Inparticle physics, theX and Y bosons (sometimes collectively called "X bosons"^[1]: 437) are hypotheticalelementary particles analogous 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 number thus permittingproton decay.

However, theHyper-Kamiokande has put a lower bound on the proton'shalf-life as around 10³⁴ years.^[2] Since some grand unified theories such as theGeorgi–Glashow model predict a half-lifeless than this, the existence of X and Y bosons, as formulated by this particular model, remains hypothetical.

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

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

A Y boson would have the following threedecay modes:^[1]: 442

whereu is anup antiquark andν
_e is anelectron antineutrino.

The first product of each decay has left-handedchirality and 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 −L is. Differentbranching ratios between the X boson and its antiparticle (as is the case with thekaon) would explainbaryogenesis. For instance, if anX⁺ /X⁻ pair is created out of energy, and they follow the two branches described above:

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

The X^± and Y^± bosons are defined respectively as the sixQ = ±⁠4/3⁠ and the sixQ = ±⁠1/3⁠ components of the final two terms of the adjoint24 representation ofSU(5) as it transforms under the standard model's group:$${\displaystyle \mathbf{24}\to (8,1{)}_0\oplus (1,3{)}_0\oplus (1,1{)}_0\oplus (3,2{)}_{-\frac{5}{6}}\oplus (\overline{3},2{)}_{\frac{5}{6}}.}$$

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 isospins are always opposite the signs of theirelectric charges. In terms of their action on${\displaystyle {\mathbb{C}}^5,}$ 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.

• B −L
• Grand Unified Theory
• Leptoquark
• Proton decay
• W′ and Z′ bosons
• List of hypothetical particles

• Gauge bosons
• Hypothetical elementary particles
• Grand Unified Theory
• Force carriers
• Subatomic particles with spin 1

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• Short description is different from Wikidata