X and Y bosons

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

X^±and Y^±bosons

Composition	Elementary particle
Statistics	Bosonic
Family	Gauge boson
Status	Hypothetical
Types	12
Mass	≈ 1015GeV/c2
Decays into	X: twoquarks,or oneantiquarkand one chargedantilepton Y: twoquarks,or oneantiquarkand one chargedantilepton,or oneantiquarkand oneantineutrino
Electric charge	X: ±⁠4/3⁠e Y: ±⁠1/3⁠e
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

Inparticle physics,theX and Y bosons(sometimes collectively called "X bosons") are hypotheticalelementary particlesanalogous to theW and Z bosons,but corresponding to a unified force predicted by theGeorgi–Glashow model,agrand 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 couplequarks(constituents of protons and others) toleptons(such as positrons), allowing violation of the conservation ofbaryon numberthus permittingproton decay.

However, theHyper-Kamiokandehas put a lower bound on the proton'shalf-lifeas around 10³⁴years.Since some grand unified theories such as theGeorgi–Glashow modelpredict a half-lifelessthan 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 twodecay modes:

X
⁺  →  
u
_L  +  
u
_R

X
⁺  →  
e⁺
_L  +  
d
_R

where the two decay products in each process have oppositechirality,
u
is anup quark,
d
is adown antiquark,and
e⁺
is apositron.

A Y boson would have the following threedecay modes:

Y
⁺  →  
e⁺
_L  +  
u
_R

Y
⁺  →  
d
_L  +  
u
_R

Y
⁺  →  
d
_L  +  
ν
_eR

where
u
is anup antiquarkand
ν
_eis anelectron antineutrino.

The first product of each decay has left-handedchiralityand the second has right-handedchirality,which always produces one fermion with the same handedness that would be produced by the decay of aW boson,and one fermion with contrary handedness ( "wrong handed" ).

Similar decay products exist for the otherquark-lepton generations.

In these reactions, neither thelepton number(L) nor thebaryon number(B) is separately conserved, but the combinationB − Lis. Differentbranching ratiosbetween the X boson and its antiparticle (as is the case with theK-meson) would explainbaryogenesis.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 sixQ = ±⁠4/3⁠and the sixQ = ±⁠1/3⁠components of the final two terms of the adjoint24representation ofSU(5)as it transforms under the standard model's group:

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

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 normalcolor charges,and the signs of the Y bosons'weak isospinsare always opposite the signs of theirelectric charges.In terms of their action on$\ \mathbb {C} ^{5}\,$X bosons rotate between a color index and theweak isospin-up index, while Y bosons rotate between a color index and theweak isospin-down index.

See also

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