X and Y bosons

Template:Short description Template:About Template:Infobox Particle In particle physics, the X and Y bosons (sometimes collectively called "X bosons"Template:Rp) 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. 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:Template:Rp

Template:Subatomic particleTemplate:Sup   →   Template:Subatomic particleTemplate:Sub   +   Template:Subatomic particleTemplate:Sub

Template:Subatomic particleTemplate:Sup   →   Template:Subatomic particleTemplate:Sub   +   Template:Subatomic particleTemplate:Sub

where the two decay products in each process have opposite chirality, Template:Subatomic particle is an up quark, Template:Subatomic particle is a down antiquark, and Template:Subatomic particle is a positron.

A Y boson would have the following three decay modes:Template:Rp

Template:Subatomic particleTemplate:Sup   →   Template:Subatomic particleTemplate:Sub   +   Template:Subatomic particleTemplate:Sub

Template:Subatomic particleTemplate:Sup   →   Template:Subatomic particleTemplate:Sub   +   Template:Subatomic particleTemplate:Sub

Template:Subatomic particleTemplate:Sup   →   Template:Subatomic particleTemplate:Sub   +   Template:MathTemplate:Sub

where Template:Subatomic particle is an up antiquark and Template:Math 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 (Template:Mvar) nor the baryon number (Template:Mvar) is separately conserved, but the combination Template:Nowrap 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 Template:Subatomic particleTemplate:Sup / Template:Subatomic particleTemplate:Sup pair is created out of energy, and they follow the two branches described above:

Template:Subatomic particleTemplate:Sup → Template:Subatomic particleTemplate:Sub + Template:Subatomic particleTemplate:Sub ,

Template:Subatomic particleTemplate:Sup → Template:Subatomic particleTemplate:Sub + Template:Subatomic particleTemplate:Sub ;

re-grouping the result Template:Nowrap shows it to be a hydrogen atom.

Origin

The XTemplate:Sup and YTemplate:Sup bosons are defined respectively as the six Template:Nowrap and the six Template:Nowrap components of the final two terms of the adjoint 24 representation of SU(5) as it transforms under the standard model's group:

$\mathrm{𝟐}\mathrm{𝟒}\to (8,1{)}_0\oplus (1,3{)}_0\oplus (1,1{)}_0\oplus (3,2{)}_{-\frac{5}{6}}\oplus (\overline{3},2{)}_{\frac{5}{6}}.$

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 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 ${ℂ}^5,$ 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
• List of hypothetical particles