:

${\displaystyle \mathbf {24} \rightarrow (8,1)_{0}\oplus (1,3)_{0}\oplus (1,1)_{0}\oplus (3,2)_{-{\frac {5}{6))}\oplus ({\bar {3)),2)_{\frac {5}{6))}$.

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